DOC AIRBUS | AMM A320FT/TISS - TERRAIN AWARENESS AND WARNING SYSTEM - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
A. Presentation
The purpose of the T/TISS (Traffic and Terrain Integrated Surveillance System) -TAWS (Terrain Awareness and Warning System) is to alert the crew in a timely manner of a developing hazardous situation ahead of the aircraft which would result in a Controlled Flight Into Terrain (CFIT) accident if no specific crew action was performed.
The TAWS function therefore implements CFIT prevention concepts which aimed to ultimately prevent most of CFIT events.
This function delivers appropriate cautions and warnings, without nuisance alerts, whenever the aircraft is abnormally and hazardously approaching the surrounding terrain.
The T/TISS-TAWS achieves this objective by accepting a variety of aircraft parameters as inputs, applying alerting algorithms, and providing the flight crew with aural and visual alerts and displays if the boundaries of any alerting envelope are exceeded.
An overall system block diagram is shown in figure:
The T/TISS-TAWS system includes:
The purpose of the T/TISS (Traffic and Terrain Integrated Surveillance System) -TAWS (Terrain Awareness and Warning System) is to alert the crew in a timely manner of a developing hazardous situation ahead of the aircraft which would result in a Controlled Flight Into Terrain (CFIT) accident if no specific crew action was performed.
The TAWS function therefore implements CFIT prevention concepts which aimed to ultimately prevent most of CFIT events.
This function delivers appropriate cautions and warnings, without nuisance alerts, whenever the aircraft is abnormally and hazardously approaching the surrounding terrain.
The T/TISS-TAWS achieves this objective by accepting a variety of aircraft parameters as inputs, applying alerting algorithms, and providing the flight crew with aural and visual alerts and displays if the boundaries of any alerting envelope are exceeded.
An overall system block diagram is shown in figure:
The T/TISS-TAWS system includes:
- two TAWS databases (one with terrain and airport data and other with obstacle data)
- a performance database (aircraft climb capability) for alert computation and terrain display.
The system is made up of the T/TISS computer which is a single Line Replaceable Unit (LRU) located in the avionics compartment. The computer includes TAWS processors and an Input/Output (I/O) circuitry in a single circuit card assembly. The TAWS processors and the I/O circuitry are independent from the TCAS functions, except where common I/O pin-connectors and power supply are shared by both functions.
The system is linked to the following systems/components: - aircraft sensors and other systems that provide the input signals
- cockpit audio systems (loudspeakers or Audio Management Unit (AMU))
- alert and digital outputs to the Electronic Flight Instrument System (EFIS) displays (for alert and system status messages)
- EFIS Navigation Displays (ND) for display of terrain
- switching relays to switch display outputs from weather display to terrain display.
B. Embedded Functions
The following alerting functions modes are integrated in the T/TISS-TAWS:
The following alerting functions modes are integrated in the T/TISS-TAWS:
- Basic TAWS Modes:Reactive Modes 1 to 5, mainly based on Radio Altitude (RA)
- Predictive modes:
Collision Prediction and Alerting (CPA) function and Obstacle Collision Prediction and Alerting (OCPA) function which provides a forward-looking terrain alerting capabality.
Terrain Hazard Display (THD) function, Obstacle Hazard Display (OHD) function and Eleview, which provide a horizontal terrain/obstacle depiction based both on relative (THD/OHD mode) and absolute (Eleview mode) terrain/obstacle elevation.
(1) Basic TAWS Modes
- Excessive rate of descent with respect to terrain detection (reactive Mode 1 per DO-161a)
- Excessive closure rate to terrain detection (reactive Mode 2 per DO-161a)
- Excessive altitude loss after takeoff detection (reactive Mode 3 per DO-161a)
- Detection of an incorrect aircraft configuration with respect to terrain (reactive Mode 4, equivalent to previous TAWS installations)
- Excessive glide path deviation detection (reactive Mode 5 per DO-161a).
(2) Predictive TAWS Modes
- Collision Prediction and Alerting (Forward-Looking Terrain Avoidance (FLTA) and Premature Descent Alert (PDA) functions as defined in TSO-C151b)
- Obstacle Collision Prediction and Alerting
- Terrain/Obstacle Hazard Display and Eleview Display.
(a) Collision Prediction and Alerting (CPA)
The Collision Prediction and Alerting function provides alerts to inform the crew that the flight path they are following is hazardous due to the presence of terrain.
A pull-up evasive action is considered as the basic recovery maneuver ("Pull Up" warning). If this maneuver is not possible, a turn-around recovery is indicated ("Avoid Terrain" warning).
The TAWS, through the CPA, is intended to provide alerts in particular in the following CFIT situations:
The TAWS, through the CPA, generates a "Pull Up" warning or an "Avoid Terrain" warning depending on the aircraft situation with respect to the terrain, and whenever possible generates a terrain caution or a premature descent caution, in anticipation of the warnings.
The Ground Collision Avoidance Module (GCAM) ensures a very low rate of nuisance alerts to keep the crew confident in the generated alerts. It addresses some specific situations such as situations of normal aircraft operation according to procedures at altitudes significantly below the surrounding local terrain height (approaches in steep valleys).
The Collision Prediction and Alerting function provides alerts to inform the crew that the flight path they are following is hazardous due to the presence of terrain.
A pull-up evasive action is considered as the basic recovery maneuver ("Pull Up" warning). If this maneuver is not possible, a turn-around recovery is indicated ("Avoid Terrain" warning).
The TAWS, through the CPA, is intended to provide alerts in particular in the following CFIT situations:
- hazardous descent rate with respect to terrain
- hazardous closure rate with respect to terrain
- hazardous situation during a turning flight
- hazardous situation due to high terrain ahead that could not be cleared by a pull-up maneuver
- premature descent.
The TAWS, through the CPA, generates a "Pull Up" warning or an "Avoid Terrain" warning depending on the aircraft situation with respect to the terrain, and whenever possible generates a terrain caution or a premature descent caution, in anticipation of the warnings.
The Ground Collision Avoidance Module (GCAM) ensures a very low rate of nuisance alerts to keep the crew confident in the generated alerts. It addresses some specific situations such as situations of normal aircraft operation according to procedures at altitudes significantly below the surrounding local terrain height (approaches in steep valleys).
(b) Obstacle Collision Prediction and Alerting (OCPA)
The Obstacle Collision Prediction and Alerting function provides alerts to inform the crew that the flight path they are following is hazardous due to the presence of man-made obstacles.
The function is based on a dedicated and uploadable man-made obstacle database.
It brings the CPA function new capability of preventing CFIT, by taking in account the obstacles in the detection of hazardous situations.
This module is intended to provide alerts in particular in the following CFIT situations:
The Obstacle Collision Prediction and Alerting function provides alerts to inform the crew that the flight path they are following is hazardous due to the presence of man-made obstacles.
The function is based on a dedicated and uploadable man-made obstacle database.
It brings the CPA function new capability of preventing CFIT, by taking in account the obstacles in the detection of hazardous situations.
This module is intended to provide alerts in particular in the following CFIT situations:
- Hazardous descent rate with respect to obstacles
- Hazardous closure rate with respect to obstacles
- Hazardous situation during a turning flight with respect to obstacles.
(c) Terrain / Obstacle Hazard Display (THD / OHD) and Eleview
The Terrain / Obstacle Hazard Display function, combined with Eleview Display, outputs a display of terrain / obstacle data in weather radar format per ARINC-708/708A (ARINC 453) bus format. The terrain / obstacle data is displayed on the NDs.
When the terrain display is present, it replaces the weather radar display. The terrain display can be made available to the flight crew at any time. When the conditions for either a terrain caution or a terrain warning are detected, the T/TISS-TAWS automatically switches cockpit displays between the weather radar and the terrain display. Both pilots can manually select terrain or weather radar display using the TERR ON ND pushbutton switches at any time, even if an alert is in progress.
The Terrain / Obstacle Hazard Display function, combined with Eleview Display, outputs a display of terrain / obstacle data in weather radar format per ARINC-708/708A (ARINC 453) bus format. The terrain / obstacle data is displayed on the NDs.
When the terrain display is present, it replaces the weather radar display. The terrain display can be made available to the flight crew at any time. When the conditions for either a terrain caution or a terrain warning are detected, the T/TISS-TAWS automatically switches cockpit displays between the weather radar and the terrain display. Both pilots can manually select terrain or weather radar display using the TERR ON ND pushbutton switches at any time, even if an alert is in progress.
C. Runway Information Output capability
T/TISS-TAWS includes a runway detection algorithm which purpose is to select the approached runway and to output the associated runway information (runway length, heading and slope, A/C position relative to this selected runway).
These data are used by the Runway Overrun Prevention System (ROPS) A/C function which is a safety enhancement for manual and automatic braking modes at landing that protects against runway overrun risk.
T/TISS-TAWS includes a runway detection algorithm which purpose is to select the approached runway and to output the associated runway information (runway length, heading and slope, A/C position relative to this selected runway).
These data are used by the Runway Overrun Prevention System (ROPS) A/C function which is a safety enhancement for manual and automatic braking modes at landing that protects against runway overrun risk.
2. Interface
A. Peripherals
The TAWS receives information from the following equipment:
The TAWS receives information from the following equipment:
(1) Air Data/Inertial Reference Unit (ADIRU) 1
The T/TISS computer (TAWS function) is linked:
The T/TISS computer (TAWS function) is linked:
- to the IR portion of the ADIRU1 by a high-speed ARINC 429 bus for position (latitude and longitude), heading, pitch angle, true track angle and GPS information (altitude, longitude,altitude, verticale speed)
- To the ADR portion of the ADIRU1 by a low-speed ARINC 429 bus for airspeed and barometric parameters
The ADIRU1 is the second source of position for the T/TISS-TAWS function.
(2) Flight Management and Guidance Computer (FMGC) 1
The T/TISS computer is linked by ARINC 429 buses (two high speed and one low- speed) to the FMGC1 for position (latitude and longitude) and other parameters (date,engine out condition, etc.). FMGC1 is the third source of position for theT/TISS-TAWS function.
The T/TISS computer is linked by ARINC 429 buses (two high speed and one low- speed) to the FMGC1 for position (latitude and longitude) and other parameters (date,engine out condition, etc.). FMGC1 is the third source of position for theT/TISS-TAWS function.
(3) Flight Control Unit (FCU)
The T/TISS computer is linked by two low-speed ARINC 429 buses to the FCU (Captain and First Officer) for selected parameters (altitude, heading and track angle) and barometric reference parameters.
The T/TISS computer is linked by two low-speed ARINC 429 buses to the FCU (Captain and First Officer) for selected parameters (altitude, heading and track angle) and barometric reference parameters.
(4) Radio Altimeter (RA) transceivers
The two RA transceivers are linked to the T/TISS computer (TAWS function) via two low-speed ARINC 429 buses. In the 0 to 2500 ft range, RA is used for reactive and predictive modes. The radio altitude is an essential parameter for the TAWS to calculate the altitude blending, and to compute inhibitions. A specific monitoring logic switches RA1 to RA2 in case of failure and vice versa.
The two RA transceivers are linked to the T/TISS computer (TAWS function) via two low-speed ARINC 429 buses. In the 0 to 2500 ft range, RA is used for reactive and predictive modes. The radio altitude is an essential parameter for the TAWS to calculate the altitude blending, and to compute inhibitions. A specific monitoring logic switches RA1 to RA2 in case of failure and vice versa.
(5) Centralized Fault Display Interface Unit (CFDIU)
The T/TISS computer(TAWS function) communicates with the CFDIU via two low- speed ARINC 429 buses.
The T/TISS computer(TAWS function) communicates with the CFDIU via two low- speed ARINC 429 buses.
(6) Multi-Mode Receiver (MMR)
The T/TISS computer(TAWS function) is linked by a low-speed ARINC 429 bus to MMR for altitude and position (latitude and longitude) parameters.The MMR is the first source of position for the T/TISS-TAWS function.
The T/TISS computer(TAWS function) is also linked by a low-speed ARINC 429 bus to the MMR or the ILS for ILS indications.
The T/TISS computer(TAWS function) is linked by a low-speed ARINC 429 bus to MMR for altitude and position (latitude and longitude) parameters.The MMR is the first source of position for the T/TISS-TAWS function.
The T/TISS computer(TAWS function) is also linked by a low-speed ARINC 429 bus to the MMR or the ILS for ILS indications.
(7) Slat Flap Control Computer (SFCC)
The T/TISS computer(TAWS function)is linked by a low- speed ARINC 429 bus to the SFCC for actual flap angle parameters.
The T/TISS computer(TAWS function)is linked by a low- speed ARINC 429 bus to the SFCC for actual flap angle parameters.
(8) Weather Radar (WXR) transceivers
The T/TISS computer(TAWS function) is linked by two high-speed ARINC 429 buses to WXR 1 and 2 for hazard range parameters. Terrain and Weather cannot be displayed at the same time on the ND. When WXR is selected from FCU, Terrain is not displayed and vice versa. In case of terrain (or obstacle) alert while the WXR image is displayed on the ND, then terrain is displayed on the ND instead ofWXR (automatic alert priority management without the need to switch via the FCU).
The T/TISS computer(TAWS function) is linked by two high-speed ARINC 429 buses to WXR 1 and 2 for hazard range parameters. Terrain and Weather cannot be displayed at the same time on the ND. When WXR is selected from FCU, Terrain is not displayed and vice versa. In case of terrain (or obstacle) alert while the WXR image is displayed on the ND, then terrain is displayed on the ND instead ofWXR (automatic alert priority management without the need to switch via the FCU).
(9) Display Management Computers (DMC)
The T/TISS computer(TAWS function) sends A453 data to the three DMC via two buses in order to display terrain images and highest/lowest elevation.
The T/TISS computer(TAWS function) sends A453 data to the three DMC via two buses in order to display terrain images and highest/lowest elevation.
(10) Pin programming
Discrete pin program inputs are used:
Discrete pin program inputs are used:
- Aircraft Type
- Audio menu selection
- CRT/LCD display
- Lateral position priority
- Obstacle function
- Predictive Windshear.
3. Operation/Control and Indicating
A. General
The T/TISS-TAWS provides the following functions:
The T/TISS-TAWS provides the following functions:
- An initialization function, which manages the power up routine task, the pin-programming reading, the GCAM software initialization and the acquisition of configuration parameters.
- An input parameter acquisition function, which is dedicated to the acquisition of the different aircraft parameters and parameter computation as required, for the alerting mode operation (altitude, lateral position, RA, vertical speed, consolidated altitude).
- A flight phase assessment function whose purpose is to determine the current aircraft flight phase, in order to activate/deactivate proper basic modes and configuration predictive mode inhibition conditions.
- A terrain Collision Prediction and Alerting (CPA) function, which is aimed at predicting the potential risks of collision with terrain and providing the appropriate visual and aural alerts.
This function provides medium-term (caution), short-term (warning) and very short term (avoid) alerts when the predicted flight path is detected with an excessive closure to the terrain ahead of the aircraft.
This function uses :
*the TAWS database (terrain and airport database)
*the aircraft performance database.
This part of the CPA function agrees with the FLTA definition from TSO-C151b. The CPA also features inhibition condition in takeoff and approach phases.The CPA monitors that a "nominal" landing is being performed. If a premature descent is detected, the CPA alerting is not inhibited and will provide dedicated timely alerts. This part of the CPA fulfils TSO-C151b PDA function requirements. - An Obstacle Collision Prediction and Alerting (OCPA) function,which is aimed at predicting the potential risks of collision with obstacle and providing the appropriate visual and aural alerts.
This mode provides medium-term (caution), short-term (warning) and very short term (avoid) alerts when the predicted flight path is detected with an excessive closure to obstacles ahead of the aircraft.
This function uses:
*the obstacle database
*the aircraft performance database
*terrain collision prediction and alerting information (data and outputs) - A terrain hazard display function, which provides a display of the aircraft situation with regard to terrain hazards in order to enhance situation awareness.
- Excessive rate of descent with respect to terrain (Mode 1)
This mode, derived from DO-161A, provides a reactive short-term warning and additionally a reactive medium-term caution when the current flight path is detected with an excessive rate of descent with respect to terrain. - Excessive closure rate to terrain (Mode 2)
This mode, derived from DO-161A, provides a reactive short-term warning when the current flight path is detected with an excessive closure rate to terrain.
Mode 2 is activated when there is a significant discrepancy between the Terrain Database Elevation and the Apparent Terrain Elevation (Mean Sea Level (MSL) Altitude - Radio Altitude) computed by the T/TISS. Mode 2 implements RA overflight detection to prevent nuisance alerts in Reduced Vertical Separation Minimum (RVSM) spaces. - Excessive altitude loss after takeoff (Mode 3)
This mode, derived from DO-161A, applies to excessive altitude loss after takeoff. - Incorrect aircraft configuration with regard to terrain (Mode 4)
This mode usually applies during the landing phase of flight and results in the annunciation of an alert in the event of insufficient terrain clearance when the aircraft is not in the proper landing configuration.
Mode 4 consists of two submodes:
* Mode 4A in case of abnormal landing gear configuration,
* Mode 4B in case of abnormal landing flap configuration.
Mode 4 implements RA overflight detection to prevent nuisance alert in RVSM spaces. - Excessive glide path deviation (Mode 5)
This mode, derived from DO-161A, applies in the event of an excessive descent below the instrument glide path when making a front-course approach with the gear down. Mode 5 supports FMS Landing System (FLS) operations. - A Terrain and Obstacle hazard display function combined with Eleview which provides a display representation of the aircraft situation with regard to terrain and obstacle hazards in order to enhance situational awareness.
- An alert management function.
- A flight event/data capture function which enables the recording of GCAM flight events.
A BITE-OMS failure detection and reporting function which manages a GCAM failure detected by the operating system.
B. Dynamic Parameter Acquisition/TAWS Parameter Computation
The T/TISS acquires various parameters for TAWS operation.
The T/TISS acquires various parameters for TAWS operation.
(1) RA
(a) Filtered RA
The RA is filtered using a 0.5 second low pass filter in order to smooth frequency variations.
The RA is filtered using a 0.5 second low pass filter in order to smooth frequency variations.
(b) Radio altimeter monitoring
In T/TISS-TAWS, RA data from RA1 and RA2 is used for Reactive Modes 1 to 5 (including Mode 2 reactivation logic) and for Predictive Modes (for blending between 700 ft and 1000 ft and pure RA between 0 ft and 700 ft).
In order to prevent T/TISS-TAWS non-alerts or spurious alerts because of RA misbehaviours, two kinds of monitoring are performed in air:
In T/TISS-TAWS, RA data from RA1 and RA2 is used for Reactive Modes 1 to 5 (including Mode 2 reactivation logic) and for Predictive Modes (for blending between 700 ft and 1000 ft and pure RA between 0 ft and 700 ft).
In order to prevent T/TISS-TAWS non-alerts or spurious alerts because of RA misbehaviours, two kinds of monitoring are performed in air:
1 When both RAs are Normal Operation (NO) in air, a consistency check between the data of the 2 RAs is performed.
| if (Min (RA1, RA2) < 2200 ft) and |
| (RA1 - RA2)> 300 ft for 0,9 seconds, |
| then consistency check is Not OK. |
- If RA consistency check is OK, RA1 data is used.
- If RA consistency check is NOK, for both Reactive and Predictive Modes, higher RA value is used to prevent from spurious alerts and unwanted reactivation of Mode 2.
2 When one RA is not available (No Computed Data (NCD), or Failure Warning (FW), or no refresh, or parity error), a reasonableness check between the available RA and Computed Terrain Clearance (CTC) is performed:
| if RA < 2500 ft and |
| CTC > 5000 ft for 0.9 second, |
| then the reasonableness check is Not OK. |
NOTE: This check is only done if GPS position is used (meaning GPS lateral position pin programmed and GPS position used) in order to ensure an accurate enough CTC (if GPS position is not used, this check is not performed and RA NO value is used).
- If RA reasonableness check is OK, available RA data is used.
- If RA reasonableness check is Not OK:
RA value is not used for both Reactive and Predictive Modes (so, Reactive Modes are deactivated).
NOTE: 1: If both RAs are not available (FW or parity error or no refresh) in air, then RA is not used for Predictive and Reactive Modes (so Reactive Modes are deactivated). The FAULT legend of the GPWS/SYS pushbutton switch is on and associated ECAM messages are displayed.
2:the NCD, parity error and no refresh statuses are monitored on the ground. The FW status is not monitored on the ground.
2:the NCD, parity error and no refresh statuses are monitored on the ground. The FW status is not monitored on the ground.
(2) Computed MSL altitude
There are two options available for MSL altitude source:
There are two options available for MSL altitude source:
(a) Baro source (A/C with no GPS)
1 With Light Cold Temperature Compensation
Light Cold Temperature Compensation is present when Full Cold Temperature Compensation is disabled by pin programming.
The MSL altitude is computed per the following logic depending on barometric setting:
* QNH selected on FCU: the baro corrected altitude (label 204) from ADIRU1 is used by CPA/THD
* STD selected on FCU: the baro altitude (label 203) from ADIRU1 is used by CPA/THD
* QFE selected on FCU:
In addition, below -10 deg. C below International Standart Atmosphere (ISA), a light cold temperature correction is applied.
The graph on the following figure partially compensates for the error associated with cold temperature effects at 2.000 ft above reference altitude.
The T/TISS can accept a 100 ft error in altitude. A 100 ft error is nominal at ISA -10 deg. C and 2.000 ft indicated altitude.
Below -40 deg. C the barometric altitude source is declared invalid as it is considered as not accurate enough for the purpose of CPA alerting. The TERR STBY memo is triggered on the upper ECAM DU and Mode 2 is retrieved.
The graph on the following figure assumes -25 deg. C conditions throughout approach.
This logic tends to overcompensate at 1.000 ft by around 50 ft as a result, the error is balanced in "alerting region".
At radio altitudes below 1.000 ft, the radio altitude is blended, therefore there is less a concern of overcompensating at low altitudes.
Light Cold Temperature Compensation is present when Full Cold Temperature Compensation is disabled by pin programming.
The MSL altitude is computed per the following logic depending on barometric setting:
* QNH selected on FCU: the baro corrected altitude (label 204) from ADIRU1 is used by CPA/THD
* STD selected on FCU: the baro altitude (label 203) from ADIRU1 is used by CPA/THD
* QFE selected on FCU:
- in takeoff mode: use of the corrected baro altitude (label 204) from ADIRU1 + runway elevation
- in approach mode: use of the uncorrected baro altitude (label 203) from ADIRU1 + baro correction QNH entered by the crew via the Multipurpose Control and Display Unit (MCDU) (landing destination QNH).
T/TISS-TAWS - Takeoff/Approach Logic for MSL Altitude Computation in QFE Operation ** ON A/C NOT FOR ALL
NOTE: As soon as the aircraft has entered the approach mode, the crew has to enter the landing destination QNH on the MCDU. In case of no selection by the crew, enhanced functions are automatically inhibited (TERR STBY memo on the upper ECAM DU).
NOTE: TO phase is initialized after 4 seconds with the Air/Ground discrete from Landing Gear Control and Interface Unit 1 (LGCIU1) being "Ground".
In addition, below -10 deg. C below International Standart Atmosphere (ISA), a light cold temperature correction is applied.
The graph on the following figure partially compensates for the error associated with cold temperature effects at 2.000 ft above reference altitude.
The T/TISS can accept a 100 ft error in altitude. A 100 ft error is nominal at ISA -10 deg. C and 2.000 ft indicated altitude.
Below -40 deg. C the barometric altitude source is declared invalid as it is considered as not accurate enough for the purpose of CPA alerting. The TERR STBY memo is triggered on the upper ECAM DU and Mode 2 is retrieved.
The graph on the following figure assumes -25 deg. C conditions throughout approach.
This logic tends to overcompensate at 1.000 ft by around 50 ft as a result, the error is balanced in "alerting region".
At radio altitudes below 1.000 ft, the radio altitude is blended, therefore there is less a concern of overcompensating at low altitudes.
2 With Full Cold Temperature Compensation
Full Cold Temperature Compensation is present by default.
The MSL barometric altitude is computed based on two terms:
Full Cold Temperature Compensation is present by default.
The MSL barometric altitude is computed based on two terms:
a 1st term: Uncompensated barometric Altitude
* QNH selected on FCU: = Baro corrected altitude (label 204 from ADR bus),
* STD selected on FCU: = pressure altitude (label 203 from ADR bus),
* QFE selected on FCU:
* QNH selected on FCU: = Baro corrected altitude (label 204 from ADR bus),
* STD selected on FCU: = pressure altitude (label 203 from ADR bus),
* QFE selected on FCU:
- in takeoff mode (ref to fig 11) or during the first 5 minutes of flight: = Baro corrected altitude (label 204 from ADR bus) + Departure Airport Elevation from the GCAM
- in approach mode and 5 minutes after the timer has expired: = Baro Corrected altitude (label 204 from ADR bus) + Landing Destination Elevation (label 260 from FMS Nav bus).
b 2nd term: (Full) Cold Temperature Compensation
* STD selected on FCU: = 0 ft,
* Otherwise: = -EARP * (TAC-15°(C) + Lo * 1st term) / (273 + TAC + 0.5 * Lo * 1st term)
TAC = Outside Air Temperature measured at the aircraft altitude (label 213 from ADR bus)
Lo = Lapse rate of 0.00198 per foot
EARP = Elevation Above Reference Point,
* QFE selected on FCU: EARP = Baro corrected altitude (label 204 from ADR bus)
* QNH selected on FCU:
* STD selected on FCU: = 0 ft,
* Otherwise: = -EARP * (TAC-15°(C) + Lo * 1st term) / (273 + TAC + 0.5 * Lo * 1st term)
TAC = Outside Air Temperature measured at the aircraft altitude (label 213 from ADR bus)
Lo = Lapse rate of 0.00198 per foot
EARP = Elevation Above Reference Point,
* QFE selected on FCU: EARP = Baro corrected altitude (label 204 from ADR bus)
* QNH selected on FCU:
- for the first 5 minutes of flight: EARP = Baro corrected altitude (label 204 from ADR bus) - Uncompensated baro altitude at the time of takeoff
- ADR bus - Destination Elevation (label 260 from FMS Nav bus) (if Destination Elevation is not available, then the elevation of the nearest airport is used)
(b) GPS based logic (GPS altitude from MMR1/Global Positioning System Sensor Unit(GPSSU) )
This logic is an adaptation of the ACSS logic based on the GPS altitude:
Whatever the configuration a) or b), the above elements are inserted in a complementary filter using Vz in order to smooth potential altitude steps or pulses.
This logic is an adaptation of the ACSS logic based on the GPS altitude:
- GPS altitude used if valid and accuracy < 100 ft ("Selectable Availability" OFF assumed)
- Coasting from last valid GPS altitude based on uncorrected baro altitude (>5 min)
- Barometric data
This logic improves the accuracy, mitigates the cold temperature effects or the barometric setting mistakes.
Whatever the configuration a) or b), the above elements are inserted in a complementary filter using Vz in order to smooth potential altitude steps or pulses.
(3) Altitude blending
The blended altitude (CPA altitude) combines the computed MSL altitude and the Radio Altitude plus the terrain cell height between 1.000 feet and 700 feet.
The blending is based on a weighted average between the MSL altitude and the radio altitude plus terrain cell height, where the MSL altitude weighting decreases linearly as radio altitude decreases. For example, at a radio altitude of 850 ft, the weighting is 50 % for each variable. At 760 ft, the radio altitude based term is weighted at 80 %.
Below 700 ft, the CPA altitude is set as equal to the radio altitude plus the terrain cell height.
If a step in CPA altitude is detected (due to a terrain cell change), the filtering is performed by limiting the rate of change to 50 ft/min for 4 seconds (maximum).
The CPA altitude is used for predictive alerting only (CPA modes) and not for GPWS modes.
This feature provides some robustness against lateral position error, vertical position error (GPS altitude or Baro Altitude) and TAWS database (DB) elevation registration errors.
Effects on CPA alerting under error cases are variable and depend on the TAWS terrain profile and real terrain profile.
In the figure, the TAWS DB that is processed does not correspond to a real situation, due to erroneous lateral position or TAWS DB error. As a consequence, the A/C is computing a wrong Terrain Cell Height. If the real terrain is steeper than the terrain processed from the TAWS DB, the CPA will see the aircraft descending into the terrain (even if it is a wrong terrain) and trigger an alert.
The blended altitude (CPA altitude) combines the computed MSL altitude and the Radio Altitude plus the terrain cell height between 1.000 feet and 700 feet.
The blending is based on a weighted average between the MSL altitude and the radio altitude plus terrain cell height, where the MSL altitude weighting decreases linearly as radio altitude decreases. For example, at a radio altitude of 850 ft, the weighting is 50 % for each variable. At 760 ft, the radio altitude based term is weighted at 80 %.
Below 700 ft, the CPA altitude is set as equal to the radio altitude plus the terrain cell height.
If a step in CPA altitude is detected (due to a terrain cell change), the filtering is performed by limiting the rate of change to 50 ft/min for 4 seconds (maximum).
The CPA altitude is used for predictive alerting only (CPA modes) and not for GPWS modes.
This feature provides some robustness against lateral position error, vertical position error (GPS altitude or Baro Altitude) and TAWS database (DB) elevation registration errors.
Effects on CPA alerting under error cases are variable and depend on the TAWS terrain profile and real terrain profile.
In the figure, the TAWS DB that is processed does not correspond to a real situation, due to erroneous lateral position or TAWS DB error. As a consequence, the A/C is computing a wrong Terrain Cell Height. If the real terrain is steeper than the terrain processed from the TAWS DB, the CPA will see the aircraft descending into the terrain (even if it is a wrong terrain) and trigger an alert.
NOTE: In the worst case, when the aircraft is less than 20 seconds from Minimum Terrain Clearance Distance (MTCD), a caution alert is emitted. When it is less than 8 seconds from MTCD, a warning alert is emitted (ref Para. 3. D (1), CPA).
RA blending is not active at takeoff.
RA blending is not active at takeoff.
(4) TAWS vertical speed
The TAWS vertical speed is based on IRS Vz as a primary source, or the Barometric Altitude rate (provided by the ADIRU1). The baro altitude rate is filtered using a 3-seconds low-pass filter, IRS Vz is filtered using a 1,5- second low-pass filter. TAWS vertical speed is used by Mode 1 and CPA.
A less filtered vertical speed (namely sharp TAWS vertical speed) is used for the flight phase transition (0.5-second filtering).
The TAWS vertical speed is based on IRS Vz as a primary source, or the Barometric Altitude rate (provided by the ADIRU1). The baro altitude rate is filtered using a 3-seconds low-pass filter, IRS Vz is filtered using a 1,5- second low-pass filter. TAWS vertical speed is used by Mode 1 and CPA.
A less filtered vertical speed (namely sharp TAWS vertical speed) is used for the flight phase transition (0.5-second filtering).
(5) Lateral position (source selection)
There are three sources for horizontal position (Latitude, Longitude):
There are three sources for horizontal position (Latitude, Longitude):
| ------------------------------------------------------------------------------! |
| ! ! 1st source: ! 2nd source: ! 3rd source: ! |
| !-----------!-----------------------------!---------------------!-------------! |
| ! !Pure GPS position from: !IRS position biased !FMS position ! |
| ! ! !from the 2nd last !FMS1 ! |
| ! !T/TISS in full configuration:!good GPS reading ! ! |
| ! !MMR1 ! ! ! |
| ! ! ! ! ! |
| ! !T/TISS in TCAS+TAWS config: ! ! ! |
| ! !- MMR1 or GPSSU1 (class ! ! ! |
| ! ! 1 sensors only) and A/C in ! ! ! |
| ! ! autonomous config; ! ! ! |
| ! !- IRS1 and A/C in hybrid ! ! ! |
| ! ! configuration ! ! ! |
| !-----------!-----------------------------!---------------------!-------------! |
| ! Latitude ! Label 110 ! Label 310 ! Label 310 ! |
| !-----------!-----------------------------!---------------------!-------------! |
| ! Longitude ! Label 111 ! Label 311 ! Label 311 ! |
| !-----------!-----------------------------!---------------------!-------------! |
(a) GPS lateral position from MMR1 or GPSSU (Class 1 GPS sensors) or ADIRU1-IRS
- GPS lateral position if valid and accuracy compatible (Horizontal Figure of Merit (HFOM)< 200 m, HFOM < 550 m in cruise)biased.
(b) ADIRU1-IRS position biased from the 2nd last good GPS reading
- This coasting is performed when GPS is lost and when satellite failure detection bit is not set.
- This coasting is performed until accuracy is no more compatible (accuracy is HFOM < 200 m, HFOM < 550 m in cruise).
(c) FMS1 lateral position (A/C with no GPS)
Optionally, automatic deactivation of predictive function upon navigation high/low accuracy criteria can be activated.
When this option is configured, the predictive modes are deactivated if navigation accuracy is low.The TERR STBY memo is displayed on the upper ECAM DU and Mode 2 is retrieved.
When this option is not activated, the predictive modes are manually switched off by means of of the GPWS/TERR pushbutton switch (the OFF legend comes on) when navigation accuracy is downgraded.
Optionally, automatic deactivation of predictive function upon navigation high/low accuracy criteria can be activated.
When this option is configured, the predictive modes are deactivated if navigation accuracy is low.The TERR STBY memo is displayed on the upper ECAM DU and Mode 2 is retrieved.
When this option is not activated, the predictive modes are manually switched off by means of of the GPWS/TERR pushbutton switch (the OFF legend comes on) when navigation accuracy is downgraded.
(6) ILS back course
ILS back course is determined by comparing the calculated and selected runway heading (ILS selected runway heading + Mag Var) with True track angle. If the comparison results in a difference higher than 90 degrees, the landing gear is up, and the localizer deviation is outside +/- 3 dots, the ILS back course is set,which results in the Mode 5 alert being inhibited.
ILS back course is determined by comparing the calculated and selected runway heading (ILS selected runway heading + Mag Var) with True track angle. If the comparison results in a difference higher than 90 degrees, the landing gear is up, and the localizer deviation is outside +/- 3 dots, the ILS back course is set,which results in the Mode 5 alert being inhibited.
C. Flight Phase Assessment
(1) Air/Ground determination
(a) T/TISS air/ground determination for TAWS algorithm
The TAWS algorithm air/ground state is based on the above conditions depending on the flight phase:
The TAWS algorithm air/ground state is based on the above conditions depending on the flight phase:
1 Power on logic
the TAWS algorithm is considered "on ground" when two of the following three conditions are met:
the TAWS algorithm is considered "on ground" when two of the following three conditions are met:
- Landing gear down.
- Radio altitude less than 5 feet for more than 2 seconds.
- Ground speed less than 60 knots for more than 2 seconds.
- Takeoff state:
* TAWS not on ground.
* Landing gear up or landing flaps up.
* Radio altitude between 5 and 1500 feet for more than 2 seconds.
* Ground speed more than 80 knots for more than 2 seconds. - Cruise state:
* TAWS not on ground and not in above state
* Radio altitude more than 5 feet for more than 2 seconds
* Ground speed more than 80 knots for more than 2 seconds.
2 Transition logic
See Para. below.
See Para. below.
(2) Flight phase transition
A flight phase assessment function determines the current aircraft flight phase at power up and then checks condition for flight phase transition. Three phases exist as shown in the following figure.
Flight phases are used for reactive mode activation/deactivation and CPA inhibition rules adaptation.
A flight phase assessment function determines the current aircraft flight phase at power up and then checks condition for flight phase transition. Three phases exist as shown in the following figure.
Flight phases are used for reactive mode activation/deactivation and CPA inhibition rules adaptation.
(3) TAWS mode activation regarding flight phases
The TAWS modes are activated as follows:
The TAWS modes are activated as follows:
- CPA mode is activated in all phases
- OCPA mode is activated in all phases
- Display mode is activated in all phases
- Mode 1 is activated in takeoff or cruise/approach phases
- Mode 2 is activated in takeoff or cruise/approach phases
- Mode 3 is activated in takeoff phase
- Mode 4 is activated in cruise/approach phase
- Mode 5 is activated in cruise/approach phase
- Flight event capturing is activated in all phases
- Parameter capturing is activated in all phases
D. Predictive Modes
(1) Terrain Collision Prediction and Alerting (CPA) and Obstacle Collision Prediction and Alerting (OCPA)
(a) General
The GCAM ensures a very low rate of nuisance alerts to keep the crew confident in the generated alerts. It addresses some specific situations such as situations of normal aircraft operation according to procedures at altitudes significantly below the surrounding local terrain height (approaches in steep valleys).
The following specifications concerning the CPA mode are consistent with the TSO-C151b and take into account all the FLTA (descending/level flight), Imminent Terrain Impact (ITI) and Premature Descent Alert (PDA) requirements.
The following parameters are used for this mode:
- The Collision Prediction and Alerting function provides alerts to inform the crew that the flight path they are following is hazardous due to the presence of terrain/obstacle ahead.
The objective of the Collision Prediction and Alerting function is to warn the crew by appropriate alerts of an impending Controlled Flight Into Terrain (CFIT) in a manner which will allow them to avoid the CFIT by a timely initiation of the suitable evasive action. A pull-up evasive action is considered as the basic recovery maneuver (leading to a "Pull up" warning). If it is not possible, a turn-around recovery is indicated (leading to an "Avoid terrain" warning). - The objective of the OCPA function is to warn the crew by appropriate alerts of an impending controlled flight into obstacle in a manner which will allow them to avoid the CFIT by a timely initiation of the suitable evasive action. A pull-up evasive action is considered as the basic recovery maneuver (leading to a 'Pull up' warning). If it is not possible, a turn-around recovery is indicated (leading to an 'Avoid terrain' warning). Pin programming can deactivate this function.
The TAWS, through the GCAM, provides alerts in the following CFIT situations: - hazardous descent rate with respect to terrain/obstacle
- hazardous closure rate with respect to terrain/obstacle
- hazardous situation during a turning flight with respect to terrain/obstacle
- premature descent into terrain
- hazardous situation due to high terrain ahead that could not be cleared by a pull-up maneuver.
The GCAM ensures a very low rate of nuisance alerts to keep the crew confident in the generated alerts. It addresses some specific situations such as situations of normal aircraft operation according to procedures at altitudes significantly below the surrounding local terrain height (approaches in steep valleys).
The following specifications concerning the CPA mode are consistent with the TSO-C151b and take into account all the FLTA (descending/level flight), Imminent Terrain Impact (ITI) and Premature Descent Alert (PDA) requirements.
The following parameters are used for this mode:
| * Ground speed |
| * True track angle |
| * Sharp flight path angle |
| * Latitude |
| * Longitude |
| * Navigation accuracy |
| * Landing flaps |
| * Flap lever position |
| * Gears |
| * Static air temperature |
| * Roll angle |
| * Terrain and Airport database |
| * Obstacle database |
| * Altitude |
| * Radio Altitude (filtered) |
| * Current aircraft weight |
| * Engine-out detection |
| * Aircraft Performance Data |
| * Terrain inhibit |
| * True Airspeed |
| * GPWS inhibit. |
(b) CPA activation/de-activation logic
The following requirements describe the CPA activation/deactivation specific logic. The CPA mode is reactivated after a delay of 5 seconds if all the following conditions are met:
As soon as one parameter used by CPA mode (except for "Gears" if flap discrete is valid, "Engine out", "True Airspeed", "GPWS inhibit" and "Radio Altitude") is invalid then the mode is deactivated.
The following requirements describe the CPA activation/deactivation specific logic. The CPA mode is reactivated after a delay of 5 seconds if all the following conditions are met:
- The CPA input parameters are all valid.
- There are no cells of extracted terrain data invalid (all terrain cells extracted from a 6' by 6' terrain area with a valid quality bit).
- There are no cells of extracted terrain data missing (no terrain square missing).
- The Navigation accuracy is less than or equal to the GCAM Required Navigation Performance (RNP) (note that it is different from the RNP used for Navigation)
| --------------------------------- |
| ! Phase of operation ! GCAM RNP ! |
| !--------------------!----------! |
| ! Phase I ! 1 NM ! |
| !--------------------!----------! |
| ! Phase II ! 2 NM ! |
| !--------------------!----------! |
| ! Phase III ! 1 NM ! |
| !--------------------!----------! |
| ! Phase IV ! 0.5 NM ! |
| !--------------------!----------! |
As soon as one parameter used by CPA mode (except for "Gears" if flap discrete is valid, "Engine out", "True Airspeed", "GPWS inhibit" and "Radio Altitude") is invalid then the mode is deactivated.
(c) Principle
The generation of the alerts is based on a real-time prediction of the potential risks of collision with the terrain ahead of the aircraft performed by a comparison between a CPA clearance sensor (derived from FPA and aircraft performance database) and the terrain profile (derived from the on-board terrain database) plus Minimum Terrain Clearance Distance (MTCD).
The obstacle alerts are based upon the comparison of the OCPA clearance sensor (identical to CPA clearance sensor) with the OCPA extracted obstacles list (derived from the obstacle database) + Minimum Obstacle Clearance Distance (MOCD). This comparison is performed through the computation of the vertical distance between the clearance sensor and each obstacle of the list.
The generation of the alerts is based on a real-time prediction of the potential risks of collision with the terrain ahead of the aircraft performed by a comparison between a CPA clearance sensor (derived from FPA and aircraft performance database) and the terrain profile (derived from the on-board terrain database) plus Minimum Terrain Clearance Distance (MTCD).
The obstacle alerts are based upon the comparison of the OCPA clearance sensor (identical to CPA clearance sensor) with the OCPA extracted obstacles list (derived from the obstacle database) + Minimum Obstacle Clearance Distance (MOCD). This comparison is performed through the computation of the vertical distance between the clearance sensor and each obstacle of the list.
(d) CPA/OCPA phase of operation and MTCD/MOCD
The MTCD depends on the phase of operation/airspace definition.
Phase I : "Final" in takeoff flight phase
Phase II: "En route"
Phase III: "Terminal"
Phase IV : "Final" in cruise/approach flight phase
The basic MTCD depends on the airport airspace definition/phase of operation.
In the enroute airspace, the MTCD offset is computed as shown in the figure.
In the final airspace, the MTCD offset is computed as shown in the figure.
In the terminal airspace, the MTCD offset is computed to ensure the continuity of the offset value between the enroute airspace at 15 Nm and the final airspace at 5 Nm.
The Minimum Obstacle Clearance Distance (MOCD), is the minimum safe vertical distance between the aircraft and an obstacle when considering the CFIT situations. The MOCD is based on MTCD value.
In the current design, MOCD = MTCD, and the value of MTCD is provided to the OCPA function among the CPA input parameters.
The MTCD depends on the phase of operation/airspace definition.
Phase I : "Final" in takeoff flight phase
Phase II: "En route"
Phase III: "Terminal"
Phase IV : "Final" in cruise/approach flight phase
NOTE: The phase of operation is different from the phase of flight (ref Para.3.C.)
The MTCD is computed as follows: MTCD = basic MTCD + MTCD offset. The basic MTCD depends on the airport airspace definition/phase of operation.
- Alpha is computed to match with a 400 ft/Nm descent rate: Alpha = 3.77 deg.
- Beta is computed to match with a 500 ft/Nm descent rate: Beta = 4.70 deg.
In the enroute airspace, the MTCD offset is computed as shown in the figure.
In the final airspace, the MTCD offset is computed as shown in the figure.
In the terminal airspace, the MTCD offset is computed to ensure the continuity of the offset value between the enroute airspace at 15 Nm and the final airspace at 5 Nm.
The Minimum Obstacle Clearance Distance (MOCD), is the minimum safe vertical distance between the aircraft and an obstacle when considering the CFIT situations. The MOCD is based on MTCD value.
In the current design, MOCD = MTCD, and the value of MTCD is provided to the OCPA function among the CPA input parameters.
(e) Terrain clearance sensors
A Very Short Term clearance sensor (VST sensor),a Short Term clearance sensor (ST sensor) and a Medium Term clearance sensor (MT sensor) are computed and projected ahead of the aircraft as shown in figure.
These sensors have three parts:
The clearance sensor geometry is conservatively based on a Standard Vertical Recovery Maneuver (SVRM).
The aircraft climb performance capability is retrieved from the aircraft performance database based on the following parameters: altitude, static air temperature (converted to Delta ISA), current gross weight, flap/slat configuration, gear configuration and engine-out condition.
The raw climb capability is corrected with the (True Air Speed / Ground Speed) factor in order to take into account the rear wind component effect. This correction is only made if the wind has a degrading effect on the climb capability (the climb capability is never increased).
The operational climb capability ranges from 1.43 deg minimum to 15 deg maximum.
The source data used to generate the Aircraft Performance Database (APD) comes from the approved Airbus performance data. The climb capability as output from APD is conservative.
The sensor laterally spreads out 1.5 deg from the A/C track. When the aircraft turns, the sensor opens up into turns to determine a possible terrain conflict (up to 90 deg).
The initial sensor width is 100 m (if GPS HFOM < 100m) or 200 m otherwise (GPS HFOM > 100m FMS) to account for position uncertainty.
A Very Short Term clearance sensor (VST sensor),a Short Term clearance sensor (ST sensor) and a Medium Term clearance sensor (MT sensor) are computed and projected ahead of the aircraft as shown in figure.
These sensors have three parts:
- Flight path projection (8 seconds for the warning sensor, 20 seconds for the caution sensor)
* 1 second for the avoid sensor,
* 8 seconds for the warning sensor,
* 20 seconds for the caution sensor. - Constant 0.5g acceleration vertical maneuver
- Projection of aircraft climb capability as extracted from the aircraft performance database.
The clearance sensor geometry is conservatively based on a Standard Vertical Recovery Maneuver (SVRM).
The aircraft climb performance capability is retrieved from the aircraft performance database based on the following parameters: altitude, static air temperature (converted to Delta ISA), current gross weight, flap/slat configuration, gear configuration and engine-out condition.
The raw climb capability is corrected with the (True Air Speed / Ground Speed) factor in order to take into account the rear wind component effect. This correction is only made if the wind has a degrading effect on the climb capability (the climb capability is never increased).
The operational climb capability ranges from 1.43 deg minimum to 15 deg maximum.
The source data used to generate the Aircraft Performance Database (APD) comes from the approved Airbus performance data. The climb capability as output from APD is conservative.
The sensor laterally spreads out 1.5 deg from the A/C track. When the aircraft turns, the sensor opens up into turns to determine a possible terrain conflict (up to 90 deg).
The initial sensor width is 100 m (if GPS HFOM < 100m) or 200 m otherwise (GPS HFOM > 100m FMS) to account for position uncertainty.
1 Sensor behavior in mountainous area
Mountainous Approach Area (MAA) definition: Existence of terrain more than 2000 ft above the runway within 6NM from the threshold or airport reference point.
In MAA, the caution and warning sensor durations are linearly reduced to respectively 42 sec and 30 sec. to prevent from nuisance alerts during low altitude maneuvers.
Mountainous Approach Area (MAA) definition: Existence of terrain more than 2000 ft above the runway within 6NM from the threshold or airport reference point.
In MAA, the caution and warning sensor durations are linearly reduced to respectively 42 sec and 30 sec. to prevent from nuisance alerts during low altitude maneuvers.
2 Sensor behavior in terrain challenging aera
NOTE: Terrain challenging area applies when the nearest airport is flagged as "Terrain challenging" in the TAWS DB.
a Terrain Challenging Area Airport (TCAA) determination
Based on the known low RNP procedures (RNP AR equalor lower than <= 0.3NM), a local upgrade of the database with better resolution and a TCAA flag indication may be required.
The vast majority of the RNP AR procedures <=0.3NM do not require any upgrade of the database because they take place in location where terrain is not challenging.
Only low RNP approaches to airport surrounded by challenging terrain are eligible to go through an evaluation process in order to obtain no nuisance alert with the following hypotheses:
Otherwise, an upgrading process of the database is first performed. This upgrading process follows the best of the following options:
Based on the known low RNP procedures (RNP AR equalor lower than <= 0.3NM), a local upgrade of the database with better resolution and a TCAA flag indication may be required.
The vast majority of the RNP AR procedures <=0.3NM do not require any upgrade of the database because they take place in location where terrain is not challenging.
Only low RNP approaches to airport surrounded by challenging terrain are eligible to go through an evaluation process in order to obtain no nuisance alert with the following hypotheses:
- The central track and displaced track of +/- RNP1 (1NM) are flew.
- In approach,a 75ft vertical error will be retrieved. No vertical error is applied on the takeoff/missed approach cases.
- The climb gradient used will be set to the minimum given by the chart. A climb of 1.43 deg is to be used by default.
Otherwise, an upgrading process of the database is first performed. This upgrading process follows the best of the following options:
- 1.The terrain is updated with 15 arc-second resolution in conflicting area. Procedures are tested again. If no nuisance alert is emitted, then next steps are not performed, else another refinement has to be performed (see step 2 description).
- 2. A TCAA that encompasses the conflicting terrain is placed around the airport. Procedures are tested again. (Note that the TCAA implies a sensor reduction). If no nuisance alert is emitted, then next step (step 3) is not performed, else another refinement has to be performed (see step 3 description).
- 3. The terrain is updated with 3 arc-second resolution in conflicting area. Procedures are tested again. If no nuisance alert is emitted,then no other improvement is applied, else engineering judgement is used to analyze the issue. The criteria can be loosen to +/- 70 per cent RNP and comparison to the worse accepted case is performed. Following the result of this analysis the compliance of the procedure is assessed case by case.
b Sensor definition in TCAA
When the aircraft moves into a terrain-challenging area, the Caution and Warning sensors are reduced linearly to respectively 42 seconds and 30 seconds as shown in figures 18 and 19.
T/TISS-TAWS - Alerting Sensors with Timings in Terrain Challenging Environment ** ON A/C NOT FOR ALL
When the aircraft moves into a terrain-challenging area, the Caution and Warning sensors are reduced linearly to respectively 42 seconds and 30 seconds as shown in figures 18 and 19.
T/TISS-TAWS - Alerting Sensors with Timings in Terrain Challenging Environment ** ON A/C NOT FOR ALL NOTE: Indicated values in figure are maximum values. Depending on terrain airport configuration, the airport radius may be less than 25 NM.
(f) Premature Descent Alert (PDA)
A PDA is provided when the aircraft is descending, and the terrain of concern is below rather than in front of the aircraft.
The PDA is presented as an alternative to the Terrain Caution (ref.para.below) whenever a level-off maneuver rather than a climbing maneuver is enough to clear the situation of hazardous closure with respect to the overflown terrain/obstacle. Substitution of a Terrain Caution by a PDA is only allowed when the aircraft is close enough to the ground. Substitution is not permitted if the Terrain/Obstacle Caution was being generated prior to meet PDA generation criteria.
When PDA conditions are present, the system provides a "Too Low Terrain" aural alert only (no associated display on ND). The PDA may be followed by a CPA Terrain/Obstacle Caution and/or Warning.
the PDA is generated whenever all the following conditions are met:
A PDA is provided when the aircraft is descending, and the terrain of concern is below rather than in front of the aircraft.
The PDA is presented as an alternative to the Terrain Caution (ref.para.below) whenever a level-off maneuver rather than a climbing maneuver is enough to clear the situation of hazardous closure with respect to the overflown terrain/obstacle. Substitution of a Terrain Caution by a PDA is only allowed when the aircraft is close enough to the ground. Substitution is not permitted if the Terrain/Obstacle Caution was being generated prior to meet PDA generation criteria.
When PDA conditions are present, the system provides a "Too Low Terrain" aural alert only (no associated display on ND). The PDA may be followed by a CPA Terrain/Obstacle Caution and/or Warning.
the PDA is generated whenever all the following conditions are met:
- the Caution clearance sensor is within a vertical distance less than MTCD from the terrain profile for at least 2 seconds,
- no Terrain Caution alert was being generated,
- no alert Obstacle Caution was being generated
- the current vertical speed is negative,
- Aircraft Level-Off Altitude > Terrain Cell Height + MTCD
- Aircraft Level-Off Altitude > Obstacle Height + MTCD.
The Aircraft Level-Off Altitude is calculated by subtracting from the current aircraft altitude the loss of altitude induced by 3 seconds of current vertical speed and a 0.25 g level-off maneuver, - The Radio Altitude is invalid or the radio altitude is valid and less than:
* 1000 ft when in en-route phase,
* 750 ft when in terminal phase,
* 500 ft when in final phase.
(g) "Caution Terrain" alert
The "Caution Terrain" alert is provided whenever the crew must be informed of a hazardous closure rate with respect to the overflown terrain. When it occurs, the crew must verify the flight path, stop the descent, and correct it if required.
If any doubt exists, a climb must be performed until the caution alert stops.
The corresponding generated alert is: "Terrain Ahead" or "Caution Terrain" (FAA audio option).
When the collision prediction and alerting function is activated, the alert is generated whenever the caution sensor is within a vertical distance less than MTCD from the terrain profile for at least 2 seconds. The area of concern is displayed in solid yellow pattern on the ND.
This alert is reset when the medium-term sensor is moved away from the terrain at a distance greater than the MTCD.
The "Caution Terrain" alert is provided whenever the crew must be informed of a hazardous closure rate with respect to the overflown terrain. When it occurs, the crew must verify the flight path, stop the descent, and correct it if required.
If any doubt exists, a climb must be performed until the caution alert stops.
The corresponding generated alert is: "Terrain Ahead" or "Caution Terrain" (FAA audio option).
When the collision prediction and alerting function is activated, the alert is generated whenever the caution sensor is within a vertical distance less than MTCD from the terrain profile for at least 2 seconds. The area of concern is displayed in solid yellow pattern on the ND.
This alert is reset when the medium-term sensor is moved away from the terrain at a distance greater than the MTCD.
(h) Caution Obstacle Alert
The obstacle caution is provided whenever the crew must be informed of a hazardous closure rate with respect to obstacle(s). When it occurs,the crew must verify the flight path and correct it if required.
If any doubt exists, a climb must be performed until the obstacle caution alert stops.
The corresponding generated alert is: " Caution Obstacle " (FAA) or " Obstacle Ahead ".
When the Obstacle Collision Prediction and Alerting function is activated, the alert is generated. The obstacle of concern is displayed in solid yellow pattern on the ND.
This alert is reset when the medium-term sensor is moved away from the obstacle(s) at a distance greater than the MOCD.
The obstacle caution is provided whenever the crew must be informed of a hazardous closure rate with respect to obstacle(s). When it occurs,the crew must verify the flight path and correct it if required.
If any doubt exists, a climb must be performed until the obstacle caution alert stops.
The corresponding generated alert is: " Caution Obstacle " (FAA) or " Obstacle Ahead ".
When the Obstacle Collision Prediction and Alerting function is activated, the alert is generated. The obstacle of concern is displayed in solid yellow pattern on the ND.
This alert is reset when the medium-term sensor is moved away from the obstacle(s) at a distance greater than the MOCD.
(i) Pull up warning
The "Pull Up" warning is provided whenever an immediate vertical pull up maneuver must be initiated by the crew in order to avoid a collision with the terrain.
The corresponding generated alert is: "Terrain Ahead Pull Up" or "Terrain Terrain Pull Up" (FAA audio option).
When the collision prediction and alerting function is activated, the " Pull-up" warning is generated whenever the vertical distance between the terrain profile and the warning sensor is less than MTCD.
In such a case, an immediate vertical pull-up maneuver allows a safe recovery. The area of concern is displayed in solid red pattern on the ND.
The "Pull Up" warning is provided whenever an immediate vertical pull up maneuver must be initiated by the crew in order to avoid a collision with the terrain.
The corresponding generated alert is: "Terrain Ahead Pull Up" or "Terrain Terrain Pull Up" (FAA audio option).
When the collision prediction and alerting function is activated, the " Pull-up" warning is generated whenever the vertical distance between the terrain profile and the warning sensor is less than MTCD.
In such a case, an immediate vertical pull-up maneuver allows a safe recovery. The area of concern is displayed in solid red pattern on the ND.
(j) Obstacle warning
The obstacle pull-up warning is provided whenever an immediate vertical pull-up maneuver must be initiated by the crew in order to avoid a collision with an obstacle.
The corresponding generated alert is " Obstacle Obstacle, Pull Up, Pull Up " (FAA) or " Obstacle Ahead Pull Up ". When the Obstacle Collision Prediction and Alerting function is activated, the alert is generated whenever the short-term warning sensor is within a vertical distance less than MOCD from at least one obstacle of the OCPA obstacle list.
In such a case, an immediate vertical pull-up maneuver allows a safe recovery. The obstacle of concern is displayed in solid red pattern on the ND.
This alert is reset when the obstacle warning sensor is moved away from the obstacle at a distance greater than the MOCD as defined when the alert has been initiated, with a 2-second confirmation.
The obstacle pull-up warning is provided whenever an immediate vertical pull-up maneuver must be initiated by the crew in order to avoid a collision with an obstacle.
The corresponding generated alert is " Obstacle Obstacle, Pull Up, Pull Up " (FAA) or " Obstacle Ahead Pull Up ". When the Obstacle Collision Prediction and Alerting function is activated, the alert is generated whenever the short-term warning sensor is within a vertical distance less than MOCD from at least one obstacle of the OCPA obstacle list.
In such a case, an immediate vertical pull-up maneuver allows a safe recovery. The obstacle of concern is displayed in solid red pattern on the ND.
This alert is reset when the obstacle warning sensor is moved away from the obstacle at a distance greater than the MOCD as defined when the alert has been initiated, with a 2-second confirmation.
(k) Avoid Terrain warning
The "Avoid Terrain" warning is provided whenever the current aircraft flight path is hazardous due to the presence of high terrain which may not be cleared by a vertical pull-up maneuver given the present capability of the aircraft. Thus it requires an immediate and appropriate maneuver to be initiated by the crew in order to avoid a collision with the terrain.
This situation can occur when operating in a steep mountainous environment with an unsafe flight path, generally in view of a landing on an airport, with the aircraft operating so close to surrounding relief that execution of the standard vertical recovery maneuver will not clear the terrain.
The procedure consists first in applying the standard vertical recovery maneuver (as for previous case) and then applying an additional lateral maneuver as judged necessary. Direction is left at pilot appreciation.
The corresponding generated alert is the " Avoid Terrain ". The aural warning is always preceded by "Terrain Ahead Pull Up" or "Terrain Terrain Pull Up Pull Up" (FAA audio option) heard at least once. The area of concern is displayed in solid red-black cross-hatched pattern on the ND.
When the Collision Prediction and Alerting function is activated, the "Avoid terrain " alert is generated whenever the vertical distance between the terrain profile and the Avoid clearance sensor (very-short term sensor) is less than 30 per cent of the MTCD.
This alert is reset when the initiation condition no more exists, with a 2-second confirmation.
The "Avoid Terrain" warning is provided whenever the current aircraft flight path is hazardous due to the presence of high terrain which may not be cleared by a vertical pull-up maneuver given the present capability of the aircraft. Thus it requires an immediate and appropriate maneuver to be initiated by the crew in order to avoid a collision with the terrain.
This situation can occur when operating in a steep mountainous environment with an unsafe flight path, generally in view of a landing on an airport, with the aircraft operating so close to surrounding relief that execution of the standard vertical recovery maneuver will not clear the terrain.
The procedure consists first in applying the standard vertical recovery maneuver (as for previous case) and then applying an additional lateral maneuver as judged necessary. Direction is left at pilot appreciation.
The corresponding generated alert is the " Avoid Terrain ". The aural warning is always preceded by "Terrain Ahead Pull Up" or "Terrain Terrain Pull Up Pull Up" (FAA audio option) heard at least once. The area of concern is displayed in solid red-black cross-hatched pattern on the ND.
When the Collision Prediction and Alerting function is activated, the "Avoid terrain " alert is generated whenever the vertical distance between the terrain profile and the Avoid clearance sensor (very-short term sensor) is less than 30 per cent of the MTCD.
This alert is reset when the initiation condition no more exists, with a 2-second confirmation.
(l) Avoid Obstacle warning
The Avoid Obstacle warning is provided whenever the current aircraft flight path is hazardous due to the presence of high obstacle which may not be cleared by a vertical pull-up maneuver given the present capability of the aircraft, thus requiring an immediate appropriate maneuver to be initiated by the crew in order to avoid a collision with the obstacle.
When the Obstacle Collision Prediction and Alerting function is activated, the "Avoid Obstacle " alert is generated whenever the Obstacle Avoid clearance sensor is within a vertical distance less then 30% of the MOCD from at least one obstacle of the OCPA obstacle list.
This alert is reset when the initiation condition no more exists, extended to 2 seconds.
The Avoid Obstacle warning is provided whenever the current aircraft flight path is hazardous due to the presence of high obstacle which may not be cleared by a vertical pull-up maneuver given the present capability of the aircraft, thus requiring an immediate appropriate maneuver to be initiated by the crew in order to avoid a collision with the obstacle.
When the Obstacle Collision Prediction and Alerting function is activated, the "Avoid Obstacle " alert is generated whenever the Obstacle Avoid clearance sensor is within a vertical distance less then 30% of the MOCD from at least one obstacle of the OCPA obstacle list.
This alert is reset when the initiation condition no more exists, extended to 2 seconds.
(m) "Nominal" takeoff detection, runway convergence detection
The CPA alerts are inhibited when "nominal" takeoff conditions are detected or when runway convergence is detected in approach to avoid nuisance CPA alerts in phases of A/C operation close to a runway.
Takeoff is considered "nominal" if the following conditions are met:
The runway convergence detection is such that, if the aircraft is performing a premature descent or if the approach flight path is not safe, the CPA alerts are not inhibited and the crew is timely alerted.
This provides a predictive mode protection as long as the A/C is above 90 ft of the destination runway.
The runway convergence is detected while:
The CPA alerts are inhibited when "nominal" takeoff conditions are detected or when runway convergence is detected in approach to avoid nuisance CPA alerts in phases of A/C operation close to a runway.
Takeoff is considered "nominal" if the following conditions are met:
- Aircraft is in takeoff phase
- AND TAWS V/S is not negative for more than 2 seconds
- AND the horizontal distance to the runway threshold (G point) is less than 1.9 NM
- AND the altitude criterion is satisfied: it uses the variation of the MSL altitude (a/c height relative to runway), the track angle and the RA when available:
If track angle remains within 30 deg around the track angle captured at the phase transition to TO, RA must be > 0,22 * variation of MSL - 17, with variation of MSL < 650ft.
If the track angle becomes superior by 30 deg compared to the track angle captured at the phase transition to TO, RA must be > 0.22 * variation of MSL - 17, with variation of MSL < 400 ft.
The runway convergence detection is such that, if the aircraft is performing a premature descent or if the approach flight path is not safe, the CPA alerts are not inhibited and the crew is timely alerted.
This provides a predictive mode protection as long as the A/C is above 90 ft of the destination runway.
The runway convergence is detected while:
- Aircraft is in cruise/approach phase
- AND the gears are down or the flaps are in landing configuration
- AND the horizontal distance to the runway threshold is less than 5000 m
- AND the A/C horizontal position and altitude are within inhibition area for non TCAA environment as shown on the figure,
and for customized TCAA environment as shown on the figure. - AND A/C True Track is in the inhibition envelopes as shown in figures for non TCAA environment and for customized TCAA environment.
- AND if RA is invalid, the TAWS Vertical Speed is in the inhibition envelope as shown on the figure.
At the end of the approach, if the runway convergence is detected, the CPA alert remains inhibited while the A/C remains within 90 ft runway elevation and above the runway.
NOTE: On the ground, no CPA alert can be generated.
NOTE: If the airport is a basic airport (runway threshold coordinates are not available from TAWS DB), the CPA is deactivated if the A/C is within 1.9 NM from the Airport Reference Point (ARP) and below 900 ft above ARP elevation. The ECAM TERR STBY memo is then displayed and Mode 2 is permanently reactivated.
NOTE: A given TCAA airport, requiring a reduction in sensor length to prevent nuisance alerts prior to the landing tunnel, may not require customization of its landing tunnel and customization of its true track inhibition envelope, if no threatening terrain exists in the landing tunnel. As a consequence, customized TCAA indicates the environment where a re-design of the landing tunnel shape and/or true track inhibition envelope has to be performed. A runway by runway improvement is applied in order to ensure a minimum of 8 seconds before impact alerting (at 145 kt).
1 Horizontal inhibition
In case of customized TCAA environment, 4 segments are defined by a set of 3 angles (Alpha i) and 4 distances (Di) to delimit the envelope per side. Those parameters are defined by runway and are stored in the database.
Less than 4 segments can also be used to modify the shape of horizontal inhibition envelope.
In case of customized TCAA environment, 4 segments are defined by a set of 3 angles (Alpha i) and 4 distances (Di) to delimit the envelope per side. Those parameters are defined by runway and are stored in the database.
Less than 4 segments can also be used to modify the shape of horizontal inhibition envelope.
2 Altitude inhibition
3 Convergence criteria definition
a For non TCAA environment:
- Condition 1: when the a/c is on the same side as S, before the point G, the inhibition condition is defined as in figure.
- Condition 2: when the a/c is on the same side as N, before the point G, the inhibition condition is defined by:
-8 deg < Delta < +8 deg.
b For customized TCAA environment:
Less than 4 segments can also be used to modify the shape of the true track inhibition envelope.
- Condition 1: when the a/c is on the same side as S, before the point G, the inhibition condition is defined as in figure.
- Condition 2: when the a/c is on the same side as N, before the point G, the inhibition condition is defined by:
- Delta 4 deg < Delta < + Delta 1 deg.
Less than 4 segments can also be used to modify the shape of the true track inhibition envelope.
(2) Computation of TAWS displays
(a) General
This operational function enhances situational awareness by providing an image of terrain-related hazardous situations and obstacle hazardous situations in front of the aircraft on existing cockpit displays.
The generated image is composed of:
The following parameters are used for this function:
This operational function enhances situational awareness by providing an image of terrain-related hazardous situations and obstacle hazardous situations in front of the aircraft on existing cockpit displays.
The generated image is composed of:
- a "background display" containing several slices of terrain which represent relative altitudes between terrain elevations and predicted aircraft altitudes (terrain hazard mode)
- a display of areas of terrain, when CPA alerts are generated, that are in conflict with the aircraft predicted avoidance maneuver.
- an "obstacle display" which represents most significant obstacles to display with their slicing information and their alerting level information (information from Obstacle Hazard Display function) and obstacles in alert, that are in conflict with the aircraft (information from OCPA mode).The Obstacle function can be activated by pin-programming.
The following parameters are used for this function:
- Input information from the acquisition function:
* True Track angle * True Heading (display orientation) * Flight Path Angle and Sharp Flight Path Angle * Latitude and longitude * Navigation accuracy * Range (FO / CPT) * TAWS DB * Obstacle DB * Various information as output from CPA.
(b) Terrain/Obstacle background computation
The following figure shows display coloration NOT in alerting condition. Alerting area computation is explained in next section.
The terrain background coloration is computed by comparing terrain elevation to a reference altitude. Six slices are used to display the hazardous terrain. They appear on the display as, in the short term, surrounding terrain is identified at less than 2000 feet below the aircraft.
The reference altitude is the current aircraft altitude while in level flight or during a climb.
In descent, in order to provide some anticipated situation awareness, the reference altitude is projected 30 seconds long FPA then extended horizontally as shown in figure.
Blackout region: when the aircraft is within Terminal or the Final airspace of the nearest airport, then terrain whose elevation is less than the nearest runway elevation (or the nearest ARP elevation in case of a "basic airport") plus 200 ft is displayed in black.
The following figure shows display coloration NOT in alerting condition. Alerting area computation is explained in next section.
The terrain background coloration is computed by comparing terrain elevation to a reference altitude. Six slices are used to display the hazardous terrain. They appear on the display as, in the short term, surrounding terrain is identified at less than 2000 feet below the aircraft.
The reference altitude is the current aircraft altitude while in level flight or during a climb.
In descent, in order to provide some anticipated situation awareness, the reference altitude is projected 30 seconds long FPA then extended horizontally as shown in figure.
Blackout region: when the aircraft is within Terminal or the Final airspace of the nearest airport, then terrain whose elevation is less than the nearest runway elevation (or the nearest ARP elevation in case of a "basic airport") plus 200 ft is displayed in black.
(c) THD/OHD with Eleview
The Eleview mode is a complement of the THD and OHD modes and it can be activated or deactivated independently of the other modes. By the means of five distinct colour slices, Eleview mode provides a basic visual rendering of the surrounding relief (includes both terrain and obstacle) regardless of the aircraft altitude (4 slices for the terrain and 1 slice for representation of area of water).
The Eleview mode is a complement of the THD and OHD modes and it can be activated or deactivated independently of the other modes. By the means of five distinct colour slices, Eleview mode provides a basic visual rendering of the surrounding relief (includes both terrain and obstacle) regardless of the aircraft altitude (4 slices for the terrain and 1 slice for representation of area of water).
1 Elevation Numbers
Besides, the "lowest" and the "highest" elevation numbers within the displayed area are displayed on the navigation displays. These two numbers are displayed on the right bottom corner.
The elevation numbers correspond to the displayed terrain/obstacle on ND, taking into account the display mode and are displayed in ARC and ROSE modes. They are both displayed in hundreds of feet above sea level. The "lowest" elevation number indicates the lowest coloured terrain/obstacle cell elevation on the display. And the "highest" elevation number indicates the highest coloured terrain/obstacle cell elevation on the display.
Besides, the "lowest" and the "highest" elevation numbers within the displayed area are displayed on the navigation displays. These two numbers are displayed on the right bottom corner.
The elevation numbers correspond to the displayed terrain/obstacle on ND, taking into account the display mode and are displayed in ARC and ROSE modes. They are both displayed in hundreds of feet above sea level. The "lowest" elevation number indicates the lowest coloured terrain/obstacle cell elevation on the display. And the "highest" elevation number indicates the highest coloured terrain/obstacle cell elevation on the display.
(d) Alerting area computation
1 Terrain Alerting
When threatening terrain is detected by the CPA function (except in case of PDA alert), a corresponding area superimposed on terrain background is displayed according to the three following figures:
When threatening terrain is detected by the CPA function (except in case of PDA alert), a corresponding area superimposed on terrain background is displayed according to the three following figures:
- Are conflicting with caution sensor is flagged as a "Caution" area (solid yellow).
- Area conflicting with warning sensor is flagged as "Pull Up" area (solid red)
- Area conflicting with avoid sensor is flagged as "Avoid Terrain" area (red-black cross-hatched area).
Upon Avoid Terrain alert, alert area for all three types of alert (avoid, pull-up caution) can be depicted simultaneously on the display.
When an alert is detected, alerting area is computed and displayed 90 deg on each side of the track.
2 Obstacle Alerting
When a threatening obstacle is detected by OCPA function, a corresponding area is displayed according to the same logic as for terrain.
When a threatening obstacle is detected by OCPA function, a corresponding area is displayed according to the same logic as for terrain.
(3) TAWS database
The TAWS database has its own P/N and can be uploaded only through application of a Vendor Service Bulletin. The database P/N is visible in the GPWS LRU IDENT maintenance menu (Refer to Para. BITE test).
The T/TISS has been designed to handle the potential for corruption of the TAWS database file as an uploadable entity or when already resident in the T/TISS computer. If a corrupted TAWS DB is attempted to be uploaded, the upload will be rejected. If the TAWS database becomes corrupted after its uploading, a power on cycle will detect the memory region containing this CRC and cause the computer to fail.
The TAWS database is composed of two parts:
The TAWS database has its own P/N and can be uploaded only through application of a Vendor Service Bulletin. The database P/N is visible in the GPWS LRU IDENT maintenance menu (Refer to Para. BITE test).
The T/TISS has been designed to handle the potential for corruption of the TAWS database file as an uploadable entity or when already resident in the T/TISS computer. If a corrupted TAWS DB is attempted to be uploaded, the upload will be rejected. If the TAWS database becomes corrupted after its uploading, a power on cycle will detect the memory region containing this CRC and cause the computer to fail.
The TAWS database is composed of two parts:
(a) Worldwide coverage terrain database
The worldwide terrain elevation database has a resolution as required by TSO C151b:
Grid sets vary in resolution depending on geographic location. Higher resolution grids are used around airports. Lower resolution grids are used outside airport areas where aircraft enroute altitude makes hazardous conditions unlikely and for which detailed terrain features are not important to the flight crew.
Elements where terrain data are not available are marked as invalid. These unknown data are displayed in magenta medium density on the ND whatever the altitude.
The worldwide terrain elevation database has a resolution as required by TSO C151b:
- 3 arc-minute in Enroute Area corresponds to 3.0 NM Resolution (at the equator). This resolution is used in the definition of outside airport areas, except over the seas (is necessary) and over the polar areas.
- 30 arc-second corresponds to 0.5 NM Resolution (at the equator). This resolution is used for the definition of the standard airport areas (note that for standard airports, the radius may be extended from 21NM to maximum 30NM, depending of the surrouding terrain). It can also be used in Mountainous Approach Areas (MAA) in the external circle area (radius between 6 NM and 30 NM centered on the airport reference point).
- 15 arc-second corresponds to 0.25 NM Resolution (at the equator). This resolution is used in the definition of the MAA (terrain elevation more than 2000 feet above the airport), more precisely in a circle of 6 NM radius centered on the airport reference point. It can also be used for the TCAA environment definition.
- 3 arc-second corresponds to 0.05 NM Resolution (at the equator). This resolution is used in the definition of the TCAA environment (within 40 NM of airport). The choice of the resolution is customized by airport. Challenging areas are split into secondary blocks (6 arc-minute cell which may use the 3 arc-second resolution).
Grid sets vary in resolution depending on geographic location. Higher resolution grids are used around airports. Lower resolution grids are used outside airport areas where aircraft enroute altitude makes hazardous conditions unlikely and for which detailed terrain features are not important to the flight crew.
Elements where terrain data are not available are marked as invalid. These unknown data are displayed in magenta medium density on the ND whatever the altitude.
(b) Airport database
The airport database includes the following data:
Data for the nearest runway are extracted and processed to be used by the terrain threat detection and display processing functions. Data are extracted from the same airport database used by the terrain clearance floor functions. This database contains data on all hard-surface runways with published coordinates. The contents of the database are processed into nearest airport reference point or/and RWY threshold position, and nearest runway elevation for use by the TAWS. These data are updated when the terrain threat detection and display processing functions are performed.
The airport database also includes:
The airport database includes the following data:
- Airport runways longer than 3500 ft. worldwide
- Airport runways longer than 2000 ft. locally.
Data for the nearest runway are extracted and processed to be used by the terrain threat detection and display processing functions. Data are extracted from the same airport database used by the terrain clearance floor functions. This database contains data on all hard-surface runways with published coordinates. The contents of the database are processed into nearest airport reference point or/and RWY threshold position, and nearest runway elevation for use by the TAWS. These data are updated when the terrain threat detection and display processing functions are performed.
The airport database also includes:
- The airport type (basic, MAA or TCAA)
- G point coordinates
- Runway true bearing and runway length
- The approach angle (equals the glide slope angle if available in the source data and different from 0 deg, otherwise 0 deg).
- The index to landing tunnel customized parameters table and the customization of the convergence criteria are available.
- Radius value only for TCAA airports.
(c) Obstacle database
The obstacle database includes all available obstacles whose height (including accuracy margin) is strictly greater than 100 ft.
The same performance criteria as for terrain are applied on the obstacle DB. These accuracy criteria are superseded by DO-276 defined accuracy when sources are available. The accuracy criteria are the following:
The obstacle database includes all available obstacles whose height (including accuracy margin) is strictly greater than 100 ft.
The same performance criteria as for terrain are applied on the obstacle DB. These accuracy criteria are superseded by DO-276 defined accuracy when sources are available. The accuracy criteria are the following:
1 Horizontal accuracy:
- En route area: +/- 100 m
- Standard Airport area: +/- 100 m
2 Vertical accuracy:
- En route area: +/- 50 m
- Standard Airport area: +/- 20 m
(4) Aircraft Performance Database (APD)
Performance tables provide conservative climb rates taking into account the following parameters:
Climb performance table sources originate from approved data for integration in the TAWS APD (the part of aircraft aggregate ASBD and ACD database). Process used is similar to the FMS performance database generation process.
The APD is linked to T/TISS-TAWS operational software and its version is traced by means of LRU P/N. A performance database change leads to a T/TISS P/N change.
The T/TISS handles the potential for corruption of the APD file as an uploadable entity or when already resident in the T/TISS computer. If a corrupted APD is attempted to be uploaded, the upload will be rejected. If the APD becomes corrupted after its uploading, a power-on cycle will detect the memory region containing this CRC and cause the computer to fail.
The applicable configuration is activated via hardware pin programming. The proper application of pin-programming is checked thanks to parity calculation at each power up thus reducing the risk of an improper performance model to be used.
The activated performance model can be checked on page 1 of CURRENT STATUS in GPWS maintenance menu (Refer to Para. BITE test).
Performance tables provide conservative climb rates taking into account the following parameters:
- Aircraft weight
- Altitude
- Static Air Temperature (SAT)
- Landing gear and slat/flap configuration
- Engine out conditions.
Climb performance table sources originate from approved data for integration in the TAWS APD (the part of aircraft aggregate ASBD and ACD database). Process used is similar to the FMS performance database generation process.
The APD is linked to T/TISS-TAWS operational software and its version is traced by means of LRU P/N. A performance database change leads to a T/TISS P/N change.
The T/TISS handles the potential for corruption of the APD file as an uploadable entity or when already resident in the T/TISS computer. If a corrupted APD is attempted to be uploaded, the upload will be rejected. If the APD becomes corrupted after its uploading, a power-on cycle will detect the memory region containing this CRC and cause the computer to fail.
The applicable configuration is activated via hardware pin programming. The proper application of pin-programming is checked thanks to parity calculation at each power up thus reducing the risk of an improper performance model to be used.
The activated performance model can be checked on page 1 of CURRENT STATUS in GPWS maintenance menu (Refer to Para. BITE test).
E. Reactive Modes
(1) Mode 1: Excessive rate of descent with respect to terrain.
This mode, derived from DO-161A, provides a reactive short-term warning and additionally a reactive medium-term caution when the current flight path is detected with an excessive rate of descent with respect to terrain and provided that the CPA function is not activated.
The following parameters are used for this mode:
As soon as one parameter used by Mode 1 is invalid, then the mode is deactivated. When all input parameters used by Mode 1 become valid again, the Mode 1 is reactivated immediately.
A "Sink Rate" (Mode 1) caution is generated when the point defined by the radio altitude and the TAWS vertical speed is within normal Mode 1 caution envelope, as described in the following figures, for at least 1 second.
This alert is reset as soon as the point is detected outside this envelope.
A "Pull up" (Mode 1) warning is generated when the point defined by the radio altitude and the TAWS vertical speed is within normal Mode 1 warning envelope, as described in following figures, for at least 0.5 second.
This alert is reset as soon as the point is detected outside this envelope.
This mode, derived from DO-161A, provides a reactive short-term warning and additionally a reactive medium-term caution when the current flight path is detected with an excessive rate of descent with respect to terrain and provided that the CPA function is not activated.
The following parameters are used for this mode:
- Radio altitude (filtered)
- TAWS vertical speed
- GPWS inhibit.
As soon as one parameter used by Mode 1 is invalid, then the mode is deactivated. When all input parameters used by Mode 1 become valid again, the Mode 1 is reactivated immediately.
A "Sink Rate" (Mode 1) caution is generated when the point defined by the radio altitude and the TAWS vertical speed is within normal Mode 1 caution envelope, as described in the following figures, for at least 1 second.
This alert is reset as soon as the point is detected outside this envelope.
A "Pull up" (Mode 1) warning is generated when the point defined by the radio altitude and the TAWS vertical speed is within normal Mode 1 warning envelope, as described in following figures, for at least 0.5 second.
This alert is reset as soon as the point is detected outside this envelope.
(2) Mode 2: Excessive closure rate to terrain
Mode 2 is provided to warn the crew of excessive closure rate with the terrain. This mode is derived from DO-161A specifications for Mode 2. The following parameters are used for this mode:
As soon as one parameter used by Mode 2 is invalid, then the mode is deactivated. When all input parameters used by Mode 2 become valid again, Mode 2 is reactivated immediately.
A " Terrain Terrain " (Mode 2) caution is generated when the point defined by the radio altitude and the terrain closure rate remains at least 1 second:
The " Terrain Terrain " (Mode 2) caution alert is reset as soon as the point is detected outside envelope 2A or 2B.
A transition from " Terrain Terrain " (Mode 2) caution towards " Pull up " (Mode 2) warning is engaged if both following conditions are met:
This alert is reset as soon as the point is detected outside envelope 2A or 2B.
The Mode 2 envelopes are described in figure.
For a terrain closure rate greater than 6000 ft/min, the max value for radio altitude upper limit is computed according to the computed airspeed value, thus providing additional alerting envelope ("high speed extension" for Mode 2A, hatched area on the figure).
Mode 2 is generally deactivated in order to limit nuisance alert risks. It is reactivated if CPA is inhibited or failed or if there is a significant discrepancy (more than 200 ft) between the radio altitude and apparent terrain elevation (MSL Altitude - Altitude Terrain DB) computed by the T/TISS, as shown on the figure.
Mode 2 activation improves T/TISS-TAWS robustness with regards to lateral, vertical or database errors, while minimizing Mode 2 nuisance alerts.
Mode 2 is provided to warn the crew of excessive closure rate with the terrain. This mode is derived from DO-161A specifications for Mode 2. The following parameters are used for this mode:
- Computed Airspeed (CAS)
- Radio altitude (filtered)
- Landing flaps discrete
- Landing gears discrete
- GPWS inhibit.
As soon as one parameter used by Mode 2 is invalid, then the mode is deactivated. When all input parameters used by Mode 2 become valid again, Mode 2 is reactivated immediately.
A " Terrain Terrain " (Mode 2) caution is generated when the point defined by the radio altitude and the terrain closure rate remains at least 1 second:
- Within envelope 2A if the flaps are not in landing configuration
- Within envelope 2B in all other cases.
The " Terrain Terrain " (Mode 2) caution alert is reset as soon as the point is detected outside envelope 2A or 2B.
A transition from " Terrain Terrain " (Mode 2) caution towards " Pull up " (Mode 2) warning is engaged if both following conditions are met:
- the " Terrain Terrain " (Mode 2) caution alert has already been generated for 2 seconds
- the landing gears are not in landing configuration by the end of these 2 seconds.
This alert is reset as soon as the point is detected outside envelope 2A or 2B.
The Mode 2 envelopes are described in figure.
For a terrain closure rate greater than 6000 ft/min, the max value for radio altitude upper limit is computed according to the computed airspeed value, thus providing additional alerting envelope ("high speed extension" for Mode 2A, hatched area on the figure).
Mode 2 is generally deactivated in order to limit nuisance alert risks. It is reactivated if CPA is inhibited or failed or if there is a significant discrepancy (more than 200 ft) between the radio altitude and apparent terrain elevation (MSL Altitude - Altitude Terrain DB) computed by the T/TISS, as shown on the figure.
Mode 2 activation improves T/TISS-TAWS robustness with regards to lateral, vertical or database errors, while minimizing Mode 2 nuisance alerts.
(3) Mode 3: Excessive altitude loss after takeoff
Mode 3 is provided to warn the crew of potential hazardous loss of height after takeoff. This alert is derived from DO-161A specifications for Mode 3.
The following parameters are used for this mode:
Mode 3 is active in takeoff phase of flight.
As soon as one parameter used by Mode 3 is invalid, then the mode is deactivated.
When all input parameters used by Mode 3 become valid again, Mode 3 is reactivated immediately.
A "Don't Sink" (Mode 3) caution is generated when the point defined by the radio altitude and altitude loss is within the Mode 3 envelope for at least 1 second as described in figure.
This alert is reset:
The altitude loss is defined as the difference between the maximum TAWS altitude reached during the takeoff and the current altitude. The current altitude is given by the TAWS altitude when valid.
Mode 3 is provided to warn the crew of potential hazardous loss of height after takeoff. This alert is derived from DO-161A specifications for Mode 3.
The following parameters are used for this mode:
- Radio altitude (filtered)
- Altitude
- TAWS vertical speed
- GPWS inhibit.
Mode 3 is active in takeoff phase of flight.
As soon as one parameter used by Mode 3 is invalid, then the mode is deactivated.
When all input parameters used by Mode 3 become valid again, Mode 3 is reactivated immediately.
A "Don't Sink" (Mode 3) caution is generated when the point defined by the radio altitude and altitude loss is within the Mode 3 envelope for at least 1 second as described in figure.
This alert is reset:
- either if the point is detected outside Mode 3 envelope,
- or if the TAWS vertical speed is positive for more than 1 second while the point is still within the envelope.
The altitude loss is defined as the difference between the maximum TAWS altitude reached during the takeoff and the current altitude. The current altitude is given by the TAWS altitude when valid.
(4) Mode 4: Incorrect aircraft configuration with regard to terrain
Mode 4 is provided to warn the crew of potential hazardous aircraft height when not in a correct landing configuration.
This mode is subdivided in two submodes:
Mode 4 is active in approach phase of flight.
As soon as one parameter used by Mode 4 is invalid, then the mode is deactivated.
When all input parameters used by Mode 4 becomes valid again, the Mode 4 is reactivated immediately.
Mode 4 is provided to warn the crew of potential hazardous aircraft height when not in a correct landing configuration.
This mode is subdivided in two submodes:
- Mode 4A: Abnormal landing gear configuration, active as long as landing gear is up.
- Mode 4B: Abnormal landing flaps configuration, active only if the landing gear is down.
- Computed airspeed
- Radio altitude (filtered)
- Landing gears discrete
- Landing flaps discrete (FLP MODE inhibit PB, Flap full and Landing configuration Full selected or Flap position 3 and Landing configuration 3 selected)
- GPWS inhibit.
Mode 4 is active in approach phase of flight.
As soon as one parameter used by Mode 4 is invalid, then the mode is deactivated.
When all input parameters used by Mode 4 becomes valid again, the Mode 4 is reactivated immediately.
(a) Abnormal landing gear configuration (Mode 4A)
This alert is generated when the gears are not in landing configuration and when the point defined by the radio altitude and computed airspeed is within the Mode 4A envelope as shown in the figure.
The corresponding generated alert is the " Too Low Gear " (Mode 4) or a " Too Low Terrain " (Mode 4) caution. This alert is generated as long as the initiation condition exists.
This alert is generated when the gears are not in landing configuration and when the point defined by the radio altitude and computed airspeed is within the Mode 4A envelope as shown in the figure.
The corresponding generated alert is the " Too Low Gear " (Mode 4) or a " Too Low Terrain " (Mode 4) caution. This alert is generated as long as the initiation condition exists.
(b) Abnormal landing flaps configuration (Mode 4B)
This alert is generated when the gears are in landing configuration and flaps not in landing configuration, and when the point defined by the radio altitude and computed airspeed is within the Mode 4B envelope as shown in the figure.
The corresponding generated alerts are " Too Low Flaps " (Mode 4) or " Too Low Terrain " (Mode 4) cautions. These alerts are generated as long as the initiation condition exists.
Mode 4 (4A and 4B) is inhibited in approach phase if both flaps and gear are in landing configuration.
Once inhibited in approach phase below 500 ft., Mode 4 (4A and 4B) stops being inhibited if the Radio altitude is greater than 500 ft.
This alert is generated when the gears are in landing configuration and flaps not in landing configuration, and when the point defined by the radio altitude and computed airspeed is within the Mode 4B envelope as shown in the figure.
The corresponding generated alerts are " Too Low Flaps " (Mode 4) or " Too Low Terrain " (Mode 4) cautions. These alerts are generated as long as the initiation condition exists.
Mode 4 (4A and 4B) is inhibited in approach phase if both flaps and gear are in landing configuration.
Once inhibited in approach phase below 500 ft., Mode 4 (4A and 4B) stops being inhibited if the Radio altitude is greater than 500 ft.
(5) Mode 5 Excessive glide path deviation
Mode 5 is provided to warn the crew that the aircraft is dangerously below the glide path during a precision approach (ILS or ILS-like approach). This alert is derived from DO-161A specifications for Mode 5. The following parameters are used for this mode:
Mode 5 is active in the approach phase of flight.
As soon as one parameter used by Mode 5, except for the selected runway heading, true track angle and ILS back course, is invalid then Mode 5 is deactivated.
When all input parameters used by Mode 5, except for the selected runway heading, true track angle and ILS back course, become valid again, Mode 5 is reactivated immediately.
A "Glideslope" (Mode 5) caution is generated when:
A nominal volume level of the aural message is provided within envelope 5B and a 6 dB reduced one within envelope 5A.
This alert is inhibited if one of the following conditions is met:
An alert is cancelled by the "G/S Cancel" input. "G/S Cancel" indicates that an alert cancellation has been requested and remains active as long as the radio altitude height is between 30 and 1000 ft.
This function is deactivated on crew request, by the "G/S Inhibit" input.
This function remains deactivated as long as the "G/S Inhibit" input is set.
The pause between two "Glideslope" messages depends on the radio altitude and the glide deviation.
Mode 5 is inhibited when an FLS or FLS-Loc approach is detected (non precision approaches).
Mode 5 is provided to warn the crew that the aircraft is dangerously below the glide path during a precision approach (ILS or ILS-like approach). This alert is derived from DO-161A specifications for Mode 5. The following parameters are used for this mode:
- Radio altitude (filtered)
- Glideslope deviation
- Selected runway heading
- Track angle
- Landing gear discrete
- Localizer deviation
- ILS back course
- GPWS inhibit
- Glideslope cancel discrete for temporary inhibition (PULL UP/GPWS Pushbutton switch)
- Glideslope inhibit (G/S MODE inhibit pushbutton switch).
Mode 5 is active in the approach phase of flight.
As soon as one parameter used by Mode 5, except for the selected runway heading, true track angle and ILS back course, is invalid then Mode 5 is deactivated.
When all input parameters used by Mode 5, except for the selected runway heading, true track angle and ILS back course, become valid again, Mode 5 is reactivated immediately.
A "Glideslope" (Mode 5) caution is generated when:
- the Glideslope deviation < 0
- the point defined by the radio altitude and the absolute value of the glideslope (G/S) deviation is within Mode 5A or 5B envelope as described on the figure.
A nominal volume level of the aural message is provided within envelope 5B and a 6 dB reduced one within envelope 5A.
This alert is inhibited if one of the following conditions is met:
- the angle between the selected runway heading (if valid) and the track angle is greater than 90 deg
- the gear is up
- the localizer deviation is outside +/-3 dots
- the ILS back-course is valid and set.
An alert is cancelled by the "G/S Cancel" input. "G/S Cancel" indicates that an alert cancellation has been requested and remains active as long as the radio altitude height is between 30 and 1000 ft.
This function is deactivated on crew request, by the "G/S Inhibit" input.
This function remains deactivated as long as the "G/S Inhibit" input is set.
The pause between two "Glideslope" messages depends on the radio altitude and the glide deviation.
Mode 5 is inhibited when an FLS or FLS-Loc approach is detected (non precision approaches).
(6) Overflight detection (Mode 2 and Mode 4)
In order to prevent Mode 2 (caution and warning) or Mode 4 (caution) nuisance alerts in case of two aircraft crossing over each other when separated by 1000 ft or less, or when an aircraft is in a holding pattern separated by 1000 ft or less, Mode 4 caution alert (Too Low Terrain) and Mode 2 caution and warning alerts are inhibited.
In order to prevent Mode 2 (caution and warning) or Mode 4 (caution) nuisance alerts in case of two aircraft crossing over each other when separated by 1000 ft or less, or when an aircraft is in a holding pattern separated by 1000 ft or less, Mode 4 caution alert (Too Low Terrain) and Mode 2 caution and warning alerts are inhibited.
(a) The Mode 2 caution and warning alerts as well as the Mode 4A and Mode 4B caution alerts are inhibited when either of the following conditions are met:
1 Radio altitude transitions from NCD to a value between 800 and 1200 ft over a period of time of 175 ms or less OR,
2 Radio altitude transitions from a value greater than 1800 ft to a value between 800 and 1200 ft over a period of time of 175 ms or less.
(b) The Mode 2 caution and warning alerts as well as the Mode 4A and 4B caution alerts are enabled when either of the following conditions are met:
1 The radio altitude is less than 790 ft or,
2 The radio altitude is greater than 1210 ft.
F. Pushbutton Switches, GPWS Control Panel and ECAM Messages
(1) GPWS/FLAP MODE pushbutton switch (7WZ)
This pushbutton switch, when pressed (in) (white OFF legend on), overrides flap abnormal condition input and generates the GPWS FLAP MODE OFF message (green) in the memo area of the upper ECAM DU (Engine/Warning Display (EWD)).
This pushbutton switch, when pressed (in) (white OFF legend on), overrides flap abnormal condition input and generates the GPWS FLAP MODE OFF message (green) in the memo area of the upper ECAM DU (Engine/Warning Display (EWD)).
(2) GPWS/G/S MODE pushbutton switch (11WZ)
This pushbutton switch, when pressed (in) (white OFF legend on), inhibits the glide slope mode.
This pushbutton switch, when pressed (in) (white OFF legend on), inhibits the glide slope mode.
(3) GPWS/SYS pushbutton switch (9WZ)
(a) When the SYS pushbutton switch is pressed in (OFF legend on), all visual and aural ground proximity alerts (Modes 1 to 5) are inhibited and no T/TISS-TAWS self-test is possible .
(b) The SYS pushbutton switch provides a FAULT warning indicating that a failure in Modes 1 to 5 has been detected by the Enhanced GPWC. When the FAULT legend comes on, the following messages are displayed:
1 on the EWD, if they are not inhibited by the Flight Warning Computer (FWC):
| NAV - GPWS FAULT (amber) |
| -GPWS ........OFF (cyan) |
2 in the INOP SYS item, on the STATUS page of the SD:
A fault message is sent to the Centralized Fault Display Interface Unit (CFDIU).
| GPWS (amber) |
A fault message is sent to the Centralized Fault Display Interface Unit (CFDIU).
(4) GPWS/TERR pushbutton switch (31WZ)
(a) When the TERR pushbutton switch is pressed in (OFF legend on), the CPA and THD (predictive) functions are inhibited (visual display and audio inhibition).
It generates the TERR OFF message (green in cruise or amber otherwise) in the memo area of the EWD .
It generates the TERR OFF message (green in cruise or amber otherwise) in the memo area of the EWD .
(b) The TERR pushbutton switch provides a FAULT warning indicating that a failure of Terrain Awareness and Display (TAD) and/or Terrain Clearance Floor (TCF) functions has been detected by the Enhanced GPWC. When the FAULT legend comes on, the following messages are displayed:
1 on the EWD, if they are not inhibited by the FWC:
| NAV - GPWS TERR DET FAULT (amber) |
| -GPWS TERR ............OFF (cyan) |
2 in the INOP SYS item, on the STATUS page of the SD:
A fault message is sent to the CFDIU.
In such a case, Mode 2 is permanently reactivated.
| GPWS TERR (amber) |
A fault message is sent to the CFDIU.
In such a case, Mode 2 is permanently reactivated.
(5) GPWS/LDG FLAP 3 pushbutton switch (13WZ)
This pushbutton switch is pressed in (white ON legend on) when a landing in flap configuration 3 is intended.
The GPWS FLAP 3 message (green) is displayed in the memo area of the EWD.
This pushbutton switch is pressed in (white ON legend on) when a landing in flap configuration 3 is intended.
The GPWS FLAP 3 message (green) is displayed in the memo area of the EWD.
(6) PULL UP/GPWS (CAPT and F/O) pushbutton switches (4WZ) and (5WZ) These pushbutton switches have two functions when pressed (in):
- they cancel the glide slope alert, or
- they initiate the self-test sequence if the aircraft is on the ground.
(7) TERR ON ND (CAPT and F/O) pushbutton switches (30WZ1) and (30WZ2)
These pushbutton switches allow the crew to select or deselect the terrain/obstacle display on ND.
The ON legends indicate that terrain/obtacle data is displayed on the ND (following manual or automatic pop-up selection).
The following diagram provides the selection logic associated with these TERR ON ND pushbutton switches.
These pushbutton switches allow the crew to select or deselect the terrain/obstacle display on ND.
The ON legends indicate that terrain/obtacle data is displayed on the ND (following manual or automatic pop-up selection).
The following diagram provides the selection logic associated with these TERR ON ND pushbutton switches.
(8) Other indication (ECAM only)
When an input required for CPA/THD operation is considered invalid or unavailable (not a fault), the following memo is displayed on the ECAM:
In such a case, Mode 2 is permanently reactivated.
When an input required for CPA/THD operation is considered invalid or unavailable (not a fault), the following memo is displayed on the ECAM:
| TERR STBY (green) |
In such a case, Mode 2 is permanently reactivated.
G. EFIS Indications
The terrain is displayed on the NDs when the TERR ON ND pusbutton switches are pressed and is depicted as variable density dot patterns in green, yellow or red. The density and color change according to how close the terrain is relative to the aircraft altitude. Alert areas are depicted in a solid yellow, red or red-black crosshatched area on the ND.
Refer to Para. 3. D.(2) (THD) for coloration computation.
The following subsection shows EIS2 display cases as an example. The EIS1 display case is equivalent (only the display mask changes).
The terrain is displayed on the NDs when the TERR ON ND pusbutton switches are pressed and is depicted as variable density dot patterns in green, yellow or red. The density and color change according to how close the terrain is relative to the aircraft altitude. Alert areas are depicted in a solid yellow, red or red-black crosshatched area on the ND.
Refer to Para. 3. D.(2) (THD) for coloration computation.
The following subsection shows EIS2 display cases as an example. The EIS1 display case is equivalent (only the display mask changes).
(1) Background terrain display on NDs
In such a case, the cyan TERR indication is displayed in the bottom right corner in lieu of the TILT indication.
In such a case, the cyan TERR indication is displayed in the bottom right corner in lieu of the TILT indication.
(2) Terrain alerts
When a predictive mode (CPA) alert is triggered:
When a "Pull Up" predictive warning alert is heard, the TERR AHEAD or TERRAIN (FAA audio selected) red indication is displayed in the bottom right corner in lieu of the TILT indication.
The terrain cells of concern are displayed in solid red area on the terrain display.
When an "Avoid Terrain" predictive warning alert is heard, the TERR AHEAD or TERRAIN (FAA audio selected) red indication is displayed in the bottom right corner in lieu of the TILT indication.
An "Avoid Terrain" aural warning is always preceded at least once by "Terrain Ahead Pull Up" or "Terrain Terrain Pull Up Pull Up" (FAA audio selected).
The terrain cells of concern are displayed in red/black crosshatched area on the terrain display.
When a predictive mode (CPA) alert is triggered:
- An image of the terrain is automatically displayed on both NDs ("Pop-Up" activation), with threatening terrain appropriately depicted. This automatic activation is managed by the T/TISS-TAWS through switching relays via the TAWS pop-up output discretes.
NOTE: It is important to note that CPA premature descent alerts do not result in any change of the terrain display on NDs.
When a predictive caution alert is heard, the TERR AHEAD or TERRAIN (FAA audio selected) amber indication is displayed in the bottom right corner in lieu of the TILT indication.The terrain cells of concern are displayed in solid yellow area on the terrain display. When a "Pull Up" predictive warning alert is heard, the TERR AHEAD or TERRAIN (FAA audio selected) red indication is displayed in the bottom right corner in lieu of the TILT indication.
The terrain cells of concern are displayed in solid red area on the terrain display.
When an "Avoid Terrain" predictive warning alert is heard, the TERR AHEAD or TERRAIN (FAA audio selected) red indication is displayed in the bottom right corner in lieu of the TILT indication.
An "Avoid Terrain" aural warning is always preceded at least once by "Terrain Ahead Pull Up" or "Terrain Terrain Pull Up Pull Up" (FAA audio selected).
The terrain cells of concern are displayed in red/black crosshatched area on the terrain display.
(3) Obstacle alerts
When a predictive mode (OCPA) alert is triggered:
When a predictive mode (OCPA) alert is triggered:
- Automatic Terrain image is displayed on both NDs ("Pop-Up" activation), with obstacle threatening appropriately depicted. This automatic activation is managed by the T/TISS-TAWS through switching relays via the TAWS pop-up output discrete.
- In case of caution alert, the obstacle cells of concern are depicted in solid yellow.
In this case, OBST AHEAD (JAA audio) or OBST (FAA audio) amber indication is displayed in the bottom right corner in lieu of the TILT indication. - In case of warning alert, the obstacle cells of concern are depicted in solid red area
In this case, OBST AHEAD (JAA audio) or OBST (FAA audio) red indication is displayed in the bottom right corner in lieu of the TILT indication.
(4) Other ND messages
If an alert is on-going:
If an alert is on-going:
- TERR : The REDUCE RANGE (red) message is displayed on the center part of the NDs if the selected range is 160 NM or 320 NM.
- TERR : The CHANGE MODE (red) message is displayed on the center part of the NDs if the selected mode is PLAN or ENG (the terrain image can only be displayed with ROSE-NAV, ROSE-ILS, ROSE-VOR or ARC mode selected).
4. BITE Test
A. Self-Test
On the ground only, the T/TISS-TAWS provides self-test capability, providing an indication of the ability of the system to perform its intended functions.
The T/TISS-TAWS self-test can be initiated via the MCDU on the ground (recommended procedure) or by means of the PULL UP/GPWS pushbutton switches. When momentarily pressing the PULL UP/GPWS pushbutton switches, the self-test is annunciated, via the same audio system as the TAWS alerts.
When the self-test starts, the system provides the following aural message through the loudspeaker:
The TAWS test pattern is displayed on both NDs with ON green legend of TERR ON ND pushbutton switches on. Then the "highest" and "lowest" elevations are both set to amber "XXX" for the first 5 seconds, then respectively changed to red "290" and green "-13" until the end of the T/TISS-TAWS self-test.
The following legends come on for 4.0 seconds, go off for 2.0 seconds, come on again for approximately 4.0 seconds and then go off:
On the ground only, the T/TISS-TAWS provides self-test capability, providing an indication of the ability of the system to perform its intended functions.
The T/TISS-TAWS self-test can be initiated via the MCDU on the ground (recommended procedure) or by means of the PULL UP/GPWS pushbutton switches. When momentarily pressing the PULL UP/GPWS pushbutton switches, the self-test is annunciated, via the same audio system as the TAWS alerts.
When the self-test starts, the system provides the following aural message through the loudspeaker:
| "TERRAIN AWARENESS TEST START". |
The TAWS test pattern is displayed on both NDs with ON green legend of TERR ON ND pushbutton switches on. Then the "highest" and "lowest" elevations are both set to amber "XXX" for the first 5 seconds, then respectively changed to red "290" and green "-13" until the end of the T/TISS-TAWS self-test.
The following legends come on for 4.0 seconds, go off for 2.0 seconds, come on again for approximately 4.0 seconds and then go off:
- FAULT legend of GPWS/TERR pushbutton switch
- FAULT legend of GPWS/SYS pushbutton switch
- (on sides 1 and 2) GPWS legend (caution) of PULL UP/GPWS pushbutton switch
- (on sides 1 and 2) PULL UP legend (warning) of PULL UP/GPWS pusbutton switch.
| "TERRAIN AWARENESS SYSTEM FAIL" |
| "TERRAIN AWERENESS TEST COMPLETE" |
NOTE: If an input from an external LRU is invalid causing either the Terrain Monitor or GPWS Monitor to be activated or a pin programming error is detected, the system provides the following aural message through the loudspeakers:
If either: | "TERRAIN AWARENESS LRU PASS" |
| "REQUIRED EXTERNAL INPUT FAIL" |
| "TERRAIN AWARENESS SYSTEM FAIL" |
| "TERRAIN AWERENESS TEST COMPLETE". |
(1) an input from an external LRU is NCD or functional test, or
(2) the aircraft is at a Basic airport when the Terrain Not Available discrete is grounded,
the system provides the following aural message through the loudspeakers:
Only the following inputs will drive a Terrain Not Available output and the aural message below when NCD or FT on the ground:
If none of the above conditions are met, then the self-test passes, and the system provides the following aural alerts through the loudspeakers:
When the self-test is finished, the ON legend of the TERR ON ND pushbutton switches remains on with cyan TERR indication on the bottom right corner of the ND (either terrain background is displayed, or the display is all black depending on the aircraft location).
Press on both "ON" of TERR ON ND pushbutton switches and check that the ON legend goes off and that the TERR indication disappears on both NDs (terrain background no more displayed).
the system provides the following aural message through the loudspeakers:
| "TERRAIN AWARENESS LRU PASS" |
| "REQUIRED EXTERNAL INPUT UNAVAILABLE" |
| "TERRAIN AWARENESS SYSTEM PASS" |
| "TERRAIN AWARENESS TEST COMPLETE" |
| - Latitude |
| - Longitude |
| - Altitude |
| - Heading. |
| "TERRAIN AWARENESS SYSTEM PASS" |
| "TERRAIN AWARENESS TEST COMPLETE". |
When the self-test is finished, the ON legend of the TERR ON ND pushbutton switches remains on with cyan TERR indication on the bottom right corner of the ND (either terrain background is displayed, or the display is all black depending on the aircraft location).
Press on both "ON" of TERR ON ND pushbutton switches and check that the ON legend goes off and that the TERR indication disappears on both NDs (terrain background no more displayed).
B. CFDS
(1) Introduction
The BITE facilitates maintenance on in-service aircraft. It detects and identifies the faults related to the T/TISS-TAWS (namely GPWC in maintenance menus, ref. NOTE). The BITE of the T/TISS-TAWS is connected to the CFDIU.
The BITE:
The BITE can operate in two modes:
The BITE facilitates maintenance on in-service aircraft. It detects and identifies the faults related to the T/TISS-TAWS (namely GPWC in maintenance menus, ref. NOTE). The BITE of the T/TISS-TAWS is connected to the CFDIU.
The BITE:
- continuously transmits the T/TISS-TAWS status and its identification message to the CFDIU
- memorizes the faults which have occurred during the last 64 flight segments
- monitors data inputs from the various peripherals (FMGC1, RA1/2 transceivers, ILS1 receiver, ADIRU1, SFCC1, LGCIU1, ECAM control panel, WXR1/2 and CFDIU)
- transmits to the CFDIU the result of the tests performed
- can communicate with the CFDIU through the interactive menu.
The BITE can operate in two modes:
- normal mode (faults detected by the TAWS are sent to the CFDIU)
- interactive mode (on the ground, to get access to TAWS internal fault logs and unit status information).
NOTE: No modification has been introduced into the CFDS, therefore acces to the T/TISS-TAWS onboard maintenance interface is through the "GPWC" prompt.
(2) Fault listing
The system is able to detect the following internal and external faults:
The system is able to detect the following internal and external faults:
(a) Internal fault summary
| ------------------------------------------------------------------------------- |
| ! Reported Internal Faults ! |
| !-----------------------------------------------------------------------------! |
| ! MESSAGE ! CLASS ! ATA ! |
| !-----------------------------------------------------------------------------! |
| ! GPWC(1000SG) ! 1 ! 34-43-34 ! |
| ! GPWC(1000SG) ! 3 ! 34-43-34 ! |
| ! CAPT/FO PULL UP PB SW(4/5WZ)/GPWC(1000SG) ! 1 ! 34-48-08 ! |
| ! ECP (6WT)/GPWC(1000SG) ! 1 ! 31-61-12 ! |
| ! GPWS SYS PB SW(9WZ)/GPWC(1000SG) ! 1 ! 34-48-08 ! |
| ! GPWS TERR PB SW(31WZ)/GPWC(1000SG) ! 1 ! 34-48-08 ! |
| ! GPWC (1000SG)/FWC1/2(1WW1/2)/WXR1/2(1SQ1/2) ! 1 ! 34-43-34 ! |
| ! CAPT TERR ON ND PB SW(30WZ1)/GPWC(1000SG) ! 1 ! 34-48-08 ! |
| ! FO TERR ON ND PB SW(30WZ2)/GPWC(1000SG) ! 1 ! 34-48-08 ! |
| ! WRG: AUDIO/GPWC(1000SG) ! 3 ! 34-43-34 (1) ! |
| ! GPWS SYS PB SW LAMP(9WZ)/GPWC(1000SG) ! 3 ! 34-48-08 (1) ! |
| ! GPWS TERR PB SW LAMP(31WZ)/GPWC(1000SG) ! 3 ! 34-48-08 (1) ! |
| ! GPWS PULL UP GPWS PB SW LAMP(4/5WZ)/GPWC(100SG) ! 3 ! 34-48-08 (1) ! |
| ------------------------------------------------------------------------------- |
NOTE: (1) Displayed only if "NO" is answered on the self-test validation pages, and remain displayed until "YES" is answered on the self-test validation pages.
(b) External fault summary
| ------------------------------------------------------------------------------- |
| ! Reported External Faults ! |
| !-----------------------------------------------------------------------------! |
| ! MESSAGE ! CLASS ! ATA ! |
| !-----------------------------------------------------------------------------! |
| ! SFCC1(21CV)/GPWS FLP MOD SW(7WZ)/GPWC(1000SG) ! 1 ! 27-51-34 ! |
| ! WRG:PIN PROG/GPWC(1000SG) ! 1 ! 34-43-34 ! |
| ! LGCIU1(5GA1)/GPWC(1000SG) ! 1 ! 32-31-71 ! |
| ! LGCIU1(5GA1)/GPWC(1000SG) ! 3 ! 32-31-71 ! |
| ! LGCIU1(5GA1)/CFDIU(1TW)/GPWC(1000SG) ! 3 ! 32-31-71 ! |
| ! SFCC1 (21CV)/GPWC(1000SG) ! 3 ! 27-51-34 ! |
| ! ECP(6WT)/GPWS(1000SG) ! 1 ! 31-61-12 ! |
| ! DMC1/2/3(1WT1/2/3)GPWC(1000SG) ! 3 ! 31-61-34 ! |
| ! CFDIU(1TW)/GPWC(1000SG) ! 3 ! 31-32-34 ! |
| ! RA1(2SA1)/GPWC(1000SG) ! 1 ! 34-42-33 ! |
| ! RA1(2SA1)/GPWC(1000SG! ! 3 ! 34-42-33 ! |
| ! RA2(2SA2)/GPWC(1000SG) ! 1 ! 34-42-33 ! |
| ! RA2(2SA2)/GPWC(1000SG) ! 3 ! 34-42-33 ! |
| ! ADIRU1(1FP1)BUS IR/GPWC(1000SG) ! 1 ! 34-12-34 ! |
| ! ADIRU1(1FP1)BUS IR/GPWC(1000SG) ! 3 ! 34-12-34 ! |
| ! ADIRU1(1FP1)BUS ADR/GPWC(1000SG) ! 1 ! 34-12-34 ! |
| ! ADIRU1(1FP1)BUS ADR/GPWC(1000SG) ! 3 ! 34-12-34 ! |
| ! ILS1(40RT1)/GPWC(1000SG) ! 1 ! 34-36-00 ! |
| ! ILS1(40RT1)/GPWC(1000SG) ! 3 ! 34-36-00 ! |
| ! GPS1(40RT1)/GPWS(1000SG) ! 1 ! 34-36-31 ! |
| ! GPS1(40RT1)/GPWS(1000SG) ! 3 ! 34-36-31 ! |
| ! FMGC1(1CA1)BUS EIS/GPWC(1000SG) ! 1 ! 22-83-34 ! |
| ! FMGC1(1CA1)BUS EIS/GPWC(1000SG) ! 3 ! 22-83-34 ! |
| ! FMGC1(1CA1)BUS OWN A/GPWC(1000SG) ! 1 ! 22-83-34 ! |
| ! FMGC1(1CA1)BUS OWN A/GPWC(1000SG) ! 3 ! 22-83-34 ! |
| ! FMGC1(1CA1)BUS OWN C/GPWC(1000SG) ! 1 ! 22-83-34 ! |
| ! FMGC1(1CA1)BUS OWN C/GPWC(1000SG) ! 3 ! 22-83-34 ! |
| ! FCU(2CA) BUS 1B/GPWC(1000SG) ! 1 ! 22-81-12 ! |
| ! FCU(2CA) BUS 2B/GPWC(1000SG) ! 1 ! 22-81-12 ! |
| ! WXR1(1SQ1) BUS HAZARD/GPWC(1000SG) ! 1 ! 34-41-33 (1) ! |
| ! WXR1(1SQ1) RANGE /GPWC(1000SG) ! 3 ! 34-41-33 (1) ! |
| ! WXR2(1SQ2) BUS HAZARD/GPWC(1000SG) ! 1 ! 34-41-33 (1) ! |
| ! WXR2(1SQ2) RANGE /GPWC(1000SG) ! 3 ! 34-41-33 (1) ! |
| ! WXR CONTROL PANEL(3SQ)/GPWC(1000SG) ! 1 ! 34-41-12 (1) ! |
| ! POWER SUPPLY INTERRUPT ! 1 ! 24-00-00 ! |
| ------------------------------------------------------------------------------ |
NOTE: (1) Only if PWS is configured.
(3) Normal mode
In normal mode, the BITE cyclically monitors the status of the T/TISS-TAWS.
In case of fault detection:
In normal mode, the BITE cyclically monitors the status of the T/TISS-TAWS.
In case of fault detection:
- It transmits its information to the CFDIU during the given flight. These items of information are transmitted to the CFDIU every 100 ms by an ARINC 429 message with label 356.
(4) Interactive mode
To gain access to the BITE, it is necessary to use one MCDU (Ref. ATA 22-82-00).
All information displayed on the MCDU during the BITE TEST configuration can be printed on the printer (Ref. ATA 31-35-00).
To gain access to the BITE, it is necessary to use one MCDU (Ref. ATA 22-82-00).
All information displayed on the MCDU during the BITE TEST configuration can be printed on the printer (Ref. ATA 31-35-00).
NOTE: No modification has been introduced into the CFDS, therefore the acces to T/TISS-TAWS OMS interface is through the "GPWC" prompt.
(a) System reports and test function
The menu mode can only be activated on the ground.
This mode enables communication between the CFDIU, the MCDU and the T/TISS-TAWS BITE.
The GPWC menu contains these items :
The menu mode can only be activated on the ground.
This mode enables communication between the CFDIU, the MCDU and the T/TISS-TAWS BITE.
The GPWC menu contains these items :
| LAST LEG REPORT |
| PREVIOUS LEGS REPORT |
| LRU IDENTIFICATION |
| GROUND SCANNING |
| TROUBLE SHOOTING DATA |
| CLASS 3 FAULTS |
| GROUND REPORT |
| CURRENT STATUS |
| TEST |
(b) LAST LEG REPORT
This report contains the computer internal and external Class 1 failures recorded during the last flight. The following figure shows the sequence of menus to display these messages.
This report contains the computer internal and external Class 1 failures recorded during the last flight. The following figure shows the sequence of menus to display these messages.
(c) CLASS 3 FAULT
This report contains the last leg external Class 3 failures recorded during the last flight. The following figure shows the sequence of menus to display these messages.
This report contains the last leg external Class 3 failures recorded during the last flight. The following figure shows the sequence of menus to display these messages.
(d) PREVIOUS LEGS REPORT
The messages are identical to those shown in para.(b) but concern the last 63 last flights if failures have occurred during these flights.
The messages are identical to those shown in para.(b) but concern the last 63 last flights if failures have occurred during these flights.
(e) LRU IDENTIFICATION
This menu displays the LRU P/N and the TAWS DB P/N. Aggregate ASDB and ACD P/N as well as LRU S/N are provided for information (T/TISS-TAWS software configuration file)
This menu displays the LRU P/N and the TAWS DB P/N. Aggregate ASDB and ACD P/N as well as LRU S/N are provided for information (T/TISS-TAWS software configuration file)
(f) GROUND SCANNING
This function enables consultation of the T/TISS-TAWS failure records as defined by the component manufacturer. The T/TISS peripheral monitoring and internal cyclic tests are used in order to detect transient failures.
This function enables consultation of the T/TISS-TAWS failure records as defined by the component manufacturer. The T/TISS peripheral monitoring and internal cyclic tests are used in order to detect transient failures.
(g) GROUND REPORT
This function is used to present Class 1, 2 or 3 internal failures when they are detected on the ground. These failures differ from those displayed on the LAST LEG REPORT page. The figure shows examples of internal failures recorded on the ground by the T/TISS-TAWS system.
This function is used to present Class 1, 2 or 3 internal failures when they are detected on the ground. These failures differ from those displayed on the LAST LEG REPORT page. The figure shows examples of internal failures recorded on the ground by the T/TISS-TAWS system.
(h) TROUBLE SHOOTING DATA
This function is used to analyse the snapshot of the recorded fault to detect any software bug. Two types of data are displayed:
This function is used to analyse the snapshot of the recorded fault to detect any software bug. Two types of data are displayed:
- correlation parameters which are the date and UTC hour displayed in clear English
- snapshot data delivered in hexadecimal code or in clear messages.
(i) CURRENT STATUS
This function is used to present the value or the status of the hardware pin-programming and several discretes. Activated options are reported explicitly from pages 1 to 6 whereas pin connections are reported from pages 7 to 9.
This function is used to present the value or the status of the hardware pin-programming and several discretes. Activated options are reported explicitly from pages 1 to 6 whereas pin connections are reported from pages 7 to 9.
(5) T/TISS-TAWS functional test
A T/TISS-TAWS built-in functional test can be initiated by pressing the line key adjacent to the TEST indication on the GPWS maintenance sub-menu.
The test ends with the display of the following message on the MCDU:
Then test validation pages are displayed.
Remarks:
This short test permits to check rapidly, on the ground, the functionality of the T/TISS-TAWS and particularly the correct operation of the ND via the DMC.
In addition,it enables to check the correct operation of the synthesized voice message system.
A T/TISS-TAWS built-in functional test can be initiated by pressing the line key adjacent to the TEST indication on the GPWS maintenance sub-menu.
The test ends with the display of the following message on the MCDU:
| TEST OK or TEST FAIL |
Then test validation pages are displayed.
Remarks:
This short test permits to check rapidly, on the ground, the functionality of the T/TISS-TAWS and particularly the correct operation of the ND via the DMC.
In addition,it enables to check the correct operation of the synthesized voice message system.