DOC AIRBUS | AMM A320FAPU FIRE AND OVERHEAT DETECTION - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The APU fire detection system operates pneumatically. It senses and gives indication of fire or overheat condition in the APU compartment with two independent fire warning loops. The detection system is has different descrimination levels for different combinations of fault and fire information.
** ON A/C NOT FOR ALL The APU fire detection system operates pneumatically. It senses and gives indication of fire or overheat condition in the APU compartment with two independent fire warning loops. The detection system is has different descrimination levels for different combinations of fault and fire information.
2. Component Location
** ON A/C NOT FOR ALL | FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C ALL | |||||
| 13WG | FDU-APU | 126 | 26-13-34 | ||
| 21WG | DETECTOR-APU FIRE (LOOP A) | 316AR | 316 | 26-13-15 | |
| 22WG | DETECTOR-APU FIRE (LOOP B) | 316AR | 316 | 26-13-15 | |
3. System Description
APU Fire and Overheat Detection - Principle Diagram ** ON A/C NOT FOR ALL
APU Fire and Overheat Detection - Principle Diagram ** ON A/C NOT FOR ALL
APU Fire and Overheat Detection - Principle Diagram ** ON A/C NOT FOR ALL APU Fire and Overheat Detection - Principle Diagram ** ON A/C NOT FOR ALL A. The detection system consists of two identical (electrically independent) loops (A and B). They are installed in the APU compartment adjacent to critical components, such as:
- fuel lines,
- starter generator,
- FCU,
- ignition box,
- turbine plenum.
(1) Pneumatic Sensor Element
The APU fire detector 21WG/22WG is a continous length, thermal sensing, pneumatic detector. Each detector has a stainless steel housed responder assembly with a length of stainless steel sensor tube permanently attached. The full assembly is welded, brazed and hermetically sealed. In the sealed responder housing are a 5-pin electrical connector and two pressure sensitive switches (alarm and integrity) in ceramic insulators. The sensor is a braze-sealed tube that contains a special core material and pressurized inert gas. The detector operates pneumatically. The APU fire detector sensing elements go along the fire walls. Dual clamps hold the sensing elements at the fire walls. The responder housings of the elements are connected to the terminal plate.
The APU fire detector 21WG/22WG is a continous length, thermal sensing, pneumatic detector. Each detector has a stainless steel housed responder assembly with a length of stainless steel sensor tube permanently attached. The full assembly is welded, brazed and hermetically sealed. In the sealed responder housing are a 5-pin electrical connector and two pressure sensitive switches (alarm and integrity) in ceramic insulators. The sensor is a braze-sealed tube that contains a special core material and pressurized inert gas. The detector operates pneumatically. The APU fire detector sensing elements go along the fire walls. Dual clamps hold the sensing elements at the fire walls. The responder housings of the elements are connected to the terminal plate.
(2) Fire Detection Unit
The Fire Detection Unit 13WG (FDU) is installed in the avionics compartment. It includes two identical and independent circuits, one for each loop. They are installed on three printed circuit boards:
The Fire Detection Unit 13WG (FDU) is installed in the avionics compartment. It includes two identical and independent circuits, one for each loop. They are installed on three printed circuit boards:
- Input/Output (I/O) circuit board,
- Loop A and Loop B circuit board,
- Micro controller circuit board.
(3) APU Fire Panel
The ENG/APU FIRE panel 1WD is on the cockpit overhead panel (20VU). The middle part is related to the APU fire detection and includes:
The ENG/APU FIRE panel 1WD is on the cockpit overhead panel (20VU). The middle part is related to the APU fire detection and includes:
- an APU FIRE pushbutton with a red integral warning light. It is guarded red.
- a TEST pushbutton for a manual system test,
- an AGENT pushbutton with a white integral light SQUIB and an amber light DISCH. (Ref. AMM D/O 26-22-00-00)
4. Interface
APU Fire and Overheat Detection - Principle Diagram ** ON A/C NOT FOR ALL
APU Fire and Overheat Detection - Principle Diagram ** ON A/C NOT FOR ALL
The APU Fire Detection System has interfaces with these systems:
** ON A/C NOT FOR ALL APU Fire and Overheat Detection - Principle Diagram ** ON A/C NOT FOR ALL APU Fire and Overheat Detection - Principle Diagram ** ON A/C NOT FOR ALL - electrical power, (Ref. AMM D/O 24-00-00-00)
- APU fire extinguishing WF, (Ref. AMM D/O 26-22-00-00)
- Centralized Fault Display Interface (CFDUI) TW, (Ref. AMM D/O 31-32-00-00)
- FWS - Acquisition/Interface WW, (Ref. AMM D/O 31-52-00-00)
- Steering GB, (Ref 32-50-00)
- Annunciator Light Test and Dimming LP, (Ref. AMM D/O 33-14-00-00)
5. Operation
(1) Fire Warnings
(a) Fire warning conditions
Fire warnings are shown on the Fire Panel, ECAM and Master Warning Lights (also a repetetive chime). The warnings come into view at loop conditions:
Fire warnings are shown on the Fire Panel, ECAM and Master Warning Lights (also a repetetive chime). The warnings come into view at loop conditions:
- Fire A and Fire B,
- Fire A and Fault B,
- Fault A and Fire B,
- Fault A and Fault B in 5 sec.
(b) Fire warnings on ground
On fire control panel 20VU:
On fire control panel 20VU:
- the red light in the APU FIRE pushbutton switch comes on,
- the red light in the two MASTER WARNING pushbuttons flash,
- a repetetive chime sounds.
- the red APU FIRE indication light comes on,
- the external horn sounds.
(c) Fire warnings in flight
On fire control panel 20VU:
On fire control panel 20VU:
- the red light in the APU FIRE pushbutton switch comes on.
- the red light in the two MASTER WARNING pushbuttons flash,
- a repetetive chime sounds.
(d) Messages
On ECAM engine and warning display, the following are shown:
On ECAM engine and warning display, the following are shown:
- APU FIRE,
- APU FIRE P/B ... PUSH,
- AGENT AFT 10 S ... DISCH (automatic countdown),
- MASTER SW ... OFF,
- APU page is shown automatically.
(2) Loop Fault Warnings
(a) Loop fault warnings are supplied, when one loop has:
- a fault in the detector or in the detection circuit,
- an electrical power failure,
- a fire signal for more than 15 sec.
(b) Loop Fault message on ECAM engine and warning display:
- FIRE APU LOOP A or B FAULT.
(3) Detector Fault Warnings
(a) APU detector fault warning is supplied when both loops are faulty.
(b) Detector fault warnings on glareshield 130VU and 131VU:
- the amber light in the two MASTER CAUTION pushbuttons flash,
- a single chime sounds.
(c) Message on ECAM engine and warning display:
- FIRE APU DET FAULT.
(4) System Test
A test pushbutton does a check for integrity of:
A test pushbutton does a check for integrity of:
- fire detection loop A and B,
- FDU,
- indications,
- warnings,
- associated wirings,
- fire extinguisher bottle, (Ref. AMM D/O 26-22-00-00)
B. Component Operation
(1) Fire Sensor Elements
Increased overall or local temperature causes a fire signal in each sensor element.
Increased overall or local temperature causes a fire signal in each sensor element.
(a) Increased overall temperature
The detector element operates with pressure. A rise of the temperature increases the pressure in the detector. The sensor tube contains a fixed volume of inert helium gas. If the sensor senses an overall temperature increase, its internal gas pressure increases proportionally. When the alarm temperature (pressure) is reached, it closes the pressure actuated alarm switch. The point to find an overheat of the entire area is between 202 DEG.C (395.60 DEG.F) and 178 DEG.C (352.40 DEG.F).
The detector element operates with pressure. A rise of the temperature increases the pressure in the detector. The sensor tube contains a fixed volume of inert helium gas. If the sensor senses an overall temperature increase, its internal gas pressure increases proportionally. When the alarm temperature (pressure) is reached, it closes the pressure actuated alarm switch. The point to find an overheat of the entire area is between 202 DEG.C (395.60 DEG.F) and 178 DEG.C (352.40 DEG.F).
(b) Increased local temperature
A separate capability for local sensing is built into the detector. A local high-intensity temperature, such as fire, gives an alarm. The sensor elements central core contains along its entire length stored active gas. This is additional to the fixed volume of inert gas in the sensor. The central core can release an extremely large volume of gas. This happens when any short section of the sensor is heated between 512 DEG.C (953.60 DEG.F) and 452 DEG.C (845.60 DEG.F).
The increased pressure operates the alarm switch. This sorption-desorption process is completely reversible and can be done repeatly.
A separate capability for local sensing is built into the detector. A local high-intensity temperature, such as fire, gives an alarm. The sensor elements central core contains along its entire length stored active gas. This is additional to the fixed volume of inert gas in the sensor. The central core can release an extremely large volume of gas. This happens when any short section of the sensor is heated between 512 DEG.C (953.60 DEG.F) and 452 DEG.C (845.60 DEG.F).
The increased pressure operates the alarm switch. This sorption-desorption process is completely reversible and can be done repeatly.
(c) Integrity Detection
The pressure of the ambient inert gas holds the integrity switch in the closed position. In the event of gas pressure loss, the switch opens and generates a loop fault signal.
The pressure of the ambient inert gas holds the integrity switch in the closed position. In the event of gas pressure loss, the switch opens and generates a loop fault signal.
(a) Dual Loop Detection
During normal conditions (no fault, no fire, no tests) the input monitoring voltage is higher than the integrity fault threshold.
It is less than the contamination fault and fire thresholds. Any fault at the sensing element/responder level (integrity switch opens) or a loss of the electrical signals increases the resistance. The voltage decreases and makes a loop inop signal.
A responder fire detection closes the alarm switch. This causes a voltage higher than the threshold of contamination fault and fire comparators. When both inputs to the exclusive OR gate are high, its output is low and stops the fault output. Fire output is only energized, if the condition from the second loop are correct. The conditions are:
During normal conditions (no fault, no fire, no tests) the input monitoring voltage is higher than the integrity fault threshold.
It is less than the contamination fault and fire thresholds. Any fault at the sensing element/responder level (integrity switch opens) or a loss of the electrical signals increases the resistance. The voltage decreases and makes a loop inop signal.
A responder fire detection closes the alarm switch. This causes a voltage higher than the threshold of contamination fault and fire comparators. When both inputs to the exclusive OR gate are high, its output is low and stops the fault output. Fire output is only energized, if the condition from the second loop are correct. The conditions are:
- fire,
- fire within 5 s.
- second loop inop.
(b) Input/Output circuit
The FDU creates a fire warning signal in channel A and B, if one of these conditions appear:
The FDU creates a fire warning signal in channel A and B, if one of these conditions appear:
- Fire A and Fire B,
- Fire A and Fault B,
- Fault A and Fire B,
- Fault A and Fault B within 5 s.
- electrical failure (loss of power, plug not connected),
- fault in a detector,
- failure in the detection circuit,
- detection of a single loop fire for greater than 15 s. while the other loop is is normal.
(c) Controller circuit
The software monitors both detection loops and reports all failures to the CFDU. The software functions are:
The software monitors both detection loops and reports all failures to the CFDU. The software functions are:
- perform self test whenever power is first energized,
- isolate all detector and loop circuit failures and memorize in non volatile memory,
- continuously transmit current and/or previous system status on the ARINC 429 bus,
- perform built in test and transmit the test results on ARINC 429 bus,
- verify the fire tests circuitry when it is activated.
6. Test
A TEST pushbutton allows a check of the two detection loops and the fire warning circuit. A voltage across both loops simulates a fire signal and gives an alarm output. When the fire warnings (Ref. Para 5.A (1) fire warnings) come on, the result of this test is correct. The fire detection is operative.
A TEST pushbutton allows a check of the two detection loops and the fire warning circuit. A voltage across both loops simulates a fire signal and gives an alarm output. When the fire warnings (Ref. Para 5.A (1) fire warnings) come on, the result of this test is correct. The fire detection is operative.
NOTE: When the aircraft supply is from batteries, the APU fire pushbutton test shows only the status of the fire loop A but not the status of the fire loop B.