DOC AIRBUS | AMM A320FAPU FIRE EXTINGUISHING - 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 extinguishing system extinguishes fires detected in the APU compartment. In flight, the crew must operate the system manually from the cockpit. On the ground, the fire and overheat detection system activates the extinguishing system automatically. On ground the fire extinguishing system is only activated by loop A.
** ON A/C NOT FOR ALL The APU fire extinguishing system extinguishes fires detected in the APU compartment. In flight, the crew must operate the system manually from the cockpit. On the ground, the fire and overheat detection system activates the extinguishing system automatically. On ground the fire extinguishing system is only activated by loop A.
2. Component Location
** ON A/C NOT FOR ALL 
APU Fire Extinguishing - Component Location| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C ALL | |||||
| 11WF | BOTTLE-APU FIRE EXTING | 314AR | 313 | 26-22-00 | |
| 12WF | CARTRIDGE-APU FIRE EXTING BOTTLE | 314AR | 313 | 26-22-00 | |
3. System Description
The APU fire-extinguishing system has one fire extinguisher bottle. The bottle contains the extinguisher agent. It is hermetically sealed and pressurized with nitrogen. A pressure switch continuously monitors the pressure in the bottle. The bottle is installed in the fuselage, forward of the APU compartment between FR78 and FR79 (the FR79 is the FWD firewall of the APU compartment).
The bottle has one discharge outlet which is sealed with a metal diaphragm. A discharge head is installed on the discharge outlet. A distribution pipe connects the discharge head to the outlet in the FWD firewall of the APU compartment. An electrically-operated explosive cartridge is installed in the discharge head. The cartridge has two squibs (squib A and squib B). When electrical power is supplied to the squibs the cartridge fires and ruptures the metal diaphragm in the bottle discharge outlet. The extinguisher agent flows through the distribution pipe directly into the APU compartment.
If one squib has a failure the other squib makes sure that the cartridge fires correctly.
The bottle also has a pressure relief device which lets the extinguisher agent flow overboard if the pressure in the bottle increases to a given level. If the pressure relief device operates the extinguisher agent flows through the overboard discharge pipe to the discharge indicator. The extinguisher agent pushes the disc out of the discharge indicator housing and flows overboard. The ejected disc shows that the fire extinguisher is no longer serviceable.
When the agent is released (into the APU compartment or overboard) the pressure switch on the bottle sends a signal to the APU FIRE panel 1WD in the panel 20VU. The DISCH legend in the AGENT pushbutton switch comes on.
** ON A/C NOT FOR ALL The APU fire-extinguishing system has one fire extinguisher bottle. The bottle contains the extinguisher agent. It is hermetically sealed and pressurized with nitrogen. A pressure switch continuously monitors the pressure in the bottle. The bottle is installed in the fuselage, forward of the APU compartment between FR78 and FR79 (the FR79 is the FWD firewall of the APU compartment).
The bottle has one discharge outlet which is sealed with a metal diaphragm. A discharge head is installed on the discharge outlet. A distribution pipe connects the discharge head to the outlet in the FWD firewall of the APU compartment. An electrically-operated explosive cartridge is installed in the discharge head. The cartridge has two squibs (squib A and squib B). When electrical power is supplied to the squibs the cartridge fires and ruptures the metal diaphragm in the bottle discharge outlet. The extinguisher agent flows through the distribution pipe directly into the APU compartment.
If one squib has a failure the other squib makes sure that the cartridge fires correctly.
The bottle also has a pressure relief device which lets the extinguisher agent flow overboard if the pressure in the bottle increases to a given level. If the pressure relief device operates the extinguisher agent flows through the overboard discharge pipe to the discharge indicator. The extinguisher agent pushes the disc out of the discharge indicator housing and flows overboard. The ejected disc shows that the fire extinguisher is no longer serviceable.
When the agent is released (into the APU compartment or overboard) the pressure switch on the bottle sends a signal to the APU FIRE panel 1WD in the panel 20VU. The DISCH legend in the AGENT pushbutton switch comes on.
4. Power Supply
The aircraft DC network supplies the APU fire-extinguishing system with electrical power. It supplies 28VDC from:
** ON A/C NOT FOR ALL The aircraft DC network supplies the APU fire-extinguishing system with electrical power. It supplies 28VDC from:
- the HOT BUS 701PP through the circuit breaker 1WF (APU FIRE SQUIB A) to the cartridge SQUIB A,
- the BUS 301PP through the circuit breaker 2WF (APU FIRE SQUIB B) to the cartridge SQUIB B,
- the HOT BUS 701PP through the circuit breaker 3WF (APU FIRE VLV CTL) to the fire emergency-stop relay 6WF,
- the BUS 301PP through the circuit breaker 4WF (APU FIRE VLV CTL) to the fire emergency-stop relay 5WF,
- the BAT BUS 301PP through the circuit breaker 30WF (AUTOEXTING) to the automatic fire-extinguishing control circuit,
- the HOT BUS 702PP through the circuit breaker 2WC (ELS/HORN/SUPPLY) to the ground crew horn 6WC.
5. Interface
The APU fire-extinguishing system has an inface with:
** ON A/C NOT FOR ALL The APU fire-extinguishing system has an inface with:
- 23-42-00 Cockpit to ground crew call system,
- 26-13-00 APU fire and overheat detection system,
- 28-29-00 APU LP fuel shut off,
- 31-52-00 FWC,
- 32-62-00 Landing gear - position information,
- 49-62-00 APU emergency shutdown.
A. Fire Extinguisher Bottle FIN: 11-WF
The primary components of the fire extinguisher bottle are:
The container is charged with the extinguisher agent and pressurized with nitrogen through the fill fitting assembly. The fill fitting assembly seals the container and has a stainless steel disc which functions as a pressure relief device. If the pressure in the container increases to 1680 psi (115.8319 bar) +120 psi (8.2737 bar) -0 psi (0.0000 bar) (equivelent to a temperature of 265 deg.F (129.44 deg.C) +20 deg.F (-6.67 deg.C)) the disc ruptures and releases the extinguisher agent.
The container has a volume of 224 in.3 (3670.71 cm3). It is charged with 5.00 lb (2.2680 kg) +0.10 lb (0.0454 kg) -0 lb (0.0000 kg) of extinguisher agent and pressurized to 600 psi (41.3685 bar) +25 psi (1.7237 bar) -0 psi (0.0000 bar).
It can operate between the ambient temperatures of -65 deg.F (-53.89 deg.C) and +250 deg.F (121.11 deg.C).
The pressure switch monitors the pressure in the container. It has a guard for protection. If the pressure in the container decreases to 200 psi (13.7895 bar) +20 psi (1.3790 bar) -20 psi (-1.3790 bar) the pressure switch closes and sends a signal to the APU FIRE panel 1WD.
The primary components of the fire extinguisher bottle are:
The container is charged with the extinguisher agent and pressurized with nitrogen through the fill fitting assembly. The fill fitting assembly seals the container and has a stainless steel disc which functions as a pressure relief device. If the pressure in the container increases to 1825 psi (125.8293 bar) +200 psi (13.7895 bar) -0 psi (0.0000 bar) (equivelent to a temperature of 250 deg.F (121.11 deg.C)) the disc ruptures and releases the extinguisher agent.
The container has a volume of 224 in.3 (3670.71 cm3). It is charged with 5.00 lb (2.2680 kg) +0.10 lb (0.0454 kg) -0 lb (0.0000 kg) of extinguisher agent and pressurized to 600 psi (41.3685 bar) +25 psi (1.7237 bar) -0 psi (0.0000 bar).
It can operate between the ambient temperatures of -65 deg.F (-53.89 deg.C) and +250 deg.F (121.11 deg.C).
The pressure switch monitors the pressure in the container. It has a guard for protection. If the pressure in the container decreases to 200 psi (13.7895 bar) +50 psi (3.4474 bar) -0 psi (0.0000 bar) the pressure switch closes and sends a signal to the APU FIRE panel 1WD.
The primary components of the fire extinguisher bottle are:
- the container,
- the discharge outlet with the metal diaphragm,
- the fill fitting assembly with the pressure relief device,
- the pressure switch with a guard,
- the identification plate.
The container is charged with the extinguisher agent and pressurized with nitrogen through the fill fitting assembly. The fill fitting assembly seals the container and has a stainless steel disc which functions as a pressure relief device. If the pressure in the container increases to 1680 psi (115.8319 bar) +120 psi (8.2737 bar) -0 psi (0.0000 bar) (equivelent to a temperature of 265 deg.F (129.44 deg.C) +20 deg.F (-6.67 deg.C)) the disc ruptures and releases the extinguisher agent.
The container has a volume of 224 in.3 (3670.71 cm3). It is charged with 5.00 lb (2.2680 kg) +0.10 lb (0.0454 kg) -0 lb (0.0000 kg) of extinguisher agent and pressurized to 600 psi (41.3685 bar) +25 psi (1.7237 bar) -0 psi (0.0000 bar).
It can operate between the ambient temperatures of -65 deg.F (-53.89 deg.C) and +250 deg.F (121.11 deg.C).
The pressure switch monitors the pressure in the container. It has a guard for protection. If the pressure in the container decreases to 200 psi (13.7895 bar) +20 psi (1.3790 bar) -20 psi (-1.3790 bar) the pressure switch closes and sends a signal to the APU FIRE panel 1WD.
The primary components of the fire extinguisher bottle are:
- the container,
- the discharge outlet with the metal diaphragm,
- the fill fitting assembly with the pressure relief device,
- the pressure switch with a guard,
- the identification plate.
The container is charged with the extinguisher agent and pressurized with nitrogen through the fill fitting assembly. The fill fitting assembly seals the container and has a stainless steel disc which functions as a pressure relief device. If the pressure in the container increases to 1825 psi (125.8293 bar) +200 psi (13.7895 bar) -0 psi (0.0000 bar) (equivelent to a temperature of 250 deg.F (121.11 deg.C)) the disc ruptures and releases the extinguisher agent.
The container has a volume of 224 in.3 (3670.71 cm3). It is charged with 5.00 lb (2.2680 kg) +0.10 lb (0.0454 kg) -0 lb (0.0000 kg) of extinguisher agent and pressurized to 600 psi (41.3685 bar) +25 psi (1.7237 bar) -0 psi (0.0000 bar).
It can operate between the ambient temperatures of -65 deg.F (-53.89 deg.C) and +250 deg.F (121.11 deg.C).
The pressure switch monitors the pressure in the container. It has a guard for protection. If the pressure in the container decreases to 200 psi (13.7895 bar) +50 psi (3.4474 bar) -0 psi (0.0000 bar) the pressure switch closes and sends a signal to the APU FIRE panel 1WD.
B. Discharge Outlet (Discharge Head)
The discharge head gives a directional flow path for the extinguisher agent. It is installed on the bottle discharge outlet with a coupling nut. Before you tighten the coupling nut you can rotate the discharge head through 360 degrees and thus align it correctly with the distribution pipe. It has a filter to make sure that unwanted material from the fired cartridge and the metal diaphragm do not enter the disrtibution pipe. The distribution pipe connects the discharge head to the discharge outlet in the forward firewall of the APU compartment.
The discharge head gives a directional flow path for the extinguisher agent. It is installed on the bottle discharge outlet with a coupling nut. Before you tighten the coupling nut you can rotate the discharge head through 360 degrees and thus align it correctly with the distribution pipe. It has a filter to make sure that unwanted material from the fired cartridge and the metal diaphragm do not enter the disrtibution pipe. The distribution pipe connects the discharge head to the discharge outlet in the forward firewall of the APU compartment.
C. Cartridge 12WF
The cartridge is installed in the discharge head. It is a high-reliability explosive device and has two squibs (squib A and squib B). When electrical power is supplied to the squibs the cartridge fires and ruptures the metal diaphragm in the bottle discharge outlet. This releases the extinguisher agent.
The cartridge is installed in the discharge head. It is a high-reliability explosive device and has two squibs (squib A and squib B). When electrical power is supplied to the squibs the cartridge fires and ruptures the metal diaphragm in the bottle discharge outlet. This releases the extinguisher agent.
D. Discharge Indicator
The discharge indicator is installed in the fuselage skin between FR78 and FR79. The overboard discharge pipe connects the discharge indicator to the pressure relief device on the fire extinguisher bottle. A red disc is installed in the discharge indicator housing. You can see the red disc if the pressure relief device on the fire extinguisher bottle is in the correct condition. If the pressure relief device operates, the extinguisher agent flows through the overboard discharge pipe to the discharge indicator. The extinguisher agent pressure pushes the red disc out of the discharge indicator housing. This shows that the pressure relief device has operated and that the bottle is no longer serviceable.
The red disc is only ejected if the pressure in the bottle is too high. If the cartridge is fired and the agent is released into the APU compartment the red disc stays in the discharge indicator housing.
The discharge indicator is installed in the fuselage skin between FR78 and FR79. The overboard discharge pipe connects the discharge indicator to the pressure relief device on the fire extinguisher bottle. A red disc is installed in the discharge indicator housing. You can see the red disc if the pressure relief device on the fire extinguisher bottle is in the correct condition. If the pressure relief device operates, the extinguisher agent flows through the overboard discharge pipe to the discharge indicator. The extinguisher agent pressure pushes the red disc out of the discharge indicator housing. This shows that the pressure relief device has operated and that the bottle is no longer serviceable.
The red disc is only ejected if the pressure in the bottle is too high. If the cartridge is fired and the agent is released into the APU compartment the red disc stays in the discharge indicator housing.
7. Operation/Control and Indicating
The APU fire-extinguishing system extinguishes fires in the APU compartment. The system operates when the APU fire and overheat detection system detects an excessive temperature or a fire in the APU compartment (Ref. AMM D/O 26-13-00-00). The system operates in the subsequent modes:
The APU fire-extinguishing system extinguishes fires in the APU compartment. The system operates when the APU fire and overheat detection system detects an excessive temperature or a fire in the APU compartment (Ref. AMM D/O 26-13-00-00). The system operates in the subsequent modes:
- APU fire extinguishing in flight,
- APU fire extinguishing on the ground.
A. APU Fire Extinguishing In Flight
In flight the crew must operate the system manually from the APU FIRE panel 20VU in the cockpit. If the FDU 13WG detects an excessive temperature or a fire in the APU compartment it starts the subsequent cockpit warnings:
APU FIRE
AGENT ........................DISCH
MASTER SW ......................OFF
LAND ASAP
To fire the cartridge you must push the AGENT pushbutton switch. When you push the AGENT pushbutton switch:
In flight the crew must operate the system manually from the APU FIRE panel 20VU in the cockpit. If the FDU 13WG detects an excessive temperature or a fire in the APU compartment it starts the subsequent cockpit warnings:
- on the APU FIRE panel 20VU the light in the APU FIRE pushbutton switch comes on,
- on the glareshield panels 130VU and 131VU the MASTER WARN lights flash,
- the Continuous Repetetive Chime (CRC) comes on,
- the ECAM upper display unit shows the message,
APU FIRE
APU FIRE P/B...................PUSH
MASTER SW ......................OFF
LAND ASAP - on the ECAM lower display unit:
the APU page comes on automatically.
- the 28VDC power supply from the circuit breakers 3WF and 4WF is connected to the fire emergency-stop relays 5WF and 6WF (this energizes the relays),
- the relays 5WF and 6WF connect the power supply from the circuit breakers 1QF and 2QF to the APU low-pressure fuel-shutoff-valve actuator 3QF (Ref. AMM D/O 28-29-00-00) (the APU low-pressure fuel-shutoff-valve 14QM closes),
- the relay 5WF also sends a signal to the APU Electronic Control Box (ECB) 59KD (Ref. AMM D/O 49-62-00-00) (the ECB 59KD starts the APU emergency shutdown sequence),
- the 28VDC power supply from the circuit breakers 1WF and 2WF is connected to the AGENT pushbutton switch 10WF (the AGENT pushbutton switch is armed),
- the white SQUIB legend in the AGENT pushbutton switch comes on,
- the FDU 13WG sends a signal to the FWC and the ECAM upper display unit shows the message,
APU FIRE
AGENT AFT 10 S................DISCH
MASTER SW ......................OFF
LAND ASAP - the automatic 10 second countdown starts. After 10 seconds the AFT 10 S indication goes off. (A 10 s delay allows the APU to slow down and increases the agent effect).
APU FIRE
AGENT ........................DISCH
MASTER SW ......................OFF
LAND ASAP
To fire the cartridge you must push the AGENT pushbutton switch. When you push the AGENT pushbutton switch:
- the 28VDC power supply from the circuit breakers 1WF and 2WF is connected to the squibs A and B in the cartridge (the cartridge fires and ruptures the diaphragm in the bottle discharge outlet),
- the extinguisher agent is released and flows into the APU compartment,
- the pressure in the bottle decreases, the pressure switch closes and sends a signal to the APU FIRE panel 20VU (the amber DISCH legend in the AGENT pushbutton switch comes on),
- the FDU 13WG sends a signal to the FWC and the ECAM upper display unit shows the message,
APU FIRE
MASTER SW ......................OFF
LAND ASAP
B. On Ground
On the ground the automatic fire-extinguishing circuit controls the extinguishing sequence. The Landing Gear Control and Interface Unit (LGCIU) 5GA1 closes the FLIGHT/GROUND relay 43WF when the landing gear is compressed.
If the FDU 13WG detects an excessive temperature or a fire in the APU compartment it starts the subsequent cockpit warnings:
The automatic fire-extinguishing circuit controls the extinguishing sequence:
On the ground the automatic fire-extinguishing circuit controls the extinguishing sequence. The Landing Gear Control and Interface Unit (LGCIU) 5GA1 closes the FLIGHT/GROUND relay 43WF when the landing gear is compressed.
If the FDU 13WG detects an excessive temperature or a fire in the APU compartment it starts the subsequent cockpit warnings:
- on the APU FIRE panel 20VU the light in the APU FIRE pushbutton switch comes on,
- on the glareshield panels 130VU and 131VU the MASTER WARN lights flash,
- the CRC comes on,
- the ECAM upper display unit shows the message,
APU FIRE
APU FIRE P/B...................PUSH
MASTER SW ......................OFF
LAND ASAP - on the ECAM lower display unit:
the APU page comes on automatically.
The automatic fire-extinguishing circuit controls the extinguishing sequence:
- the circuit breaker 30WF and the FDU 13WG energize the AUTO TIME DELAY PUSCH relay 39WF (it operates three seconds after fire warning),
- the relay 39WF energizes the HORN SUPPLY relay 4WC through the HORN OFF relay 44WF (the ground crew horn 15WC comes on),
- the relay 39WF also energizes the APU FIRE light 40WF on the external power panel 108VU (the red APU FIRE light 40WF comes on).
- the AUTO PUSH relay 34WF connects the 28VDC power supply from the circuit breakers 3WF and 4WF to the FIRE EMER STOP 1(2) relays 5WF and 6WF (this energizes the relays),
- the relays 5WF and 6WF connect the power supply from the circuit breakers 1QF and 2QF to the APU low-pressure fuel-shutoff-valve actuator 3QF (Ref. AMM D/O 28-29-00-00) (the APU low-pressure fuel-shutoff-valve 14QM closes),
- the relay 5WF also sends a signal to the APU Electronic Control Box (ECB) 59KD (Ref. AMM D/O 49-62-00-00) (the ECB 59KD starts the APU emergency shutdown sequence),
- the AUTO DISCH relay 35WF connects the 28VDC power supply from the circuit breakers 1WF and 2WF through the EXTING GND TEST relay 36WF to the squibs A and B in the cartridge (the cartridge fires and ruptures the diaphragm in the bottle discharge outlet),
- the extinguisher agent is released and flows into the APU compartment,
- the pressure in the bottle decreases, the pressure switch closes and sends a signal to the APU FIRE panel 20VU (the amber DISCH legend in the AGENT pushbutton switch comes on),
- the FDU 13WG sends a signal to the FWC and the ECAM upper display unit shows the message,
APU FIRE
MASTER SW ......................OFF
(1) Reset
When you push the APU SHUT OFF pushbutton switch 1KL or you release the APU FIRE pushbutton switch the 28VDC power supply from the circuit breaker 30WF is connected to the HORN OFF relay 44WF (this energizes the relay and the ground crew horn 15WC stops).
When the fire or overheat condition is no longer available the FDU de-energizes the AUTO TIME DELAY relay 39WF (this de-energizes all relays in the automatic fire-extinguishing circuit).
When you push the APU SHUT OFF pushbutton switch 1KL or you release the APU FIRE pushbutton switch the 28VDC power supply from the circuit breaker 30WF is connected to the HORN OFF relay 44WF (this energizes the relay and the ground crew horn 15WC stops).
When the fire or overheat condition is no longer available the FDU de-energizes the AUTO TIME DELAY relay 39WF (this de-energizes all relays in the automatic fire-extinguishing circuit).
C. APU Fire-Extinguisher Bottle-Overpressure
If there is an overpressure (overtemperature) in the fire extinguisher bottle:
If there is an overpressure (overtemperature) in the fire extinguisher bottle:
- the pressure relief device operates automatically,
- the extinguisher agent is released and flows through the overboard discharge pipe to the discharge indicator,
- the pressure of the extinguisher agent pushes the red indicator disc out of the discharge indicator housing (the ejected disc shows that the pressure relief device has operated),
- the pressure switch on the bottle transmits a signal to the AGENT pushbutton switch on the APU FIRE panel 20VU (the DISCH legend comes on).
A. Automatic-Fire Extinguishing-Ground Test
On the APU AUTO EXTING section of the overhead panel 50VU, the TEST pushbutton switch 31WF starts the test of the automatic fire-extinguishing system. This pushbutton switch operates the TEST ON relay 33WF:
When you push the RESET switch 32WF:
On the APU AUTO EXTING section of the overhead panel 50VU, the TEST pushbutton switch 31WF starts the test of the automatic fire-extinguishing system. This pushbutton switch operates the TEST ON relay 33WF:
- the ON indicator light in the TEST pushbutton switch comes on,
- the TEST ON relay 33WF connects the power supply from the circuit breaker 30WF to the EXTING GND TEST relay 38WF (this energizes the EXTING GND TEST TIME DELAY relay 37WF),
- the relay 37WF energizes the EXTING GND TEST relay 36WF which isolates the automatic squib circuit of the fire extinguishing bottle to prevent the fire bottle discharging,
- once the two relays, 38WF and 36WF, are correctly energized, the AUTO PUSH relay 34WF is energized,
- if the two relays, 38WF and 36WF, are correctly energized, after a time delay of 3 seconds the relay 39WF is energized and it energizes the AUTO DISCH relay 35WF,
- the relay 39WF also energizes the HORN SUPPLY relay 4WC through the HORN OFF relay 44WF (the ground crew horn 15WC comes on),
- the relay 39WF also energizes the APU FIRE light 40WF on the external power panel 108VU (the red APU FIRE light 40WF comes on).
- the AUTO PUSH relay 34WF connects the 28VDC power supply from the circuit breakers 3WF and 4WF to the FIRE EMER STOP 1(2) relays 5WF and 6WF (this energizes the relays),
- the relays 5WF and 6WF connect the power supply from the circuit breakers 1QF and 2QF to the APU low-pressure fuel-shutoff-valve actuator 3QF (Ref. AMM D/O 28-29-00-00) (the APU low-pressure fuel-shutoff-valve 14QM closes),
- the relay 5WF also sends a signal to the APU Electronic Control Box (ECB) 59KD (Ref. AMM D/O 49-62-00-00) (the ECB 59KD starts the APU emergency shutdown sequence),
- on the APU AUTO/EXTING panel 50VU, the OK indicator light in the TEST pushbutton switch comes on (this indicates a successful test).
When you push the RESET switch 32WF:
- the the self-holding circuit of the relay TEST ON relay 33WF is de-energized,
- all other relays are de-energized. (the fire extinguishing bottle is connected again to the automatic fire-extinguishing on ground circuit),
- the ground crew horn 15WC and the APU FIRE light 40WF go off,
- the ON and OK indicator lights go off in the TEST pushbutton switch 31WF.
- the ON indicator light in the TEST pushbutton switch comes on,
- the TEST ON relay 33WF connects the power supply from the circuit breaker 30WF to the EXTING GND TEST relay 38WF (this energizes the EXTING GND TEST TIME DELAY relay 37WF),
- the relay 37WF energizes the EXTING GND TEST relay 36WF which isolates the automatic squib circuit of the fire extinguishing bottle to prevent the fire bottle discharging,
- once the two relays, 38WF and 36WF, are correctly energized, the AUTO PUSH relay 34WF is energized,
- if the two relays, 38WF and 36WF, are correctly energized, after a time delay of 3 seconds the relay 39WF is energized and it energizes the AUTO DISCH relay 35WF,
- the relay 39WF also energizes the HORN SUPPLY relay 4WC through the HORN OFF relay 44WF (the ground crew horn 15WC comes on),
- the relay 39WF also energizes the APU FIRE light 40WF on the external power panel 108VU (the red APU FIRE light 40WF comes on).
- the AUTO PUSH relay 34WF connects the 28VDC power supply from the circuit breakers 3WF and 4WF to the FIRE EMER STOP 1(2) relays 5WF and 6WF (this energizes the relays),
- the relays 5WF and 6WF connect the power supply from the circuit breakers 1QF and 2QF to the APU low-pressure fuel-shutoff-valve actuator 3QF (Ref. AMM D/O 28-29-00-00) (the APU low-pressure fuel-shutoff-valve 14QM closes),
- the relay 5WF also sends a signal to the APU Electronic Control Box (ECB) 59KD (Ref. AMM D/O 49-62-00-00) (the ECB 59KD starts the APU emergency shutdown sequence),
- on the APU AUTO/EXTING panel 50VU, the OK indicator light in the TEST pushbutton switch comes on (this indicates a successful test).
NOTE: This test causes a spurious WARNING in ECAM (APU FIRE LOOP A FAULT) because of a FDU hardware modification.
When you push the RESET switch 32WF: - the the self-holding circuit of the relay TEST ON relay 33WF is de-energized,
- all other relays are de-energized. (the fire extinguishing bottle is connected again to the automatic fire-extinguishing on ground circuit),
- the ground crew horn 15WC and the APU FIRE light 40WF go off,
- the ON and OK indicator lights go off in the TEST pushbutton switch 31WF.
B. Squib and Discharge Test Operation
When you push the TEST pushbutton switch on the APU FIRE panel 20VU the squib and discharge test starts. The TEST switch connects each cartridge resistor in line with one relay which are installed in the APU FIRE panel 20VU. When both relays are energized the SQUIB legend of the AGENT pushbutton switch comes on. Both resistors of the cartridge function correctly.
The TEST pushbutton switch disconnects the normal pressure indication (DC GND signal) and simulates a pressure loss in the extinguisher bottle (bottle discharged). The disconnected GND signal triggers a relay via a transistor. The DISCH legend in the AGEND pushbutton switch comes on.
The test stops when the TEST pushbutton switch is released.
When you push the TEST pushbutton switch on the APU FIRE panel 20VU the squib and discharge test starts. The TEST switch connects each cartridge resistor in line with one relay which are installed in the APU FIRE panel 20VU. When both relays are energized the SQUIB legend of the AGENT pushbutton switch comes on. Both resistors of the cartridge function correctly.
The TEST pushbutton switch disconnects the normal pressure indication (DC GND signal) and simulates a pressure loss in the extinguisher bottle (bottle discharged). The disconnected GND signal triggers a relay via a transistor. The DISCH legend in the AGEND pushbutton switch comes on.
The test stops when the TEST pushbutton switch is released.