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After 10 seconds the ECAM upper display unit shows the message, 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),
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the extinguisher agent is released and flows into the APU compartment,
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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),
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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 (Ref. Fig. 003) 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,
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the CRC comes on,
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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),
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the relay 39WF energizes the HORN SUPPLY relay 4WC through the HORN OFF relay 44WF (the ground crew horn 15WC comes on),
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the relay 39WF also energizes the APU FIRE light 40WF on the external power panel 108VU (the red APU FIRE light 40WF comes on).
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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),
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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. 28-29-00) (the APU low-pressure fuel-shutoff-valve 14QM closes),
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the relay 5WF also sends a signal to the APU Electronic Control Box (ECB) 59KD (Ref. 49-62-00) (the ECB 59KD starts the APU emergency shutdown sequence),
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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).
C. APU Fire-Extinguisher Bottle-Overpressure If there is an overpressure (overtemperature) in the fire extinguisher bottle:
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the pressure relief device operates automatically,
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the extinguisher agent is released and flows through the overboard discharge pipe to the discharge indicator,
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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),
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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).
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