CES B. APU Normal Shutdown
(1)
When the MASTER SW pushbutton switch 14KD is set to the off position,
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if the bleed-air is not in operation, the ECB immediately starts the shutdown sequence.
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if the bleed-air is in operation, the ECB transmits a signal to close the bleed-air valve. When the pneumatic load is removed, the APU goes into a cool-down cycle. This shows on the Electronic Centralized Aircraft Monitoring (ECAM) system page as a decrease in EGT. After the cool-down cycle ends (up to 120 s) the shutdown sequence starts.
(2)
Shutdown Sequence
When the ECB starts the APU shutdown sequence:
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the AVAIL on the lower ECAM display unit disappears,
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the AVAIL legend in the START pushbutton switch goes off,
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the APU shuts down,
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the APU fuel LP valve actuator 3QF closes,
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the APU fuel-feed pump element 4QC and the control is de-energized,
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the air intake flap closes when the speed is less than 7%,
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the control and protection system de-energizes and resets when the speed is less than 7% and the air intake flap is closed.
C. Automatic Shutdown
(1)
The ECB 59KD keeps the shutdown information (faulty units and cause of the APU shutdown) in its memory.
(2)
An overspeed test signal of 109% is generated for 50 ms. If the overtemperature test is done, this test (overspeed) is delayed for
3.5 s The overspeed signal is put into the analog 'highest wins' logic and starts the APU shutdown (the APU fault signal is stopped). If after 20 s the speed is more than 85%, a shutdown circuit fault is recorded and all power is disconnected:
-
the AVAIL on the lower ECAM display unit disappears,
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the AVAIL legend in the START pushbutton switch goes off,
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the MASTER CAUT lights come on with a single chime,
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the upper ECAM display unit shows:
APU AUTO SHUT DOWN
MASTER SW ....................... OFF
-
the FAULT legend in the MASTER SW pushbutton switch comes on,
-
the APU shuts down without a time delay,
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the APU fuel LP valve actuator 3QF closes,
-
the APU fuel-feed pump element 4QC and the control is de-energized,
-
the air intake flap closes when the speed is less than 7%,
-
the control and protection system de-energizes and resets when the speed is less than 7% and the air intake flap is closed,
-when the MASTER SW is set to the off position, the FAULT legend goes off.
D. Environmental Control System (ECS) The ECS mode operates when the APU BLEED pushbutton switch is pushed and the air conditioning packs are in operation. Then the Zone Controller 8HK sends the ECS demand through the ARINC 429 bus to the ECB (Ref. 21-63-00). This sets the Inlet Guide Vanes (IGV) position in proportion to the ECS demand signal.
E. Main Engine Start (MES) The MES mode operates when the APU BLEED pushbutton switch is pushed and a main engine start is initiated (Ref. 73-25-00). Then the FADEC sends a signal to the ECB. This sets the IGV position in a fixed position in proportion to the inlet temperature and the T5 trim schedule. When the engine starter valve closes, the FADEC removes the MES signal to the ECB and the ECB switches back to the normal operation mode.
8. BITE Test
_________
A. BITE Test
The BITE tests the three subsequent BITE modes:
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the Power Up Test (PUT),
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the In Operation Test (IOT),
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the self test if started from the MCDU.
(1)
Power-Up Test (PUT)
The PUT starts if the subsequent signals are available:
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the power up initialization is complete and
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the APU speed is below 7 % or
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the start signal received for more than 60 seconds. During the PUT the drivers and the loads are tested for open and short. The switches are tested for thier position and the sensor signals are compared to thier limits.
(2)
In Operation Test (IOT) The IOT tests all LRUs which are necessary for the APU operation. The IOT starts after the PUT.
(3)
Self Test The self test is similar to the power-up test. It is opational when:
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the test is manual started from the MCDU,
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the APU speed is less than 7%.
(4)
Built In Test Equipment (BITE) For the indication of the report and test pages on the MCDU refer to the chapter 49-73-00 Analyzers.
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