(c)
Emergency Shutdown The ECB receives three emergency signals on the EMER SIGNAL input via the:
-
APU FIRE PUSH P/BSW on the ENG/APU FIRE cockpit panel,
-
APU SHUT OFF P/B
-
APU fire and overheat detection system (only on ground). The ECB will command the APU to shutdown if any of these emergency signal is active.
(d)
Overtemperature Shutdown The ECB has two overtemperature shutdown logics:
-
an overtemperature during the APU start sequence,
-
an overtemperature with the APU on-speed.
1_ Software Overspeed Shutdown
The ECB software compares the APU speed with the programmed
overspeed limit of 109 % rpm. If APU speed is more than 109 %
rpm for 20 ms, the ECB commands an APU shutdown.
2_ Hardware Overspeed Shutdown
The ECB has two separate hardware overspeed shutdown circuits.
Each of these circuits uses a different speed sensor input to
shutdown the APU. The overspeed limit is 107 % rpm.
The hardware circuits are tested at every normal (commanded)
shutdown of the APU. If both hardware circuits are declared as
faulty, the ECB will disable itself (see ECB shutdown).
1 Overtemperature Shutdown during APU start
_ The ECB calculates a limit for the EGT (T5). If the measured T5 is higher than the calculated EGT limit for more than 1 seconds, the ECB commands an APU shutdown.
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2_ Overtemperature Shutdown with APU on-speed
The on-speed overtemperature shutdown is controlled by an
on-speed T5 limit. The on-speed T5 is calculation is based on
the APU inlet temperature (T2) and the APU inlet pressure
(P2). If the actual T5 is higher than the calculated T5 limit,
the ECB will initiate an APU shutdown after a 1 second delay,
or during flight or MES mode after 1 to 4 seconds delay.
(e)
Not Applicable
(f)
Loss of Speed Shutdown If both speed measurement channels fail while the APU operates, the ECB commands an APU shutdown. A failure in the measurement channel could be caused by either the speed sensor or its associated ECB conditioning circuit. A failure of one channel does not cause a shutdown.
(g)
Sensor Fail Shutdown
1 Loss of EGT
_ The ECB shuts down the APU during APU starting phase when both thermocouples or both theromcouple measurement channels are declared as faulty.
2 Low Oil Level and Low Oil Pressure (LOP) switch failure
_ In case of a low-oil level condition and a failed LOP switch the ECB commands an APU shutdown.
(h)
Low Oil Pressure Shutdown An LOP input causes a shutdown, after a time delay, when the speed is greater than 95%, or when cooldown is active and the speed is greater than 60%. The time delay is 15.5 seconds if the APU oil temperature is less than 25F or if the aircraft is on the air. The time delay shall be 0.1 second if the aircraft is on the ground and the APU oil temperature is greater than 25F.
(i)
No Flame Shutdown An APU shutdown is initiated if the EGT is less than 400 +/-40F and the speed is greater than 7% for 14 +/-1 seconds.
(j)
Flap Not Open Shutdown The APU is shutdown if the ECB does not receive the INLET DOOR FULLY OPEN signal within 30 seconds after the APU MASTER SW is set to ON. Additionally the ECB shuts down the APU whenever the APU speed is more than 7 % rpm and the INLET DOOR FULLY OPEN signal is lost for more than 0.5 seconds.
(k)
High Oil Temperature Shutdown A no acceleration shutdown occurs during initial acceleration or after the APU is on speed.
(l)
If the following conditions are met simultaneously during acceleration, the APU is shutdown on no acceleration:
-EGT is greater than 400 +/-40F
-
Speed is greater than 7 percent (latched until NOTRUN is true)
-
Speed is less than 95%
-Acceleration is less than 0.2 percent/second
-RUN/STOP switch is in the "RUN" position
(m)
If the following conditions occur simultaneously for 5 seconds and on-speed, no acceleration shutdown shall occur:
-EGT is greater than 400 +/-40f
-
Speed is greater than 7 percent
-
Speed is less than 95%, after having been greater than 95 percent
-Acceleration is less than 0.2 percent/second
(n)
Reverse Flow Shutdown A reverse flow shutdown occurs when speed is greater than 50 percent, LCIT is not failed, and one of two following sets of condition are met:
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