(o)
Clogged Oil Filter Shutdown The ECB shuts down the APU after 5 seconds if:
-a clogged oil-filter signal is triggered and
-
the oil temperature is higher than 100 DEG.F (37.77 DEG.C) and
-
the APU is on governed speed condition (> 95 % rpm). This shutdown is inhibited during flight (TSO/JAR).
(p)
Start Period Timer (Slow Start) APU shutdown occurs when the Power Up Test (PUT) is complete, the start switch 2KA is operated and the air-intake flap is open and:
-
the speed is less than 7% after 30 s,
-
the speed is less than 20% after 50 s,
-
the speed is less than 50% after 70 s.
(q)
Main Power Interrupt Shutdown The ECB 59KD signals an APU shutdown if the DC input power is lost for more than 200 ms. The date and time of the loss of DC power is then stored in the ECB memory.
(r)
IGV Shutdown There are three conditions for an IGV shutdown:
1_ Two occurrences of LCIT increasing by more than 120F for 1.1
seconds where both occurrences are withing 7.5 seconds, but at
least 2.5 seconds apart.
2_ Two occurrences of LCIT greater than 350F for 0.1 seconds
where both occurences are with 7.5 seconds, but at least 2.5
seconds apart (there may be intermediate occurrences within
the 2.5 seconds). This condition will also be met if LCIT is
greater than 350F for 2.6 seconds.
1 The IGV command and position differ by more than 9.2 degrees
_ for 5 seconds when the speed is between 50 and 95%, or
2 The IGV position is above RTL and MES is commanded with the
_ position error greater than 9.2 degrees for 5 seconds, or
3 The speed is above 95% and the IGV position goes below RTL for
_
5 seconds.
R **ON A/C 063-099, 401-499,
(5)
Normal Shutdown Logic
(a)
Commanded Shutdown A normal APU shutdown is initiated when the operator pushes the APU MASTER SW from the ON to the OFF position. The ECB closes the IGVs to the min. position . The LCV closes and the SCV opens and the cool-down cycle of the APU starts.
(b)
Cool-down cycle The function of the cool-down timer is to delay the APU shutdown and to allow the APU to run for 60 seconds at a low stabilized temperature at 100% speed (N). The cool-down cycle starts immediately when the ECB receives the CLOSED signal of the LCV. The AVAIL signal remains active, the generator remains loaded if selected. If the LCV was not in the OPEN position during the entire APU operation the cool-down timer is set to zero (0) seconds. The APU enters the shutdown state immediately when commanded to shutdown.
If APU Bleed is set to OFF more than 60 seconds before the APU MATER SW is set to OFF the APU is shutdown immediately. If the APU MASTER SW is pushed before completion of the cool-down cycle the APU will shutdown only after the cooldown cycle is complete.
(c)
Overspeed Test After the end of the cool-down cycle, the ECB sends an overspeed test signal to the overspeed shutdown circuit. This causes the overspeed shutdown logic to start an APU shutdown by closing the fuel solenoid in the FCU. In this mode no protective shutdown is recorded by the ECB. After overspeed protection circuit is checked, the ECB attempts to modulate the fuel flow to keep the speed at 100 % rpm. If the ECB would be able to keep speed at 100 % rpm, it indicates that the fuel solenoid sticks in the open position.
(d)
APU Rolldown During APU rolldown the IGVs are set to the position corresponding to Bleed OFF until APU speed has dropped down to 80 % rpm. Then the IGVs are set to min. position. An APU re-start is possible at any time if the speed is more than 7 % rpm. When the speed has decreased to 7 % rpm the ECB commands the inlet door to close. Seconds after the speed is below 7 % rpm the ECB removes power from itself. The APU can be restarted at any time during the rolldown when the APU MASTER SW is set to ON and the START P/B is pushed. But the APU accelerates only when the APU speed has not fallen below 7% speed.
(6)
Protective Shutdown Logic The protective shutdown logic automatically shuts down the APU whenever continued operation of the APU would result in damage to the A/C, the APU or the ECB. The protective shutdown sequence is rapid:
-
The cool-down cycle is suppressed,
-
The ECB removes the power from the solenoids and torque motors
-
The APU fault light is energized,
-
The FAULT indication in the APU MASTER SW is energized,
-
The APU rolls down.
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