(2)
 APU Starting During APU start the IGVs are closed to reduce the load on the compressor.

 (a)
 In Flight Operation During flight operation, the opening or closing of the IGVs depends on the system demands. If the EGT exceeds the limits the IGVs automatically move towards the closed position to reduce the load on the compressor. IGV control failure will automatically move the IGVs to the closed position.

 (b)
 The relationship between % actuator position and guide vane angle is as below where 100% means fully open:

 Actuator Position %  IGV Angle (degrees)
 00.0  82
 22.9  60
 43.7  40
 64.6  20
 85.4  00
 95.8  -10
 100.0  -14
 D. Surge Control
 (Ref. Fig. 004)

 The ECB 59KD controls the Bleed Control Valve (BCV) (8051KM) to prevent surge of the APU load compressor. The valve is of the butterfly type and has a compressed air inlet and two exits, one to exhaust,the other to the aircraft system. The flap diverts the air to the aircraft system when open and exhaust when closed. The ECB receives electrical signals from sensors through transducers from delta P and static pressure (Ps) at the discharge of the load compressor. The pressure sensors are assembled as one unit and are mounted on the air inlet plenum. Should delta P and static pressure fall below a defined value, the bleed control valve will start to close to prevent surge. If surge or reverse flow occurs, the ECB will command the bleed valve to close. If the surge continues and the BCV cannot be closed, the ECB will initiate APU shutdown. Failure of the transducers or the analog/digital converters will cause the ECB to close the valve and allow the compressed air to discharge to exhaust.
 E. De-Oil Logic De-oiling is done independent of the oil temperature at each shutdown commencing at 90% speed. When both speed sensors (8060KM1) and (8060KM2) have failed, the de-oil valve is energised 2 seconds after the fuel solenoid is de-energised. De-oiling is performed at each start commencing 1.5 seconds after the back-up start contactor is energised until 55% speed is reached.

 Load Compressor - Surge Control
 Figure 004

 CES  F. Protective Shutdowns

 (1) An APU shutdown may be due to the following conditions.
 (a)
 Overspeed An overspeed shutdown occurs when the speed is more than 105%. The speed is detected by two electromagnetic sensors located on the reduction gearbox casing and in front of a common target gear. To provide full redundancy for overspeed protection, one phase of the PMG is used to check the speed. When the speed reaches more than 107% the fuel solenoid is de-energised. In case of detection of a speed injection test failure, both primary channels or watchdog circuit failure, a restart will not be possible for safety reasons.

 (b)
 Overtemperature Overtemperature shutdown occurs when EGT exceeds the following limits.

 DURING STARTING PHASE
 TEMP LIMIT
 SPEED  TEMP LIMIT  (above 25000 ft.)
 0  426 deg C  426 deg C
 10  788 deg C  788 deg C
 20  900 deg C  900 deg C
 30  900 deg C  900 deg C
 50  853 deg C  900 deg C
 60  --- deg C  900 deg C
 80  788 deg C  843 deg C
 100  670 deg C  760 deg C

 DURING STEADY STATE (APU available)
 T inlet (deg C) I EGTSD (deg C)
 -----------------------+--------------------------5 I 640 33 I 682
 EGT shutdown if EGT = EGTSD for 4.5 sec
 or
 EGT shutdown if EGT +60 deg C = EGTSD

 (c)
 Low Oil Pressure (LOP) APU shutdown occurs when the low oil pressure switch (8091KM) input to the ECB indicates LOP after the APU has reached 95 % speed.

 (d)
 High Oil Temperature (HOT) APU shutdown occurs when the RTD detects a gearbox temperature above 275 deg.F (134.99 deg.C) or a gearbox temperature failure in conjuntion with a generator oil temperature in excess of 320 deg.F (159.99 deg.C)

 (e)
 No Flame APU shutdown occurs when the EGT does not rise at least 100 deg.F

 (37.77 deg.C), 6 seconds after the APU reaches 5 % speed.

 (f)
 No Acceleration APU shutdown occurs if:

 -failure to crank, The APU speed fails to reach 3% within 2 seconds after main start contactor is energised. When the main start contactor is energised and starter motor voltage is less than 5.0VDC, the main and back-up contactor outputs do not indicate failed then, t delay = 12 seconds otherwise t delay = zero. For temperatures between 70 deg.F
　
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