(4)
Position DC METERS selector switch to BATTERY.
(5)
Position AC METERS selector switch to APU GEN.
(6)
Position BATTERY switch to ON.
(7)
Check that APU bleed valve switch is OFF.
(8)
Momentarily position either APU generator switch to ON to close field relay.
(9)
Position No. 1 tank forward fuel boost pump selector switch to ON.
NOTE: If ac electrical power is on the airplane, select No. 1 generator bus. The No. 1 tank boost pump will then assist the APU engine driven fuel pump during starting.
NOTE: If you must use the fuel boost pumps in the center tank, you must have a maintenance person or observer in the flight compartment to continuously monitor the LOW PRESSURE lights. Turn the applicable fuel boost pump to the OFF position if the LOW PRESSURE light for the center tank stays on.
C. Start APU
CAUTION: AN UNDETECTED FIRE COULD OCCUR IN THE APU COMPARTMENT WITH THE APU COWL DOOR OPEN AND THE LOWER SHROUD REMOVED. IF THIS HAPPENS, THE APU FIRE DETECTION SYSTEM MAY NOT SENSE A SMALL FIRE AND MOST OF THE FIRE EXTINGUISHING AGENT WILL BLOW OUT OF THE OPEN APU COWL DOOR. IF A FIRE DOES TAKE PLACE AND IS NOT QUICKLY EXTINGUISHED, DAMAGE TO THE APU AND THE AIRPLANE CAN OCCUR.
(1) Make sure that there is an observer located near the APU compartment to watch for fire if the APU cowl door is open and the lower shroud is removed during APU operation.
NOTE: The observer should be in voice contact with other personnel in order to provide a warning if a fire occurs. Airplane personnel can then do the APU shutdown procedure and other corrective actions (including the use of portable fire extinguishers).
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WARNING: DO NOT OPERATE THE APU WITH THE LOWER SHROUD REMOVED IF PERSONS ARE IN OR DIRECTLY BELOW THE APU COMPARTMENT. YOU MUST BE A MINIMUM OF 3 FEET AWAY FROM THE OUTER EDGE OF THE APU COMPARTMENT OPENING TO OPERATE THE APU WITH THE LOWER SHROUD REMOVED. AN APU TURBINE WHEEL SEPARATION DURING OPERATION CAN CAUSE INJURY TO PERSONS.
(2) APU's WITHOUT ALLIEDSIGNAL SB GTCP85-49-7096; If you must operate the APU with the lower shroud removed, make sure all persons are not in the hazard area (Fig. 201A).
NOTE: APU's with AlliedSignal SB GTCP85-49-7096 have an external shield around the turbine plenum and have no hazard area.
(3)
Position the APU MASTER SWITCH to START and release.
NOTE: If the APU MASTER SWITCH is positioned initially to ON and the air inlet door fully opens before the APU MASTER SWITCH is moved to START, CLOSE coil of start and stop relay K1 will not be energized and the APU will not start.
(4)
Monitor EGT indicator, ac frequency meter, low oil pressure light, and dc ammeter.
CAUTION: TO AVOID DAMAGING APU, OBSERVE ALL OPERATING LIMITS (FIG. 201).
(a)
Low oil pressure light shall come on.
(b)
The APU fuel valve and air inlet door will open, in that order, in approximately 17 seconds.
NOTE: The APU fuel valve is located on the LH wing rear spar. Verify that the valve is open by observing from the LH wheel well that the valve position indicator goes to OPEN.
(c)
After the air inlet door is fully open, the starter motor will be energized, indicated by a negative reading of the dc ammeter, and engine rotation commences. Light off should occur within 15 seconds, as indicated by EGT rise.
(d)
Low oil pressure light shall go off.
(e)
Engine should accelerate to 100% service speed within the maximum time specified in Fig. 201. 100% service speed is indicated when the ac frequency meter stabilizes just over 400Hz only if the field relay is closed.
(f)
If a satisfactory initial ground-start of the APU does not occur, any subsequent APU ground-start requires a qualified ground-observer. The qualified ground-observer must make sure that the airplane surfaces are not damaged by a fire from the APU exhaust. If the flames from an APU exhaust fire are blown onto the airplane surfaces, all damaged areas must be examined.
(g)
If the engine does not accelerate to 100% service speed within 90 seconds, the APU will automatically shut down through the 90-second time delay relay of the starting circuit. Position the APU MASTER SWITCH to OFF, observe the starter duty cycle, then repeat steps C.(3) thru C.(4)(g). If the engine does not accelerate to 100% service speed on second attempt, maintenance action is required.
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