CAUTION: TO AVOID DAMAGING APU, OBSERVE ALL OPERATING LIMITS (FIG. 201).
NOTE: If the APU MASTER SWITCH is turned OFF before 100% speed is reached, the overspeed light may come on. This is a normal condition and is caused by an electrical signal input to the overspeed oscillator of the electronic speed switch. The overspeed light will extinguish following a normal restart of the APU.
(h) The APU GEN OFF BUS light should come on at 95% speed to indicate that the unit is ready to receive load.
NOTE: Operate the APU in a unloaded condition for a minimum of 1 minute prior to application of a load to allow temperature to stabilize.
D. Shut Down APU
(1) Normal Shutdown
(a)
Disconnect all load except APU generator supplying No. 1 generator system (bus transfer switch OFF and No. 1 tank forward fuel boost pump ON). Allow the engine to operate at this condition for 1 minute.
NOTE: With ac electrical power available, shut down the APU with power on the No. 1 generator system and the No. 1 tank forward fuel boost pump ON.
(b)
Position the APU MASTER SWITCH to OFF. APU fuel valve and air inlet door should close in approximately 20 seconds after shutdown initiation.
(c)
Check that the cooling air shutoff valve is fully closed (actuator rod is retracted when valve is closed).
(d)
Position the BATTERY SWITCH to OFF.
(e)
Position No. 1 tank forward boost pump switch to OFF.
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(2)
Shutdown Using Fire Switch
(a)
Pull either fire switch.
NOTE: When either fire switch is used for APU shutdown, fire extinguisher discharge button is armed in addition to APU normal shutdown functions. A check of actual presence of fire should be made, if possible, before discharging the fire extinguisher bottle.
(b)
Position MASTER SWITCH to OFF.
(c)
Position No. 1 tank forward boost pump switch to OFF.
(d)
Reset fire switch.
(3)
Automatic Shutdown
(a)
After automatic shutdown occurs, determine cause for shutdown, then position MASTER SWITCH and No. 1 tank forward boost pump switch to OFF.
(b)
On airplanes with electronic speed switch with starter overspeed protection, if an automatic shutdown occurs approximately 11 to 15 seconds following starter engagement, check that tachometer-generator is functioning as required.
(c)
Correct malfunction, and restart per par. 2.C.
3. Motor APU
A. General
(1)
Engine motoring is generally required for depreservation of a new engine and to purge air from the fuel lines after replacing fuel system components or checking low pressure fuel filter. However, motoring of an engine may be performed for testing engine components.
(2)
If motoring run is to be performed for maintenance other than fuel system purging or depreservation of engine, disconnect electrical plug from sequencing oil pressure switch.
(3)
Fuel tank No. 1 must contain a specific amount of fuel for APU operation (Fig. 201). The APU fuel inlet line must be filled with fuel before attempting to start the APU. The fuel inlet line is filled and pressurized using the No. 1 tank forward boost pump. To turn on the No. 1 tank boost pump external ac power is required.
B. Equipment and Materials
NOTE: Following equipment is required for fuel system purging and engine depreservation.
(1)
Container - 2 gallon minimum capacity
(2)
Fuel hose
NOTE: Fabricate fuel hose to reach container and to mate with the fitting on end of high pressure fuel line disconnected from fuel atomizer.
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C. Prepare for Engine Motoring
(1)
Position BATTERY SWITCH to OFF and placard.
(2)
Open APU compartment access door latches and open door. Install door support rods.
(3)
Support shroud, open shroud latches, and remove shroud.
CAUTION: EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
(4)
Disconnect electrical plug from sequencing oil pressure switch.
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