TM 1-1520-240-102-12-1SECTION XII. AUXILIARY POWER UNIT2-12-1. General.The gas turbine auxiliary power unit T62-T-2B (APU) (fig.2-12-2) is mounted in the aft cabin above the ramp. Thebasic components of the APU are the gas turbine engine,hydraulic motor-pump, fuel control, accessory drive, andAC generator. An APU Electronic Sequencing Unit(ESU) which monitors APU operation is on the left sideof the cabin above the ramp. the ESU is also labeled APUCONTROL BOX.The motor-pump on the APU pressurizes the utility andhydraulic system for main engine starting and groundchecks. The APU also drives an AC generator whichsupplies power to the No. 1 and No. 2 electrical systems.Refer to Section VI for further information on the hydrau-lic systems. The APU oil supply is intergal and containedwithin the sump of the accessory drive assembly. TheAPU receives fuel from the left main fuel tank through abooster pump, a manual fuel shutoff valve, and a sole-noid valve.2-12-2. Electronic Sequencing Unit.The ESU is mounted on the left side of the cabin abovethe ramp. The unit monitors APU starting and operation.in addition, it monitors APU speed and exhaust gas tem-perature. the unit continuously compares these parame-ters with limits programmed into ESU circuits. If a limit isexceeded, the ESU will automatically shut down theAPU.NOTEThe BITE indicators indicate engine conditiononly. They will not indicate a defective hydrau-lic motor-pump or generator.Four magnetic built-in-test-equipment (BITE) indicatorsare on the ESU. These indicators are either black orwhite. A label on the ESU explains the various BITEindications and their meaning.2-12-3. APU Switch.The APU switch is on the ELEC panel of the overheadswitch panel (fig. 2-11-2). It is a three-position switchlabeled OFF, RUN, and START. The switch is springloaded from START to RUN. Normally, power to operatethe APU is supplied by the DC essential bus through theAPU CONT NORM circuit breaker on the No. 1 PDP.Emergency power to operate the APU is from the batterybus through the APU CONT EMERG circuit breaker onthe No. 1 PDP.2-12-4. APU ON Caution.The APU ON caution capsule is on the mater cautionpanel (fig. 2-14-5 and 2-14-6). Normally, the APU is in-tended for ground operation only. It is not intended foroperation during flight. If the caution remains illuminatedfollowing take-off, it alerts the pilot to shut down the APU.When the caution is illuminated it indicates the APU is upto speed and the exhaust gas temperature is normal. Itdoes not necessarily indicate that APU hydraulic pumpor generator output is normal. If rotors are not turning,check the UTIL HYD SYS and RECT OFF cautions toevaluate output of the APU hydraulic pump and genera-tor. The APU ON caution is controlled by the ESU.2-12-5. Emergency APU Fluid Shut Off Vavle.The EMERGENCY APU FLUID SHUT OFF VALVE is inthe fuel supply line to the APU (fig. 2-12-1). It is locatedinside the aft cabin above and to the left of the rampinterphone station. The valve can also be reached fromthe outside through an access door labeled ACCESSAPU EMER FLUID SHUT OFF. The knob on the valvehas an OPEN and CLOSE position. Placing the knob toCLOSE shuts off fuel to the APU.Figure 2-12-1. Emergency APU Fluid Shut OFFValve
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