TM 55-1520-240-T15-1.2 OVERALL ELECTRICAL CABLING INTERCONNECTIONS OF APU SYSTEM COMPONENTS, "INTERFACED" TO MAIN ENGINE "STARTER" COMPONENTS (Continued)15-1.2A.OVERVIEW - OF APU INTERFACED TO MAIN ENGINE STARTERSThe APU Interfaced to the Main Engine Starters includes the activation of the following components andinterconnections as shown in paragraph 15-1.2.1. Hydraulic STARTERS on each engine2. Engine START valves3. Solenoid-operated pilot valves on the Utility System Pressure Control Modules4. Start switches and relays5. Caution lights6. Ignition LOCK switch7. Start Fuel Solenoid Valve8. APU Fuel Solenoid Valve9. APU Fuel Boost Pump10. APU Electronic Sequence Unit (ESU)11. APU FAULT RELAY12. APU Ignition Exciter13. APU T62-T-2B EngineB.BRIEF OPERATIONAL DESCRIPTION OF MAIN ENGINE START SYSTEMOn helicopters without 74, when the Main Engine START switch is moved to MOTOR, the STARTER ONcaution light comes "ON" and the Engine Start valve "OPENS". The START VALVE applies UTILITY SYS-TEM PRESSURE from the APU to the Main Engine starter, thus rotating the Engine Starter and Compres-sor.On helicopters with 74, when the main ENG START switch is set to 1 or 2, the engine start valve"OPENS". The START VALVE applies UTILITY SYSTEM PRESSURE from the APU to the Main Enginestarter, thus rotating the Engine Starter and Compressor.NOTEFor additional information, refer to task 15-5.5 - ENGINE Hydraulic Starting SystemOperational Check and tasks 4.4 - Engine Start and Ignition System (Without 74) or4.10- Engine Start and Ignition System (With 74).C. BRIEF OPERATIONAL DESCRIPTION OF APU SYSTEMThe Gas Turbine Auxiliary Power Unit T62-T-2B (APU) is mounted in the aft cabin above the ramp. Thebasic components of the APU are the gas turbine engine, hydraulic motor-pump, fuel control, accessorydrive, and ac generator. An APU control box, ESU, which monitors APU operation is on the left side of thecabin above the ramp. The motor-pump on the APU pressurizes the utility and flight control hydraulic sys-tems for main engine starting and ground checks. The APU also drives an ac generator which suppliespower to No. 1 and No. 2 electrical systems. The APU receives fuel from the left fuel system thru abooster pump, a manual fuel shutoff valve, and a solenoid valve.The APU control switch is on the electrical power panel on the overhead switch panel. It is a three-positionswitch marked APU OFF, RUN, and START. The switch is spring loaded from RUN to START. To start theAPU, the switch is moved from OFF to RUN for 3 to 5 seconds, then set to START for 2 seconds, thenreleased to RUN. APU start is then automatic and controlled by the control box. The APU ON caution lightwill come on in about 10 to 12 seconds.NOTEFor additional information, refer to task 15-1.5, APU Operational Check.END OF TASK15-12
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business