- The SES provides power for emergency APU starting both in-flight and on theground. SES motors the APU via the turbine power motor to provide emergencyelectrical and hydraulic power. Once the APU is supplying emergency power to theaircraft, the SES automatically returns to a ready state. The SES also provides pneumaticenergy for alternate landing gear extension, arresting gear, and APU door operation. AnSES fuel bottle, in the aircraft left side of body, stores fuel for combustion by the turbinepower module during emergency operation and APU start. Air from two SES air bottles,in the aft fuselage, expands a bladder in the fuel bottle to pressurize it. A rechargeassembly has a hydraulically powered compressor to recharge the SES air supply bottleafter use. There is also a ground service connection.