The auxiliary power unit (APU) is a Honeywell 36-150BD constant-speed gas turbine. The APU is a self-contained unit with automatic fault detection, automatic and remote shutdown, and in the event of an APU fire on the ground, automatic fire extinguishing.

The purpose of the APU is to provide electrical power from a 400-amp DC generator and bleed air for the pneumatic system. Under high demand, the APU electrical loads take priority over pneumatic loads. The auxiliary power unit (APU) is installed in a fire-proof compartment in the tail-cone of the airplane. The APU compartment is accessed by a single panel aft of the aft equipment bay door.

The maximum operating altitude for the APU is 37,000 ft. APU generator operation is limited to 30,000 ft. Main engine starting and ECS operations are limited to 20,000 ft.

An engine control unit (ECU) controls and monitors all facets of APU operation, including the recording of operating hours and start cycles. The DC-powered ECU sends operating data to the EICAS displays. APU start is initiated by one switch on the APU control panel in the flight compartment. Operational control of the APU electric and bleed-air systems is performed at the ELECTRICAL and AIR COND/BLEED control panels. For ground operations, a remote cutoff switch is located on the right side of the aircraft, aft of the wing and behind the electrical connection access door.