What are APU and EPU?

• A. APU: emergency power source for flight controls; EPU: ground power generator.
• B. APU: small jet engine/generator for ground power. EPU: emergency source of electrical/engine/hydraulic power for flight controls.
• C. APU and EPU are onboard computers.
• D. APU is a water purification unit; EPU is an energy storage device.

Answer: (B)

APU means an on-board small jet engine that drives a generator to provide electrical power (and bleed air) when the engines are not running or during ground operations. It powers aircraft systems and can help start engines and run air conditioning while on the ground. EPU is a dedicated emergency power source that supplies electrical, hydraulic, and sometimes engine power to keep essential flight controls and systems functioning if the main power sources fail. This combination matches the description: the APU is a small jet engine/generator for ground power, and the EPU provides emergency electrical/hydraulic/engine power for flight controls. The other options mix up these roles or cite unrelated equipment.