What supplies the required fluid pressure to the APU start motor and emergency hydraulic systems?

• A. Gas charge cylinder provides required fluid pressure to the APU start motor and emergency hydraulic systems.
• B. The APU start motor itself generates the hydraulic pressure.
• C. A hydraulic accumulator provides the pressure to the APU.
• D. A dedicated pump feeds the APU with hydraulic fluid.

Answer: (A)

The pressure for starting the APU and for the emergency hydraulic system is provided by a gas-charged hydraulic accumulator. A precharged gas cylinder (typically nitrogen) pushes on the hydraulic fluid, creating a ready-to-use pressure source. When you demand an APU start or need emergency hydraulics, that stored pressure drives the hydraulic flow to the APU start motor and to the emergency hydraulic actuators. The APU start motor itself doesn’t generate pressure; it uses the hydraulic pressure from this source to operate. This independent pressure source is crucial because it lets the APU start and emergency hydraulics function even if the main hydraulic pumps aren’t available.