Besides starting the engines, what functions does the APU provide?

• A. Bleed air for the air conditioning packs and electrical power
• B. Hydraulic power for landing gear
• C. Primary propulsion
• D. Cabin lighting

Answer: (A)

The main thing being tested is what the APU does beyond starting the engines. An APU provides two key support functions: it supplies electrical power for the aircraft’s systems and it delivers bleed air to the environmental control system. That bleed air is used by the air conditioning packs to condition cabin air and support cabin pressurization, while the electrical power keeps systems running when the engines aren’t providing power. Hydraulics for the landing gear aren’t a standard APU function, and primary propulsion is handled by the engines themselves. Cabin lighting is part of the electrical system, but the distinct, primary APU roles are bleed air for the ECS and electrical power.