How do the aircraft's electrical systems typically receive power?

• A. Ground power unit
• B. Engine-driven generators and an auxiliary power unit, with battery backup
• C. Solar panels on the airframe
• D. Hydraulic systems provide power

Answer: (B)

Power for a commercial aircraft’s electrical system mainly comes from generators driven by the engines, with an auxiliary power unit (APU) providing power when the engines aren’t running or when extra capacity is needed. A battery backs up the system for starting and as a last-resort backup if generators aren’t available. On the ground, a ground power unit can supply power before start, but in flight the engine-driven generators and the APU are the primary sources. Solar panels on the airframe aren’t used to power the aircraft’s systems, and hydraulic systems don’t provide electrical power.