During engine start after 45% N1, which FADEC power source powers the channel?

During engine start after 45% N1, which FADEC power source powers the channel?

• A. EMER bus
• B. PMA
• C. Battery
• D. APU

Answer: (B)

During engine start the FADEC needs a stable, engine-driven power source to accurately control fuel schedules and timing. The Power Management Assembly (PMA), which is driven by the engine accessory gearbox, provides this primary power to the FADEC channels. Once the engine reaches about 45% N1, the PMA can reliably sustain FADEC operation, so the channel is powered by PMA. The emergency bus is reserved for emergencies and would only take over if normal power sources fail. The battery is a backup for ignition and limited systems when other sources aren’t available, not the normal FADEC power source after that start threshold. The APU can supply electrical power to the aircraft if it’s running, but for this scenario the engine-driven PMA is the intended FADEC power source.

During engine start the FADEC needs a stable, engine-driven power source to accurately control fuel schedules and timing. The Power Management Assembly (PMA), which is driven by the engine accessory gearbox, provides this primary power to the FADEC channels. Once the engine reaches about 45% N1, the PMA can reliably sustain FADEC operation, so the channel is powered by PMA. The emergency bus is reserved for emergencies and would only take over if normal power sources fail. The battery is a backup for ignition and limited systems when other sources aren’t available, not the normal FADEC power source after that start threshold. The APU can supply electrical power to the aircraft if it’s running, but for this scenario the engine-driven PMA is the intended FADEC power source.