Which power source powers essential DC bus components after TRU failure?

Which power source powers essential DC bus components after TRU failure?

• A. Battery
• B. External power
• C. Generator
• D. APU

Answer: (A)

When essential DC bus components must stay powered after a TRU failure, the aircraft battery is the source that keeps them alive. The Transformer Rectifier Units normally convert AC from generators or the APU into DC to feed the DC buses. If a TRU fails, that DC feed is lost, so the emergency or standby power path uses the battery, which is connected directly to the essential DC bus through protective circuitry. This lets critical systems stay powered for a limited time, giving the crew the means to manage the situation and complete a safe procedure. External power, generators, or the APU can’t reliably sustain the essential DC bus without functional TRUs, so the battery is the designed fallback for this fault condition.

When essential DC bus components must stay powered after a TRU failure, the aircraft battery is the source that keeps them alive. The Transformer Rectifier Units normally convert AC from generators or the APU into DC to feed the DC buses. If a TRU fails, that DC feed is lost, so the emergency or standby power path uses the battery, which is connected directly to the essential DC bus through protective circuitry. This lets critical systems stay powered for a limited time, giving the crew the means to manage the situation and complete a safe procedure. External power, generators, or the APU can’t reliably sustain the essential DC bus without functional TRUs, so the battery is the designed fallback for this fault condition.