How is continuity of power for flight instruments maintained during a loss of AC power?

How is continuity of power for flight instruments maintained during a loss of AC power?

• A. Through the standby power system and essential DC bus, which remain powered by TRUs or battery as needed.
• B. They rely on external power only.
• C. They shut down.
• D. Through the main AC bus only.

Answer: (A)

When the AC power fail happens, flight instruments stay powered because there is a dedicated standby power path that backs up the essential DC bus. Normally, transformer-rectifier units convert AC to DC to feed the essential DC bus, but if AC is lost, the standby power system takes over from its own battery to continue feeding that same essential DC bus (and the standby bus) so the critical instruments—like attitude, air data, and other primary flight instruments—remain powered. External power isn’t relied upon in this scenario, and the main AC bus isn’t the source for those instruments during a loss of AC. This standby, battery-backed arrangement provides the needed continuity for a safe continued flight and approach.

When the AC power fail happens, flight instruments stay powered because there is a dedicated standby power path that backs up the essential DC bus. Normally, transformer-rectifier units convert AC to DC to feed the essential DC bus, but if AC is lost, the standby power system takes over from its own battery to continue feeding that same essential DC bus (and the standby bus) so the critical instruments—like attitude, air data, and other primary flight instruments—remain powered. External power isn’t relied upon in this scenario, and the main AC bus isn’t the source for those instruments during a loss of AC. This standby, battery-backed arrangement provides the needed continuity for a safe continued flight and approach.