Approximately how long will the main batteries last with both generators offline?

• A. Approximately 33 minutes.
• B. Approximately 60 minutes.
• C. Approximately 15 minutes.
• D. Approximately 2 hours.

Answer: (A)

When both generators are offline, the airplane relies entirely on the main batteries to power the essential electrical buses. How long they last depends on how much energy is stored in the batteries and how much current the essential systems are drawing at that moment. The NGX training data uses about 33 minutes as the typical endurance under normal essential-load conditions. In other words, with the usual avionics, displays, autopilot, comms, and basic lights on, the batteries can sustain operation for roughly half an hour to half an hour and a half before depletion is reached. If you reduce loads (turn off nonessential equipment), you can stretch that time a bit; if you add loads, it will shorten the duration.