NetJets Longitude Initial Systems Practice Test

Standby power is designed to keep you oriented when the main electrical system fails. The standby battery is sized to supply the standby instruments for about 180 minutes, or 3 hours. That three-hour window ensures you have enough time to recognize the failure, manage the airplane using the remaining systems, and complete a safe approach and landing. Shorter durations wouldn’t give enough time to divert and land safely, while a much longer duration would require a larger, heavier battery with little justification for this part of the standby system. So 180 minutes is the appropriate duration for keeping the standby instrument powered.