What is the Power ON sequence for the electrical system?

• A. STBY Bus on first, 30 seconds for screens to power up, EPS On, Bat 1 and 2 On, External Power Last
• B. External Power, then Bat 1, Bat 2, EPS, STBY Bus
• C. Bat 1 and Bat 2 On first, then EPS, then STBY Bus
• D. EPS On first, then STBY Bus, then external power

Answer: (A)

Starting with the Standby Bus ensures there is a minimal set of critical instruments and references available as you begin the electrical system, so the pilot has a reliable cockpit reference from the moment you power up. Allowing about 30 seconds for the screens to power up gives the avionics time to initialize and stabilize, reducing the chance of inrush or reboot issues when the rest of the system comes online.

Turning on the Emergency Power System next provides a dedicated, stable power source for essential loads in case any main bus has a fault during start, safeguarding critical instruments and basic flight awareness. After that, energizing Bat 1 and Bat 2 brings up the main electrical backbone, enabling the rest of the avionics and systems to initialize with solid power.

Putting external power last prevents backfeeding into the external source and ensures internal sources are already stable before the aircraft connects to an external supply. This sequencing protects the electrical system and supports a reliable startup.