Describe the typical preflight power-up sequence for a dual-generator aircraft.

• A. Connect external power if available, or use the battery to power essential loads; start engines to bring generators online, then switch to generators and verify bus voltages.
• B. Start engines first, then connect external power.
• C. Always use external power and never start engines.
• D. Power down all loads during start.

Answer: (A)

The essential idea is to keep critical aircraft systems powered during start and to bring the electrical system online in a controlled, safe order. On the ground, if external power is available, you connect it to supply the aircraft so the avionics and essential loads can be kept powered while you prepare for start. If external power isn’t available, the battery is used to feed essential loads so you can perform engine starts without losing critical systems. When you start the engines, the generators come online as the engines reach the proper speed and the generator control units engage, allowing the alternators to begin producing power. Once the generators are producing, you transfer the electrical load from external power or the battery to the generators and verify that bus voltages (and frequency, as applicable) are within limits and that both generators are supplying correctly. This sequence minimizes voltage dips during start, ensures essential systems stay powered, and confirms proper generation and bus health before flight.