Electrical power supply

The electrical synoptic shows which sources are available and which source is supplying each bus.

Initial power source

Connect ground power or start the APU as appropriate to the FSS procedure. For the AC GPU, AVAIL describes availability and IN USE indicates that it supplies the aircraft.

Bus supply

Open the electrical synoptic. Identify the bus being powered and any relevant source or contactor indications.

Observe transfer after engine start

Use the electrical synoptic to check which source supplies each bus after engine start.

Disconnect ground power correctly

FSS says to push the AC GPU button out before disconnecting the AC unit. Check the remaining power source and bus indications.

IDG disconnect

FSS describes DISC as a mechanical disconnect, separate from OFF. Use the normal procedure for routine source changes. ^[56]

The FSS AC page lists a source priority. Check the electrical synoptic for the actual source and use the checklist for source changes.