Originally Posted by
Jet Jockey A4
601/604/605 and 650 work the same way… if the APU was running it’s generator would be on standby and stay in that mode even with a dual engine failure.
The ADG should deploy automatically and provide limited electrical power but if you want the APU’s generator to take over and feed the electrical power, you need to select a switch that will change the power source.
Thanks for the clarification, it’s been a minute since I’ve flown a challenger - and that was a 601 which if I recall had a limitation that the APU gen could not be used in flight unless both engine gens had failed - so even after we started the APU and transitioned the bleeds descending through 10 we left the APU gen switch off until after landing. That limitation may have been removed if the APU was upgraded to the -150.