Originally Posted by
TangoAlphad
They are fairly quiet. When the APU comes on supplying the packs it gets fairly loud. An unofficial procedure is to turn left recirc fan off when running the APU + Packs as it is pretty noisy when briefing etc. Cuts the airflow noise down maybe 50%.
So if you dont have an air source during startup and only ground power, after putting the GRD PWR on the busses will you hear the recirc fans without the packs on and supplying air?