I work at manchester airport and often witness aircraft coming onto stand unable to turn their engines off persumably as no ex pwr is connected, but why isnt the APU running pre coming on stand?
Prob APU is U/S.
also when ex pwr is connected, why isnt the APU turned off straight after? the flightdeck has now got an alternative pwr source, is this down to the crew not realising ex pwr is available?
Ground power connected does not mean that the aircraft will be air conditioned. Even on a moderate day of 15-20C will lead to much higher temps in the cabin. APU is operated to keep one or maybe two packs working in order to keep the cabin either cool or warm!
Also, during darkness, often APU is kept running until the last pax disembarks as ground power sources can be unreliable, the cabin going almost completely dark when they do fail!
Hope that helps.