Originally Posted by
FlyingStone
I don't know which aircraft are you flying, but me thinks if APU cannot be used in a cold-soaked state, it shouldn't be installed or certified.
What are you going to do if a generator or engine fails in cruise? Divert towards the equator, fly at 1000ft with APU inlet door open to "warm it up"?
KISS principle very much applies here.
1 tiny detail: APU does windmill a little with forward speed which is why we preferred to start them on short final. Makes a gigantic difference for flights longer than 2-3 hours. On the classic 737 that was. Had many failed starts on the apron, none on short final. And we had some APU fires at higher attitudes in the company, so they’re tricky to say the least.