When to start and stop the APU 

It's primarily operator dependent, but the engines do need to be running a minimum of 3 minutes before takeoff for warmup and 3 min at idle after landing before shutdown. Ryanair afaik doesn't allow single engine taxi for takeoff. United does allow single engine for takeoff and landing.

Nice detail indeed! Now if only the engines did the same when you turn the packs on/off ;-)

@@A330Driver typical pilot mentality Emi; only perfection is almost good enough . . . !

Thanks for the insights! In theory we also have such an approach, in practical terms it prooved not to hold up however so the video was influenced more by what we actually do rather than what's in the SOPs. The "good mix" of what we actually do on the line. Especially when it's rather hot or rather cold (so most of the time... in winter one way, in summer the other) we need the air conditioning. So the APU comes on. The last thing you want is a cabin crew constantly nagging because they don't feel comfortable (and honestly... it's their workspace, why should I make them feel uncomfy only for the airline CEO to earn another two bucks?).

@@A330Driver That's interesting, I agree about the cabin crew, I would also like a comfortable temperature so I think it really is discretionary as you say but I also think there is a balance to try and meet the book also, that said I recently had a flight where the crew were flying by the book completely and left the Packs both off in Madrid - it was so hot and uncomfortable in the cabin until after takeoff, would have been nice to have cooled the cabin. I really like what you said about setting the cabin temps really far down before shutting off the APU to keep the cabin cool

Like the one took off LaGuardia AP and struck by birds.🤣

Are you allowed to say what airport you work at? That way we can simulate the same procedures there?

@@Sim737Pilot Somewhere in Norway. But i think its standard procedure in all of Norway. SAS, Norwegian, Widerøe. Its up to the airline. All of the charters we get start their APU on arrival.

That's a shame, bit of an old way of doing things.

@C H I have never seen it any airport, from JFK and ORD to the smallest outstation

@C H Commonplace here in EU. Saves noise and emissions...undeniably so!

In the papers it's usually noise, but emissions usually play a role as well of course. It all goes hand in hand. There's a huge difference between aircraft taking off and landing and APU usage however: Runways are usually much further away from terminals and resident houses. We can approximate that the percieved volume of something reduces linearly with distance. An aircraft with a running APU might therefore be percieved louder than an aircraft taking off on a runway that's a kilometer away. Also keep in mind that aircraft taking off and landing will only make noise for a short moment while the aircraft at the gate would do it for a long time.

@@A330Driver Interesting. It seems like APU regulations are way more common in Europe than North America. Like how trains in Germany never blow their horns unless there's a clear imminent danger but in the US it's horns for everything imaginable

Thanks William! In the 737NG according to Boeing it's one minute, according to my airline it's two minutes.

Yes, if the APU is not needed for cabin air conditioning (warm or cold). Ground power will obviously only provide power, not heating/cooling.

@@Sim737Pilot Thanks! 👍

At my airline in those temps the APU is running anytime crew or pax are on board.

He did say that even at +5*C, they can run it at own discretion to warm the cabin. I've done it myself, run the APU when we arrive for cold & dark power-on, warm the cabin just for 5 mins or so until it hits +15*C, then shut it down. During boarding, the passengers stir the temp up to +20*C, sometimes more. Then restart it again a couple minutes before push, unless we use external power. This was a large turboprop, so electrical starters rather than bleed air.