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Packs after APU is started (cold weather)

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I'm trying to understand how this process is handled in real life:


1. I run before start checklist to the line

2. I start APU and set it on the bus

3. I ask ground crew to disconnect Air Conditioning cart (and GPU offcourse)

4. APU bleed air goes on


At this point I would normally run before start checklist below the line and ask for pushback. As I'm using GSX, in cold weather I do get information that due to cold weather engines should be started after pusback is completed and brakes set.


Issue: between the time when AC cart is disconnected and engines are on, Cabin gets really cold. Can I avoid this by setting packs to ON when on APU Bleed air and switch them off after pushback is completed and before I start the engines, so I don't run engine start on packs ON? This is what I'm actually doing and cabin gets warm enough to not get cool again when I turn packs off and start engines, but wanted to make sure if that's something that would happen IRL?

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We usually have the APU running ~mins before push and the pack(s) will come on after the 1 minute warm up of the APU.


We also start #2 first and after #2 is running, we close the ISOL VALVE and turn on the right pack.


If you've gotten the plane warmed up and loaded with packs, it'll hold an okay temperature for a while. Long enough to de-ice, at any rate.

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Understood. I guess I will just start the APU a bit earlier and let it warm the aircraft. As for isolating a pack goes, I thought it's only used in high temps to increase pax comfort but after some thinking it can warm up the aircraft so it really makes sense to isolate it when temperature is below 5 degrees.



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