APU off after both engines running

Hey IFC couldn’t find any answers regarding this:
I normally have APU running and then start my pushback. While doing this beacon light goes on and im starting N2. After pushback is finished I start N1 and begin my taxiing. Hope I’m doing this realistically?!
What do I do with APU? After both engines are running I can turn it off. That’s how it is described several times on the forum. But what about taxiing with only one engine? To preserve fuel. Should I wait to put it off until both engines are running?
Thx in advance.

turn off APU after engine start, turn on before engine shutdown


As far as I am aware, one engine running will be sufficient to keep the systems alive.


If I’m not mistaken, the standard procedure for using the APU is to use it until power is being supplied to the aircraft.

The same is true for arrival. Turn the APU on once you are approaching the gate. This will keep the systems alive when you shut down your engines. You can turn it off when you are ready to despawn.

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APU is there to provide electrical power and bleed air to start the engines. Once the engines are on, they provide the electrical power, so yeah, the APU can be turned off after startup.

Right, the question was do I need both engines to keep everything alive or is the energy provided by one engine enough…

Yep. Cool.

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If this is correct and approved…

One engine will be sufficient.

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Just one engine will keep the systems alive. Just have the master battery on, of course.

Sure, thanks.

In real life, if you’re doing one engine taxi, you would keep the APU running until after youve started your second engine. Both to relieve the electrical load on one generator but also for the bleed pressure for second engine start.


That’s what I’ve done until today. But answers differ :).
Any RL pilot here to confirm the right procedure?

Real pilot here

On the CRJ, our APU is on before we pushback. Once we’ve got Engine #2 on, we begin our taxi to the runway on a single engine with the APU on. (APU and Eng#2 powering the aircraft’s systems.) Once we’re nearing the runway, we start up Engine #1 with the APU still on. Once both engines have been started, only then do we shut down the APU.

The logic for this is because the APU is able to provide enough bleed air to the engine for starting as is. If we were to do what’s called a “cross bleed” start off of #2 to start #1, we would need to increase the power lever of Eng. #2 to create enough bleed air pressure (psi) to turn over the engine that you’re starting (#1). This causes extra and excessive noise as well as unnecessary jetblast that could injure ground personnel and/or damage surrounding aircraft and property.

Aircraft will vary though because they use different APUs. The 747 can start 2 engines at once whereas some of our narrow body type aircraft cannot and can only do one at a time. Some starting procedures may vary as well based on aircraft and company policy for fuel savings, so what I shared is based on our RL practice.

Hope this helps


Absolutely thx man. I’ll do as described in future. what I did intuitively already

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