The autostart And The Inflight Engine Start

[AeroTech]

Hi,

I have some questions regarding the autostart and the inflight engine start.

-Can APU start automatically in case of autostart?

-In case of inflight engine flame-out (engine out of the envelope), will the pilot use the crossbleed, dive (to have more speed), or use the APU?

What is the benefit of the autostart since:
a-the protections of the autostart are removed in flight (hot start can cause damage..........)
b-the APU cannot not be used pneumatically at high altitude (the recent APUs up to 17,000 or 22,000 ft)
c-the crossbleed start can overpower the operating engine (let's say in twinjet at high altitude).

Thank you.
Best regards

[nugpot]

Hello Aerotech

I'll try my best to answer and then leave it for anybody else to add.

Can APU start automatically in case of autostart?
Don't know of any aircraft that has an automatic start on APU. You might be outside APU start envelope.

In case of inflight engine flame-out (engine out of the envelope), will the pilot use the crossbleed, dive (to have more speed), or use the APU?
On most aircraft there are certain envelopes for different types of starts.

On a twin with one engine running while in the air, you would probably go for crossbleed start. (On my a/c, CRJ, this is actually your only option)

With double engine failure, you can only do APU start below FL130, so above that you will try windmill start. You need 300KTS plus, so you need altitude to accelerate and maintain that speed. Once you have one engine running, you will do crossbleed start.

I might misunderstand your use of the word "autostart". You have continuous ignition, which just runs the igniters continuously. I don't know of an a/c where the engine restarts automatically.

You also have a crossbleed start altitude limit and the pilots will know it well. If you are at altitude, you have time at your disposal, so it is not important to get engine going immediately. (You will be losing cabin pressure, so you probably won't glide from FL330 to FL150, where APU can run aircon packs, at best glide speed - you can just as well use altitude for windmill start)

We practice double engine failure in sim every year, especially after Pinnacle CRJ accident.

The actions would be the following:

1. Continuous ignition on.
2. If engines continue to wind down - set up for glide until in windmill start envelope.
3. Start APU
4. When ready (and in envelope) - accelerate to 300+KTS and attempt windmill start on both engines.
5. If that fails, try again until at FL130 (you can also just glide and wait for FL130)
6. From FL 130 try APU starts until you run out of altitude or until you get one running.
7. Once you have one going, you can fly, so the rush is over. You then have time to try crossbleed for the other one.

For the knowledgeable - I have obviously left out all the other little actions in the checklists - this is more a sequence of events.

I hope this helps.

[Swedish Steve]

The B777 APU will start automatically in the air with loss of both engines. Can't remember the precis reason, but I do know that if you jack it up in the hangar the APU starts!

[SKYYACHT]

I believe that the APU auto start is actually initiated as a result of the loss of both AC busses. Naturally that would happen as a direct result of a double engine shutdown.

[AeroTech]

Hi,

Thank you for yours posts

Originally posted by nugpot
I might misunderstand your use of the word "autostart". You have continuous ignition, which just runs the igniters continuously. I don't know of an a/c where the engine restarts automatically


-According to a 744 crew (in another forum) the autostart can also perform and handle crossbleed start. If the restart is not successful, it will keep trying to start the engine. Is this valid for Boeing 777 or Airbus airplanes?

Originally posted by nugpot
You also have a crossbleed start altitude limit and the pilots will know it well if you are at altitude, you have time at your disposal, so it is not important to get engine going immediately. (You will be losing cabin pressure, so you probably won't glide from FL330 to FL150, where APU can run aircon packs, at best glide speed - you can just as well use altitude for windmill start)

-Do you mean that the crossbleeb start have altitude limit? (if the aircraft is out this limit, the crossbleed start can be performed?)

-Is there a cool down period of time for the starter after successive insuccessful crossbleed restarts? (or using APU bleed air at lower altitude)

Thank you. Feedback appreciated
Best regards.

[singleseater]

I can only reply re the 777 but a quick overview

As stated, the apu will autostart in the event loss of both AC Buses, but before that,
If an engine is sensed to be below the normal idle for the prevailing conditions, the the EEC,s will try to recover it, simply by starting the ignitors. As a result of this, RR/GE powered 777 do not have a selectable cont ign setting.(it may be an option for the GE,s)
If this intitial action is unsuccessful and the N2 goes below 35% then the engine is considered to have failed and displays as such.
All this happens without the involvement of the autostart.
Can result in a bit of confusion, can get an engine fail warning, but the engine is recovered, and operates normally.
Subsequently, the system will access the operating enviroment and indicate if a cross bleed start is advisable. This does not mean that a windmill start will not work, just that the best chance is with cross bleed. The system seams to prefer windmill starts if it can, prob because they are easier???
Once the start sequence has been manaully initiated, then the autostart will continue to try until it is told not to by manually turning the start off. This may be the airbourne autostarts you are talking about.
If both engines fail, then the sequence is basically the same, but with a lot more bells and warnings and higher pulse rates.