Cross Bleed to start other engine

[MackM2]

So I was just curious how to cross bleed to start an engine last night and figured it out. Really very simple, first get the hot engine rpm to at least 73%, select crank left or right engine depending on which you are trying to start. You will see the rpm creep up on the cold engine, it may stop at a low rpm so just bump up the throttle a little on the hot engine. At this point you will see the rpm on the cold engine climb up and once at 25%, move throttle detent on the cold engine and watch her fire up.

 

FYI: The Hornet will dump fuel on deck, found out the hard way when I hit the wrong switch in my pit.

[FZG_Immel]

so you mean with APU switched off already..?

[MackM2]

Yes, tried it after I landed and never touched the APU switch.

[erautour]

Try 80% on the running engine. That’s what is in the natops and has worked every time for me

[normanleto]

What is "crossbleed" word from? I mean what technical event happens when crossbleeding engines?

[Flamin_Squirrel]

What is "crossbleed" word from? I mean what technical event happens when crossbleeding engines?

 

Bleed air is compressed air used for (among other things) engine start, and is normally provided for starting by the APU. Cross bleed simply means air supplied across from one running engine to start the other.

[normanleto]

Thanks. Just reading Natops manual.

[CucoNegron6924]

Is there any particular advantage by using the crossbleed technique? Just curious!

[lefty1117]

So does this mean in a mid-air restart all you have to do is crank the other engine ??

[jamie_c]

Restart in flight I think requires 350kts airspeed, you windmill in flight instead of a cross bleed. Don't quote me on the numbers, 350 came to mind and I'm pretty sure it depends on altitude. Attempting it at slower speeds can cook the engine requiring replacement.

[MackM2]

@ Cuco: The only thing I’ve read on the net is airliners do it to save fuel during startup since you have the APU running along with a hot engine already up. Some argue the APU uses less fuel than using the hot engine to crossbleed. Think I may try to see the burn rate difference between the two processes, I was just curious more than anything about the topic. There may be some emergency type of reasons as well to crossbleed. Well...........in RL, maybe a compressor stall on left engine, then you had hit the APU and it doesn’t fire up! Then you have the crossbleed option.

[BarTzi]

IIRC NATOPS states you have to get special permission to use this on the carrier.

[Flamin_Squirrel]

@ Cuco: The only thing I’ve read on the net is airliners do it to save fuel during startup since you have the APU running along with a hot engine already up. Some argue the APU uses less fuel than using the hot engine to crossbleed. Think I may try to see the burn rate difference between the two processes, I was just curious more than anything about the topic. There may be some emergency type of reasons as well to crossbleed. Well...........in RL, maybe a compressor stall on left engine, then you had hit the APU and it doesn’t fire up! Then you have the crossbleed option.

 

Airliners won't routinely do this (and probably for the same reason BarTzi says NATOPS requires special permission) because the running engine needs to be run up, sometimes to quite high RPM, to start the other engine, which creates a hazard.

 

There are inflight restart envelopes for windmill, spooldown, crossbleed and APU. Some of these only overlap a little (or even not at all) so which one you go for depends on your circumstances.

[Stache]

Airliners do this when the APU is inop. Use a start cart ( high pressure air ) to start one engine, and then crossbleed start the other on a taxiway away from the gate. Only requires around 55-60% N1 ( technically you need 30 psi on the duct pressure gauge) on the operating engine, depending on field elevation.

Edited June 5, 2018 by Stache

[chief]

Yeah that’s the only reason why we ever do it. Either an APU is u/s or the apu bleed is u/s but something of the nature. On the 67 we need 60% n1 to crossbleed which isn’t much. If I remember correctly we needed a bit higher on the 37. Something like 70% n1.