B-757 bleed off TO without APU

[izrailev]

Hello from Russia. Could You help me with next qwestion.
Am i allowed to take off with bleed off with APU unavailable? There is no such proceduren in OM. But our engines are going to exceed max EGT during TO. And can decrease power below 400 feet. Thanks.

[BOAC]

Certainly can in a 737 - it is in Supplementary Procedures. Not sure what you mean by the last sentence?

[izrailev]

So i meen can i decrease power below 400 feet in case EGT is going to reach the limit. And bleeds of TO is not supplementary procedure for 757.

[Mansfield]

The Boeing generic FCOM contains procedures for a PACKS OFF TAKEOFF and an APU TO PACK TAKEOFF. There is no procedure specifically for a bleeds off takeoff, although the APU TO PACK procedure states that it is "used for making a takeoff with no bleed air supplied from the engines".

The generic FCOM is not specific to a particular aircraft serial number, and there may be other procedures out there; but this is all I can find without access to your company's Boeing documents.

Would a packs off takeoff satisfy the requirements? This procedure makes no reference to an APU requirement.

[ajd1]

On the 757 the Packs Off take-off is effectively an unpressurised take-off. The procedure is to restore 1 pack after 1st thrust reduction and the 2nd when pressurisation stabilises.
The unpressurised take-off is no big deal, done it several times; as previously stated, the Boeing procedure makes no reference to the APU (in the Packs Off take-off)
Using the APU on take-off gives a performance penalty due to the intake door sticking out in the breeze, and APU to Pack take-off may not be used in Icing conditions.
As far as I know, there is no Bleeds Off procedure for take-off.

[izrailev]

Thanks a lot but I still don't have answer. I know about packs off TO, but I need exactly bleed off TO with APU inoperative. Is it legal or not? Reason that this procedure will decrease EGT much more then packs off.
And another qwestion: can i decrease power below 400' not to exceed EGT limit? With best regards.

[ajd1]

I can only talk about the 757 with RB211 535E4 engines. I have many thousands of hours on the type and have never seen the the EGT close to limits.
I say again, as far as I know there is no 757 procedure for a Bleeds Off take-off.
As for reducing thrust below 400', this would have performance implications .. the usual is 1000'agl or 1500'agl.

[Tree]

Packs off eliminates the bleed demand from the engines and should give you the same performance as bleeds off. Turning the bleeds off when the packs are off is redundant and will not achieve any performance improvement. There may be a miniscule amount of bleed used to pressurize the potable water tank but if so it will not be measureable.

[ajd1]

Exactly...

[Papa2Charlie]

I know this doesn't help much but it sounds as though the engines on the A/C are near the end of their life (i.e. time for an overhaul) if they're reaching EGT limits this frequently. Perhaps your airline could do a compressor wash to regain the EGT margin and therefore eliminate the problem of EGT exceedances with engine bleed on?

[muduckace]

I believe you may be confusing your aircraft supply bleeds with the bleed valves that open or close venting bleed air on a RB211 as it has no VSV's for power managment. The supply bleed valves being off have no effect on EGT limitation. The IP6, HP2 and HP3 valves perform this function.

[Storminnorm]

Does the MEL not have anything to say on the subject?
I would have thought that it is very undesirable to take
off without the cabin being pressurized to some degree?
Sounds as though the engines and APU need a good dose
of down time and sorting out the problems.

[Bluebird]

An inop APU should not have any impact on the EGT of the engines. Not during T/O or any other condition.

The 75´s usually have a 5- or 10 minute T/O thrust limit. By that time you should have passed 400', so if it is required to select climb thrust before that height, something is deeply wrong with the engines.

During normal operations APU is shut down prior to T/O, so again taking off should never be a problem on that aircraft with a APU inop. But if you have to select climb thrust before 400', then you have a problem.

Rgds-

[John Boeman]

Backtrack, surely you have come close though once or twice on the 767, maybe out of CUN?

[spacegrand]

Takeoff with one bleed off because it is u/s may be allowed subject to a number of restrictions. See your MEL.

You cannot accept an engine excedence except in an extreme emergency. You should reduce power so as not to exceed the EGT limit. You probably have a tired engine with a full power takeoff, a high surface temperature or a low level inversion.

It should only require a very small power reduction after selecting gear up to keep the engine in limits. Make a tech log entry, speak to your engineering dept and the chief pilot.