Shutdown Packs=More power?

[rich49]

Hiya,
I understand the SOP on the 744 is to shutdown packs 1 and 3 on T/O to provide more power to the engines if the GTW is high. I was wondering, then, if on any aircraft you were to lose an engine, what would be the effect of shutting down the packs? Would this provide a little more power on the remaining engine?
Cheers

[Intruder]

The full procedure includes running pack 2 from the APU and closing the bleed isolation valves. That way, no bleed air is used from the engines to run the packs.

However, the procedure is not often required on the 744, especially with the GE CF6-80C2-B5F engines. There are few situations where an APU-to-pack 2 takeoff is required (VERY high temperature [>40C] and short runway [<9,000']).

The takeoff performance calculations include required climb performance on 3 engines in the takeoff configuration, so messing around with the pack switches at low altitude after an engine failure would be counterproductive.

[Flight Detent]

Hi all,
On the '74 Classics, ALL take-offs are 'packs off'!
That's whether it's a performance requirement or not, and normally the FE turns on the packs, one at a time, starting about 300' AGL.
That's except in the case of an engine failure, when he will be very busy anyway, unloading the pilots, so they can get on with flying the aeroplane, and he then turns on the first pack at the same time as the first flap retraction, the next when he feels the aeroplane is performing, and leaves it at that!

If it's really hot, as mentioned earlier, one or two packs are run from the APU until the flaps are up.

Great things, these FEs!!

Cheers...

[renard]

On the EMB145, we would ususally take of using a reduced thrust setting, and packs on.

If we have to use TO (MAX) thrust, for performance reasons, then we cannot use the engines to drive the packs.

If we take off in icing conditions, we have to have the packs off.

If we take off in non-icing conditions, then we can use the APU for driving the packs.

If an engine fails, we advance the thrust levers to max thrust, and the FADEC's reschedule for TO (take off) thrust.

Both of these actions will shut off the packs automatically.

[18-Wheeler]

On the '74 Classics, ALL take-offs are 'packs off'!


Unless it's =>44°C ambient, then it's one pack on for take-off.

[lomapaseo]

Just a musing, but on the large fan engines, I felt that the packs had less to do with total max thrust, than with the associated EGT margin.

Thus if you have lots of EGT margin (based on sea level hot day takeoff) than the engine limits the max thrust by burner pressure and rotor speed. If you open bleeds to power packs than your EGT goes up and may then become limiting to the engine before it achieves its maximum thrust capability.

Any other tech comments for or against this point?

[18-Wheeler]

I haven't really noticed the actual increase in EGT with the packs on, but I'd reckon it's a good 10°C or so. That's maybe 0.01 EPR's on a Roller at take-off power.

[Dragon Knight]

On some aircrafts the packs are shut down automatic if you were to lose an engine on takeoff.

[PifPaf]

rich 49 wrote:
Would this (shutting down packs) provide a little more power on the remaining engine?

The answer to your question is definetly yes. When you bleed your engine to power the pack, you are taking energy from it.
Just to give another example (besides that ones our friends already gave), when you have an engine failure on the 737-200, on the "1 eng inop ldg checklist" there's one step where you can configure your acft to become "APU bleed", in order to have extra power to an eventual go-around procedure.

Cheers,

PP

[rich49]

Thanks for your replies.

[Flight Detent]

Hey, my experienced friend, "18 Wheeler',
You're not thinking to well today, maybe you haven't flown for awhile, surely you remember doing the take-off performance card recently, where you added '0.02 EPR' to the t/o estimated EPR, because the packs were going to be off.

Was the Hajj good for you this year?

Have a good one,
Cheers

[18-Wheeler]

Page 4 of the "Flight Crew Brief", the one on how to do the performance data card & stuff.
The bottom paragraph says "An OAT greater than 44°C will require one PACK to be on during take-off."
See, I doread stuff! :)

FWIW, I looked at the EGT's today and saw the difference between none and three on was about 10°C EGT.

The Hajj is okay, I just got back from my last Jakarta trip. We'll be here for around a week or so longer fo Saudia. Can't wait to get home ...