744 Packs off Take Off

[BN2A]

If a 744 can willingly haul itself off the ground in 30 degrees for a 14 hour sector, surely it can't be a performance requirement to do a packs off departure on a LHR - MIA on a chilly day??

Also a significantly less than full flap setting on landing with idle reverse.. Is that the norm these days??

Merely out of interest...

Anyone?

:)

[BelArgUSA]

Each airline has their procedures and policies.
Generally, takeoffs are flown packs OFF.
Flaps 10 or 20...
If you really want a pack, use the APU bleed with nº 2 pack.
Provided that your APU is not placarded "GND USE ONLY".
For landing, some airlines use flaps 25, some 30.
Auto brakes to minimum, idle reverse works fine.
xxx
I am a "Classic" 747 guy - but above applies to 744 as well.
:ok:
Happy contrails

[FCS Explorer]

RWY might have been contaminted. therefore u need more juice to accelerate faster to have more distance to stop in case of reject.

idle reverse is norm due to pax comfort and fuel saving
or probably they were planning for an exit further down the landing runway for operational considerations.

[c100driver]

There are other questions like who owns the engines, what is the contracted takeoff setting agreement with the owner of the engines, are you "power by the hour' or paying for overhaul, what thrust setting have you paid for etc?

There are many variables on how and why different operators fly and use different procedures as usual the devil is in the detail.

[mutt]

All got to do with fuel conservation which now governs every flying technique, packs off means greater thrust reduction and fuel savings. Less flap and idle reverse on landing means the same..... All of the KGS start to add up :)

Mutt

[barit1]

It all depends. Thrashing the engines to rated TO on a regular basis results in faster deterioration (EGT creep, SFC creep, less time on wing) which costs heavily in the spare parts dept. And although the book may show less trip fuel burn, you won't get as many trips out of the beast.

And if packs off gains you a few extra degrees EGT margin, that's money in the bank. :)

[parabellum]

Used to depart Singapore regularly to Europe on the B744, temp. 30+ and never used packs off once. It wasn't company policy out of Singapore. (Don't think I ever did do a packs off take off in ten years, from anywhere, but the memory isn't so sharp now!).

[the rim]

744 cannot use apu in the air so cannot use it to run pac's for take off ....look all the saving on fuel like shutting down engines on taxi only to spool up the remaining one,two or more so the aircraft can climb up the ramp to the stop mark...does it save any....i think not

[chestnut charlie]

744 can use APU in the air.APU to packs takeoff is available, APU is able to supply air to one pack up to 15,000ft. APU operates to 20,000ft but unable to supply any electrical power in flight.

[A Comfy Chair]

In 5 years (not a long time compared to some here!) I've only done a pack off takeoff once... longhaul out of JNB.

No other MTOW takeoff was performance limited with the packs on.

[Flightwatch]

Packs off T/O is a very useful tool at hot/high or short runways as it allows integrated T/O performance to be used giving up to 5T approx increase in MTOW depending on MACTOW. As an alternative APU to centre pack can be used to enhance pax comfort with a MTOW decrease of 100 kgs for the drag of the APU door being open.

Integrated take off performance has some limitations though such as dry runway etc. but is extremely useful on the 400F at places like NBO allowing a greater payload.

[TopBunk]

It is rare that a packs off departure is REQUIRED for performance on the 747-400.

In those circumstances, an APU to Pack 2 procedure is available to provide maximum payload, while providing air conditioning until engine bleed air is restored.

However, most departures from airfields below, say, 3000ft amsl, will see packs re-instated before the cabin climbs above 5000ft, which should be of no discomfort to the passengers.

In these circumstances, it saves engine wear and tear and thus promotes engine life and saves costs, to perform a 'bleeds off' take off. This allows take off at a lower thrust level, with reduced EGT's. As a consequence, it helps to keep down ticket costs!

For me, in my company, the flexibility to use an APU to pack take off has been removed, I see this as an ill-thought out procedure that fails to recognise the few stations (eg NBO, JNB, MEX) where it would be beneficial in the event of an engine failure for the expedience of a single procedure that saves a bit of fuel.

It should be an available procedure for use at the Captains discretion.

[Jofm5]

Sorry I am pure slf - and having been reading this thread with some interest. However, my problem is I cant seem to narrow down on the net what the pack (s) actually are. If one of you could please spare the time/give a brief explanation/enough info or direction as to where I can research what they are it would be much appreciated.

Back to lurking for me and happy flying :)

Regards

[collie77]

The packs basically provide air conditioning and are part of the air supply and pressurisation systems.

[Bullethead]

G'day Jofm5,

The 'packs' refered to are the airconditioning units usually called packs. The B747 has three of them situated in the belly of the aeroplane. They are aircycle machines and use bleed air from the engines for their operation thus draining some power from them.

Completing a 'packs off' takeoff allows the engines to develop full rated thrust which will give a performance benefit in a limiting situation such as at hot and high elevation airports or at high gross weights.

Sometimes the APU can be used to supply the bleed air and run a pack or packs for takeoff, in any case once the immediate performance requirements have been met normal pack operation is restored.

Regards,
BH.

[Dookie on Drums]

Furthermore,

PACK = Pneumatic Air Conditioning Kit.

[Jofm5]

Thank you for the explanations -in laymans terms for me I translate this to a car aircon, having it running impairs performance due to load.

I did find when researching the following on the boeing site (Boeing: Commercial Airplanes - Cabin Air Quality - Myths and Facts (http://www.boeing.com/commercial/cabinair/facts.html)) it says that turning one of the packs off saves little fuel as the other(s) compensate which if I understand correctly the fuel save option was removed on the 744 - I am guessing for the performance all packs must be switched off.

A very interesting and enlightening discussion, as slf - I normally consider we just roll and take off at max thrust and have not paid appreciation to the calculations you guys must make up front to make us do so safely. The more I read - the more I appreciate how complex your jobs are..

cheers

[mustafagander]

On the B744 check the MSN prior to packs off or APU to pack T/O. In my outfit some airframes do not have those options available.

[mutt]

This has nothing to do with the performance of the B744, and it appears to stem from an IATA Fuel Conservation initative that stated flex thrust takeoff, improved climb, idle reverse, packs off, low takeoff/land flap etc etc etc would save fuel....

It all adds up :)

Mutt

[SortieIII]

We are about to start doing packs off take-offs on the B744 as SOP. The reason being advanced by our technical boffins is 'environmental'?

[L337]

BA have a SOP that all takeoffs above 300 tons are packs off. It is not often a performance issue, more as has been alluded to, fuel and engine conservation. But they do operate hot and high where, on some days, packs off are required for performance.

eg. Jo'burg, Nairobi, Mexico.

And to muddy the waters, they also in addition load the aircraft with an aft C of G to squeeze the last kilo out of the performance.

[bcgallacher]

Packs off take offs will give a lower EGT for the same EPR or N1 setting - good for engine life.

[barit1]

Packs off take offs will give a lower EGT for the same EPR or N1 setting - good for engine life.

And since it's good for engine life, that equates to long-term fuel savings. :ok:

[wiggy]

And to add grist to the mill even an individual airline's SOP can change with time...in BA's case with the 744 from always having the packs on if performance allowed, then to APU to Ctr pack and then finally (perhaps) to all packs off above 300 tonnes...seems to depend on the latest enviromental priority /engineering demand / New Training Manager's previous fleet:bored:.....

[GlueBall]

Capt "mutt" . . . "All got to do with fuel conservation which now governs every flying technique, packs off means greater thrust reduction and fuel savings."

Actually, at some carriers it has more to do with pax comfort rather than rabid fuel conservation, sir. :ooh:

[Cartmen]

When selecting the packs back on after t/o we nearly always get a brief ">Trim Air Off" Eicas. It clears after about 5 secs.

Does anyone have a tip to stop this happening? ie. select Pack x on first?

[muduckace]

Actually, at some carriers it has more to do with pax comfort rather than rabid fuel conservation, sir.


Wow, I thought passenger comfort was an Idea abandoned back in the late 1980's. :ugh:

[stilton]

On an individual basis, flex / reduced power take off's do not save fuel.


Whilst not the most cost efficient profile when taking into account all other factors a full power take off followed by a max continuous thrust climb to altitude will save the most fuel.


This will allow the Aircraft to get to cruise Altitude as soon as possible where it burns the least fuel.


This is my technique when operating at the very limits of my Aircraft's performance on long range operations and has made a noticable difference.

[clivewatson]

What is the big deal - packs off or packs on? Just remember the three B's at 10K, bleeds (packs), babes and bulbs and all will be fine and dandy - especially with the bean counters.

[barit1]

stilton:
On an individual basis, flex / reduced power take off's do not save fuel.

Whilst not the most cost efficient profile when taking into account all other factors a full power take off followed by a max continuous thrust climb to altitude will save the most fuel.

You have stated this quite correctly, given your condition of min fuel for max range. I believe this is true for most turbofan aircraft.

Just don't overlook the " taking into account all other factors " for more mundane ops. Those "all other factors" are far from trivial.

[mutt]

Actually, at some carriers it has more to do with pax comfort rather than rabid fuel conservation, sir. Considering that this has bounced up again.... I would say that PACKS ON are for passenger comfort, PACKS OFF are for "rabid fuel conservation :)

Mutt

[CR2]

Hot-high-heavy = more payload.