B777 Cabin Temp increase with packs off

[mutt]

We are starting to use PACKS OFF for takeoff due to a requirement for increased takeoff weight. Based on the procedure that PACKS will go OFF just before takeoff and be turned back on couple minutes later. Does anyone have any idea of the expected rise in cabin temperature, especially from hot airports.

Mutt

[Pontius]

Hi Mutt,

If it's anything like the 744 then it'll be insignificant. Maybe 1 deg down the back and probably stay the same at the front. That's with packs off just before take-off and start to put them on again once CLB thrust is annunciated at 1000'.

[ACMS]

it's only 1 to 2 deg C if you do it just before T/O even on a 35c day. Do it any sooner with a full ship and it will get warm quite quickly.

[Old Smokey]

As said by the others Mutt, it's no big deal. Temperature rise even in Middle East type temperatures is hardly noticeable, the only thing that gets occasional passenger comment is the reduction in air flow, but the Recirc Fans help to relieve this.

The one factor guaranteed to cause some discomfort is if the over-enthusiastic PNF closes both Packs at once after Takeoff, giving a pressure bump. One at a time is barely noticeable.

Regards,

Old Smokey

[mutt]

Thanks for the responses..... OS, just to cheer you up, this procedure will be introduced with improved climb, so no more balanced field, albeit only at one airport where a 14,000 kgs takeoff weight improvement is the result.

Cheers

Mutt

[Old Smokey]

Hi Mutt, at last you've gone unbalanced!!! I'm going to buy a lottery ticket, I have visions of my unbalanced friend, J_T smirking!:}

I've seen some very good weight increases with B777 Increased Speeds, but none of the magnitude of 14,000 Kg come to mind. If it doesn't compromise your anonymity, which Airport and Runway is that?

On the topic of Packs Off Takeoff, do you use the APU to Packs option on the -300ER? Nice, but for minimal discomfort Vs Packs Off (which gives the same performance result), always thought it a lot of extra expense for a small gain.

Regards,

Old Smokey

[KRUGERFLAP]

Nobody can say a precise time . Depends on humidity outside temperature ,elevation,because an aircraft is not that well sealed.
A lot a factors. But whatever,it´s only a few minutes.

It´s a good question for the QR Command Interview,LOL.

[Spooky 2]

I read a report recently regarding a BA767-300 doing a packs off takeoff down in Entebbe. They briefed the FA's that the doors might rattle a little do to the lack of a positive pressure on the seals. None the less they did get a door warning light on the T.O. roll and rejected the takeoff with a resultant deflation of the tires. Very interesting as frankly I would not have thought of that possibility and I have done numerous packs off takeoffs in both the 767/777 and the MD11. You learn something new in this business everyday!

[Mt-Fuji Turb]

I am not quite driving those types of a/c yet but just for my understanding of PACKS...is this some sort of heat exchanger that regulates air temperature from the engine bleed air?
just wanting to learn

Cheers folks

[Old Smokey]

Welcome to PPRuNe Mt-Fuji Turb,

The answer to your question is YES. You could do a Google on "Packs", if this fails, try "Air Conditioning Packs".

Regards,

Old Smokey

[aidey_f]

"They briefed the FA's that the doors might rattle a little do to the lack of a positive pressure on the seals"

Now there's a thought: from the dark recesses of my aircarft design lectures, I have a recollection that pressurisation the fuselage during the takeoff run is one of the assumptions for the fatigue spectrum generation for the fueslage structure design. Something to do with the effect of the pressurisation reducing the compression loads in the lower half.

If we're all going to start delaying the pressurisation sequence until you're in flight, it might be an interesting project to see if there are any implications. I suspect not, but I wonder if anyone's done the maths?

[eightyknots]

A packs off take off is quite noticable down the back, it sounds and feels quite different from the norm.

It's always a good idea to tell the cabin crew if you're going to do one, just so that they don't phone you during the take off because they think something is wrong.:ok:

[bvcu]

Only problem is it wrecks ACM's . Think about it, packs on ground for a couple of hours, all machinery nice and hot . switch off for 5 mins , ACM fills with water , major corrosion issue and very high failure rate. Note we were doing it every time due company procedures until Boeing pointed out that nobody else was getting the failures . But to put it into context if you're only doing occasionally for perf reasons shouldnt be an issue .

[indiscipline_girl]

where a 14,000 kgs takeoff weight improvement is the result.



I certainly doubt this figure. I think you probably meant 1,400 kgs.

I ran a few numbers and the best improvement on the 744 was around 4,000 kgs. All numbers on the 777-300ER were within 1-2000 kgs.

[mutt]

I certainly doubt this figure. I think you probably meant 1,400 kgs.

Welcome to the Pprune Tech Forum...... thanks for your advice, but if i meant 1,400 kgs, i would have said 1,400 kgs! You cannot give an answer like yours without knowing:

1: Aircraft / Engine configuration
2: Airport
3: Temperature
4: PEP version
5: Previous operational procedures

So please be very careful about about sweeping statements about doubting figures!

Mutt

[indiscipline_girl]

Please enlighten as to 1 through 5 above to attain 14T improvement.

I honestly would like to know.

[mutt]

FAA Approved Airplane Flight Manual
BOEING AFM-DPI Performance Software
Critical Takeoff Limit Weight Report


Case 1
Air Cond Bleed = On
V1 Selection = Balanced
Improved Climb = None

Takeoff Limit Weight
CRITICAL: Climb Limit 270043 KG

Case 2
Air Cond Bleed = Off
V1 Selection = Optimum
Improved Climb = Optimum

Takeoff Limit Weights
CRITICAL: Brake Energy Limit 284454 KG
CRITICAL: Climb Limit 284454 KG

284454 - 270043 =14,411 kgs

Sorry, but you gotta trust the AFM :)

Mutt

[indiscipline_girl]

OK. Seems I am missing something here. Here are some figures from our operational database. B777-300ER.

40C.QNH 990. NIL WIND. DRY. RTOW:-

PACKS ON PACKS OFF
LHR 27L 329.0 331.7
JNB 03L 267.8 270.9
DXB 12R 336.5 340.2
HKG 25R 333.3 336.7
AMS 36C 316.3 319.0

Where are we going wrong?

Put me out of my misery.

[mutt]

B777-200

Your data doesnt include Improved Climb.

OS, just to cheer you up, this procedure will be introduced with improved climb, so no more balanced field, albeit only at one airport where a 14,000 kgs takeoff weight improvement is the result

Mutt

[Old Smokey]

Mutt, I sense a convert in the making:ok:

J_T, where the hell are you? History is being made:D

Regards,

Old Smokey

[indiscipline_girl]

Excuse my ignorance but what is 'Improved Climb'?

[john_tullamarine]

Thank God .. at last, Mutt is a convert to the theology of overspeed takeoffs ...

For ID,

improved climb = overspeed takeoff

is a simple tradeoff. Minimum speed schedule for takeoff is well below best climb performance speeds .. ergo .. if you have a bunch of spare runway (considering obstacle problems) often you can increase the speed schedule to achieve a better V2 climb performance. This may increase your RTOW, depending on what was limiting for the basic calculation. In general, it is well worth having a looksee to check what the situation is for a given set of circumstances.

Important to keep in mind that there are quite a few ticks in the boxes needed before you end up with the best weight calculation .. sometimes a bit of pushing and pulling with the calculations can yield significant benefits.

[ACMS]

Improved climb T/O helps our 777-300ER's a bit out of VHHH on a hot day.

At 351.5 ( MTOW ) the V2 is about 192 !! passing 100' the TAS is up to 210 kts already !!