VS744
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Airbus Air Conditioning During T/O

Sun Nov 11, 2007 10:09 am

I fly a lot on Virgin's A346 and have noticed on the last few flights that they turn the air conditioning off just before take off and it is not until you are well clear of the airfield that it comes back on (the process is very similar to what happens during engine start up). I've also noticed this on an alitalia A321, but not on the A319, 320 etc....

Does anyone know if this has always happened, or whether it was recently introduced and for what reason? I would take a guess at is being something to do with power but not sure whether it always happened or I only recently noticed it.

thanks!
 
FBU 4EVER!
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RE: Airbus Air Conditioning During T/O

Sun Nov 11, 2007 12:37 pm

We have started to this as a regular procedure on our (SAS) A330 and A340 recently. We shut off both AC packs before entering the runway and turn them on again after climb thrust has been set and with a minimum of ten seconds between each pack. We save some fuel and reduce maintenance costs on the engines. On some of our RR Trent engines with more than 2000 cycles, it is not recommended to shut off the packs at runway elevations higher than 600 feet.
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roseflyer
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RE: Airbus Air Conditioning During T/O

Sun Nov 11, 2007 1:51 pm

Shutting them off during takeoff can increase performance. It isn't a huge difference, but by decreasing the load on the engine from running the cabin systems, there is more power for takeoff. Each airline has its own set of criteria, but it doesn't have to be done.
If you have never designed an airplane part before, let the real designers do the work!
 
tom775257
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RE: Airbus Air Conditioning During T/O

Sun Nov 11, 2007 3:23 pm

Or just leave the APU and APU bleed on then you can leave both packs on.

On the A320 series if we take off packs off, our SOPs are 1 pack on at thrust reduction (1500'AAL) and then the second pack on at flaps zero. I've no idea about the A330/340.


Tom.
 
VS744
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RE: Airbus Air Conditioning During T/O

Sun Nov 11, 2007 6:11 pm

Interesting - I guess that explains some airlines doing it and some not, it must be an efficiency/power thing. i'll stop worrying about it now!
 
Airbus_A340
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RE: Airbus Air Conditioning During T/O

Sun Nov 11, 2007 6:44 pm

In Cathay we turn the packs off just before take-off, which fulfills our Before Take-Off Checklist. At thrust reduction PNF selects one pack on at a time, with a slight pause before turning the second one on.
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wilco737
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RE: Airbus Air Conditioning During T/O

Sun Nov 11, 2007 7:10 pm

The MD11F does switch off all 3 bleed air valves automatically when setting take off thrust... And switches it on again after passing 1500' AGL...
So you have all the air for the engines and dont waste it for the aircondition  Wink

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modesto2
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RE: Airbus Air Conditioning During T/O

Sun Nov 11, 2007 7:11 pm

At my airline, we run the packs off the APU until after takeoff. The "after takeoff" checklist calls for shutting down the APU and transferring the packs to the engine bleeds. However, our anti-icing systems on the E145 can only be run from engine bleeds, so for icing takeoffs, the packs are turned off so the packs can power the anti-icing system.
 
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HAWK21M
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RE: Airbus Air Conditioning During T/O

Mon Nov 12, 2007 3:29 am

Engine bleed extraction adds to the fuel burn to mantai desired EPR/RPM.
By using Bleed off T/O,this loss of Airflow/Thrust can be saved & utilised during the T/O.In todays world where Airlines are trying to save every smallest $,it makes sense.

Quoting WILCO737 (Reply 6):
The MD11F does switch off all 3 bleed air valves automatically when setting take off thrust... And switches it on again after passing 1500' AGL...

Is this a feature of every MD-11 or only the freighter.

regds
MEL
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wilco737
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RE: Airbus Air Conditioning During T/O

Mon Nov 12, 2007 8:07 am

Quoting HAWK21M (Reply 8):
Is this a feature of every MD-11 or only the freighter.

I guess for all MD11s, but I dont know because I only fly freighters...  Wink

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CoolGuy
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RE: Airbus Air Conditioning During T/O

Mon Nov 12, 2007 4:06 pm

How much power does an aircraft A/C use? And why would more power to the cabin affect takeoff thrust? It certainly makes sense but how does an engine power the electrical systems onboard?
 
tdscanuck
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RE: Airbus Air Conditioning During T/O

Tue Nov 13, 2007 4:43 am



Quoting CoolGuy (Reply 10):
How much power does an aircraft A/C use? And why would more power to the cabin affect takeoff thrust? It certainly makes sense but how does an engine power the electrical systems onboard?

A/C is a pretty significant power hog. I'm not sure how it works out on a pneumatic system, but the 787 A/C motors are in the range of tens of kW.

More power to the cabin affects takeoff thrust because it's power you're taking out of the engine. If you have a pneumatic tap, you're taking high pressure air from the engine which isn't available to be used for combustion (and hence provide thrust). If you have an electric system, the generator is driven by a driveshaft from one of the engine spools. Power out the driveshaft is power unavailable to spin the fan.

Tom.
 
pilotpip
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RE: Airbus Air Conditioning During T/O

Tue Nov 13, 2007 8:24 pm

We run the packs off the APU on takeoff and up to 10,000feet.

Unless we're taking off in icing conditions. The APU bleeds do not provide sufficient heat for the anti ice. As a result of the penalty of A/I, we turn the packs off on takeoff for icing takeoffs.
DMI
 
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HAWK21M
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 5:44 am



Quoting Pilotpip (Reply 12):
We run the packs off the APU on takeoff and up to 10,000feet.

What Type are you reffering too.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
wilco737
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 9:39 am

On the 737 we always had the packs on during take off! Runways were always long enough and the terrain no problem as well! Even with anti- ice on, there was still enough power left for the engines.
I only had to do one take off with PACKS OFF... It was in WAW, only the short runway was open, it was raining, runway pretty short and we were heavy. So we switched the packs off and took off! Anti- Ice wasnt needed...
And as I said on the MD11 ALL take offs are without the engine bleed! The engines have all the air they need  Wink It is an unpressurized take off! The APU is off as well. The outflow valve is fully closed so you don't feel much of the climb... and then the bleed turns back on and you get back your air  Wink

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HAWK21M
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 11:00 am



Quoting WILCO737 (Reply 14):
The outflow valve is fully closed

Why "fully closed".Is this a company SOP.
regds
MEL
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zeke
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 12:23 pm



Quoting Vs744 (Thread starter):
Does anyone know if this has always happened, or whether it was recently introduced and for what reason? I would take a guess at is being something to do with power but not sure whether it always happened or I only recently noticed it.

For take-off, full bleeds can be used or one can consider selecting packs off or APU bleed on to improve take-off performance. Selecting packs off without APU will also improve fuel burn. The normal procedure would then be to select pack 1 on after climb thrust is selected and pack 2 on after flap retraction, some operators just select both back on on thrust reduction. This has the effect of reducing fuel burn by 2 to 3 kg on an A320 increasing to 5 to 10 kg on an A340-500/600 for every takeoff.

With APU bleed the engine fuel burn will be decreased by the same amount. However with APU used from push back with 12 minutes taxi, the additional APU fuel burn is 30kg for an A320 and 60 to 70kg for an A340. In economic terms, the APU fuel and maintenance cost is largely offset due to decreased engine maintenance costs bleeds off (higher FLEX temp).

The main benefit is in the long term maintenance costs, the aircraft will be able to takeoff with a lower thrust setting, thus subjecting the parts to lower temperatures and stresses, which will extend the lift of the engine on the wing, or the number of parts that need to be replaced at overhaul, and lowers the probability of an engine failure.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
wilco737
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 12:57 pm



Quoting HAWK21M (Reply 15):

No, it's Mrs. Douglas feature... The MD11F tried to maintain the pressure and she can only achieve it, when closing the outflow valve... It all happens automatically...

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pilotpip
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 3:11 pm



Quoting HAWK21M (Reply 13):

What Type are you reffering too.
regds
MEL

MEL,

I'm in the EMB-145. I've seen other companies do it differently though.
DMI
 
wilco737
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 3:17 pm



Quoting Pilotpip (Reply 18):
I'm in the EMB-145

Thank god your are not ON the EMB-145 Big grin must be pretty windy up there  box 

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pilotpip
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 4:17 pm

You'd think it's windy inside too with all the noise.  Smile

Somebody forgot to tell those crazy Brazilians that when slapping a different wing, a couple fuselage plugs and a pair of turbofans on the Brazillia they may want to consider a redesign of the nose. It may be nice and quiet when it's in the lower 20s at 300kts true but it's pretty loud when it's faster.
DMI
 
wilco737
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 4:25 pm



Quoting Pilotpip (Reply 20):

yeah, everybody is talking about aircraft noise: I make it Big grin Big grin

Because of the noise in the cockpit and not having any noise canceling headsets I use earplugs Big grin Very helpful and quiet  Wink

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pilotpip
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RE: Airbus Air Conditioning During T/O

Wed Nov 14, 2007 9:53 pm

Oh my DC's work just fine. And you gotta love that mean green color.  Smile
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abnormal
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RE: Airbus Air Conditioning During T/O

Thu Nov 15, 2007 4:30 am



Quoting Zeke (Reply 16):



Quoting Zeke (Reply 16):
This has the effect of reducing fuel burn by 2 to 3 kg on an A320 increasing to 5 to 10 kg on an A340-500/600 for every takeoff.

With APU bleed the engine fuel burn will be decreased by the same amount. However with APU used from push back with 12 minutes taxi, the additional APU fuel burn is 30kg for an A320 and 60 to 70kg for an A340. In economic terms, the APU fuel and maintenance cost is largely offset due to decreased engine maintenance costs bleeds off (higher FLEX temp).

The main benefit is in the long term maintenance costs, the aircraft will be able to takeoff with a lower thrust setting, thus subjecting the parts to lower temperatures and stresses, which will extend the lift of the engine on the wing, or the number of parts that need to be replaced at overhaul, and lowers the probability of an engine failure

Excellent points Zeke. I get about the same numbers. Any issues re passenger comfort?
 
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zeke
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RE: Airbus Air Conditioning During T/O

Thu Nov 15, 2007 11:14 am



Quoting Abnormal (Reply 23):
Any issues re passenger comfort?

I don't think so, we have use said procedure for longer than I can to remember. For the pilots, and regular passengers, it is normal procedure. For new passengers, it is just the way things are done.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
abnormal
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RE: Airbus Air Conditioning During T/O

Fri Nov 16, 2007 3:50 am

Thanks Zeke. Interesting points I think I'm gonna mull over a bit. The hard part will be getting Stds on side I think.
 
Airbus_A340
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RE: Airbus Air Conditioning During T/O

Wed Nov 28, 2007 4:33 pm

Since my post, I've heard that in CX's Airbus Fleet Forum they discussed (that in the not too distant future) we will be doing Packs-ON for FLEX take-off's and Packs-OFF for TOGA take-offs.

I don't know the details as to why the change though.
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Fly2HMO
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RE: Airbus Air Conditioning During T/O

Thu Nov 29, 2007 1:20 am



Quoting Zeke (Reply 24):
For new passengers, it is just the way things are done.

But then when they turn the packs off I love it when you see half the hands in the cabin up in the air trying to adjust the gaspers, then suddenly a huge gust of air slaps them in the face when the packs are turned back on and then half the hands are up in the air again  Yeah sure
 
wowpeter
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RE: Airbus Air Conditioning During T/O

Thu Nov 29, 2007 3:46 pm



Quoting FLY2HMO (Reply 27):
I love it when you see half the hands in the cabin up in the air trying to adjust the gaspers

Simple, our lovely CX management decided not to install the gaspers in the first place... save weight and maintanence and no pax waving their hands before takeoff!  Wink
 
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HAWK21M
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RE: Airbus Air Conditioning During T/O

Thu Nov 29, 2007 3:50 pm



Quoting Wowpeter (Reply 28):
Simple, our lovely CX management decided not to install the gaspers in the first place... save weight and maintanence and no pax waving their hands before takeoff!

so they blanked out the ports of the PSU.Is it.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
wowpeter
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RE: Airbus Air Conditioning During T/O

Thu Nov 29, 2007 8:03 pm

Yup, just a blank white piece of plastic over the passenger service unit! I don't think there's any gaspers install in any CX plane (340, 744, 330... donno about the 777).

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