Vs744 From United Kingdom, joined Aug 2001, 677 posts, RR: 1 Posted (5 years 6 months 2 weeks 7 hours ago) and read 4188 times:
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.
FBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 7 Reply 1, posted (5 years 6 months 2 weeks 5 hours ago) and read 4158 times:
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.
RoseFlyer From United States of America, joined Feb 2004, 8739 posts, RR: 52 Reply 2, posted (5 years 6 months 2 weeks 3 hours ago) and read 4142 times:
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 From United Kingdom, joined Dec 2000, 153 posts, RR: 0 Reply 3, posted (5 years 6 months 2 weeks 2 hours ago) and read 4122 times:
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.
Airbus_A340 From Hong Kong, joined Mar 2000, 1554 posts, RR: 21 Reply 5, posted (5 years 6 months 1 week 6 days 22 hours ago) and read 4066 times:
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.
WILCO737 From Greenland, joined Jun 2004, 8473 posts, RR: 78 Reply 6, posted (5 years 6 months 1 week 6 days 22 hours ago) and read 4050 times:
AIRLINERS.NET CREW HEAD MODERATOR
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
Modesto2 From United States of America, joined Jul 2000, 2634 posts, RR: 6 Reply 7, posted (5 years 6 months 1 week 6 days 22 hours ago) and read 4050 times:
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.
HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Reply 8, posted (5 years 6 months 1 week 6 days 14 hours ago) and read 3946 times:
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.
CoolGuy From United States of America, joined Jan 2005, 410 posts, RR: 0 Reply 10, posted (5 years 6 months 1 week 6 days 1 hour ago) and read 3832 times:
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 From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 11, posted (5 years 6 months 1 week 5 days 12 hours ago) and read 3758 times:
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.
Pilotpip From United States of America, joined Sep 2003, 3082 posts, RR: 12 Reply 12, posted (5 years 6 months 1 week 4 days 21 hours ago) and read 3688 times:
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.
WILCO737 From Greenland, joined Jun 2004, 8473 posts, RR: 78 Reply 14, posted (5 years 6 months 1 week 4 days 8 hours ago) and read 3593 times:
AIRLINERS.NET CREW HEAD MODERATOR
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 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
Zeke From Hong Kong, joined Dec 2006, 7725 posts, RR: 73 Reply 16, posted (5 years 6 months 1 week 4 days 5 hours ago) and read 3574 times:
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
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...
Pilotpip From United States of America, joined Sep 2003, 3082 posts, RR: 12 Reply 18, posted (5 years 6 months 1 week 4 days 2 hours ago) and read 3550 times:
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.
Pilotpip From United States of America, joined Sep 2003, 3082 posts, RR: 12 Reply 20, posted (5 years 6 months 1 week 4 days 1 hour ago) and read 3525 times:
You'd think it's windy inside too with all the noise.
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.
Pilotpip From United States of America, joined Sep 2003, 3082 posts, RR: 12 Reply 22, posted (5 years 6 months 1 week 3 days 19 hours ago) and read 3479 times:
Oh my DC's work just fine. And you gotta love that mean green color.
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?
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
25 Abnormal: Thanks Zeke. Interesting points I think I'm gonna mull over a bit. The hard part will be getting Stds on side I think.
26 Airbus_A340: 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-
27 FLY2HMO: 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
28 Wowpeter: 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 b
29 HAWK21M: so they blanked out the ports of the PSU.Is it. regds MEL
30 Wowpeter: 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...
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