|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...
|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?
|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.
|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
|Quoting Abnormal (Reply 23):|
Any issues re passenger comfort?
|Quoting Zeke (Reply 24):|
For new passengers, it is just the way things are done.
|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!
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