APU Master ON before takeoff
What are the consequences of having the APU master ON before takeoff, and back OFF sometime after?
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Originally Posted by MD83FO
(Post 10593725)
What are the consequences of having the APU master ON before takeoff, and back OFF sometime after?
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Originally Posted by Roj approved
(Post 10593758)
The flap will be open
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Originally Posted by MD83FO
(Post 10593725)
What are the consequences of having the APU master ON before takeoff, and back OFF sometime after?
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Originally Posted by vilas
(Post 10594097)
And why would you do that?
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If someone is actually putting the master switch on without the APU running, then I'm guessing they want to get a leg up on a possible APU start after takeoff (engine failure, generator drops off line, etc) since they won't have to wait for the ram air door to cycle open |
Maybe the OP pressed the APU master switch by mistake before T/O and wonders if there are any consequences?
Many moons ago, at TOD inbound to Heathrow in our BAe146, I noticed the APU was still running. Ooops ! :) |
Originally Posted by vilas
(Post 10594234)
I doubt if this could be the reason. EFATO is not such a deadly emergency that you require APU in a split second. ECAM or STATUS don't even mention APU start. Starting of APU is only mentioned in FCOM Abnormal procedure There cannot be procedures for phobias.
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Originally Posted by Uplinker
(Post 10594258)
Many moons ago, at TOD inbound to Heathrow in our BAe146, I noticed the APU was still running. Ooops ! :)
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Originally Posted by matsemann
(Post 10594325)
All 5 of them?
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Originally Posted by MD83FO
(Post 10593725)
What are the consequences of having the APU master ON before takeoff, and back OFF sometime after?
1) The flap will be open. Looking at the MEL items where the APU is left running, there may be no performance penalty. Hm, actually it would not be thrusting nor sucking even a little, with the open inlet in this scenario causing net parasitic drag - so perhaps check with CDL and the OEM is needed to formally tick all the boxes. 2) Some less insightful people might think it is actually a good idea. 🤔 3) Something happens in the electric system with Master SW on (cue emerg elec proc), so worthwhile researching if that is relevant and with consequences or not. 4) the wear of the switch push-button and system contractors is increased. (recorded in order of appearance). |
Originally Posted by matsemann
(Post 10594325)
All 5 of them?
Remind me how many successful civil jet airliners Norway has designed and built ? :) |
Originally Posted by Uplinker
(Post 10594766)
Ha ha !
Remind me how many successful civil jet airliners Norway has designed and built ? :) |
Originally Posted by Tomaski
(Post 10594127)
If someone is actually putting the master switch on without the APU running, then I'm guessing they want to get a leg up on a possible APU start after takeoff (engine failure, generator drops off line, etc) since they won't have to wait for the ram air door to cycle open..
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On a late 80's designed jet, dropping 1 ENG GEN cuts the IFE, aft galley and half of the fwd galley. There one oven and one coffee-maker remain operative - guessing that without them it would be a real emergency.
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Been away from the MD-80 for awhile, but what I recall from this situation is the concern over something happening to that single engine-driven generator until the APU started. With one generator, the APU had an electric starter assist. Without, you were down to a windmilling start (to preserve the battery) which could take a while if you were not well inside the starting envelope. Not a huge problem in VMC conditions, but IMC was a different story. |
thanks for the injunctions, my train of thought is, ok, mitigation of bird damage on initial climb when warranted, accelerate above 3000' where most bird impacts occur, secondly be ready for a dual engine failure and emergency electrical config by having the APU ready to start, it doesn't seem to affect in any way normal operation.
the A350 starts the APU automatically when needed. |
Originally Posted by MD83FO
(Post 10597174)
thanks for the injunctions, my train of thought is, ok, mitigation of bird damage on initial climb when warranted, accelerate above 3000' where most bird impacts occur, secondly be ready for a dual engine failure and emergency electrical config by having the APU ready to start, it doesn't seem to affect in any way normal operation.
the A350 starts the APU automatically when needed. |
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