Bio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7 Posted (11 years 1 month 3 weeks 2 days 5 hours ago) and read 1321 times:
In a recent post I read an FBU 4ever post where he stated MD80s performed APU windmill starts. Is this also a practice on larger aircraft as the Airbusses and Boeings? And also, is the procedure for these starts just opening the APU intakes?
Cdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 28 Reply 1, posted (11 years 1 month 3 weeks 2 days 3 hours ago) and read 1292 times:
Of the aircraft I've had the opportunity to work, the MD80 is the only one with this feature. Not on the 737,757,767,777.
If the MD80 loses L & R AC Power inflight, the starter is disabled. The Ram Air Doors open fully and allow the APU to windmill start.
The 737 starter is available as long as the battery has power. The 757, and B767 starters are available as long as both batteries have power. The B777 is similar to the 757/767, but it has an additional pneumatic starter for the APU.
As for the start procedure, you just start the APU door normally. The RAM doors switch is supposed to be in normal for the start, and it will go to the RAM position for the start. And with aircraft going as fast as it is, the ram air gets the APU moving, as I understand it fairly quickly.
Bio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7 Reply 2, posted (11 years 1 month 3 weeks 2 days 3 hours ago) and read 1290 times:
Very interesting Cdfmxtech, I wonder why Boeings don't have this mechanism. It could be a last resource in case of full electrical loss I assume!
>>>The B777 is similar to the 757/767, but it has an additional pneumatic starter for the APU.
Does this mean there has to be a compressed air reserve? or simply that engine bleed air is ducted all the way to the APU turbine?
Cdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 28 Reply 3, posted (11 years 1 month 3 weeks 2 days 2 hours ago) and read 1274 times:
Well, first off, in a COMPLETE electrical loss, you won't get an -80 APU started either. Needs the battery.
It was pretty smart of Douglas (Did I say that). Disabling that APU starter can save use on the battery during an emergency and give u a couple of extra minutes.
As for the B777, it uses the pneumatic starter whenever the manifold is pressurized...be it by engine bleeds or ground air carts. There is no compressed air reserve.