B727 APU starting problem
Thread Starter
Joined: Oct 2004
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From: Dark Africa
B727 APU starting problem
Morning guys, looking for info please to sort out a problem.
After long flight our APU does not want to start after landing. Left overnight it will start normally. Looks like coldsoaking causing it not to start. What could the problem be?
Thanx
Bleedvalve
After long flight our APU does not want to start after landing. Left overnight it will start normally. Looks like coldsoaking causing it not to start. What could the problem be?
Thanx
Bleedvalve
Thread Starter
Joined: Oct 2004
Posts: 42
Likes: 0
From: Dark Africa
Starter kicks in.
Will only go out at about 45 sec, sometimes not.
EGT rise and keep on rising.
It seems that the whole cycle just takes too long. Starter takes too long to kick out and EGT keeps rising.
Will only go out at about 45 sec, sometimes not.
EGT rise and keep on rising.
It seems that the whole cycle just takes too long. Starter takes too long to kick out and EGT keeps rising.
Joined: Aug 1998
Aviation Qualifications: ATPL
Posts: 6,623
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From: Ex-pat Aussie in the UK
If the battery voltage drops below 18V or so during the start, some of the relays fail to sequence. Select and watch the Batt voltage during the start, and see if the cold has affected the batteries? If the voltage is low the system will prevent the APU from operating due to no fire protection.
(Note: this is (an educated) guess!
)
(Note: this is (an educated) guess!
)
Joined: Apr 2008
Posts: 461
Likes: 1
From: A tropical island.
Kind of slim on the details there, how is the start cycle going?
Is it just refusing to even crank or is it not lighting off?
If it's cranking how much time are you giving it before turning it off?
Etc. Etc.
I've seen water get into strange places in 727s, might be some freezing the fuel valve shut in flight. I have this happen often on a crossfeed valve in one plane.
Is it just refusing to even crank or is it not lighting off?
If it's cranking how much time are you giving it before turning it off?
Etc. Etc.
I've seen water get into strange places in 727s, might be some freezing the fuel valve shut in flight. I have this happen often on a crossfeed valve in one plane.
Usual disclaimers apply!
Joined: Nov 1999
Posts: 843
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From: EGGW
What oil does it take? We got around a lot of 'cold soak' issues on the 747 classic by changing the oil from Mobil jet 2 to Castrol 325. The lower viscosity allowed the APU to spin up faster. (Don't think 325 is still available so we use Shell 390 on the 744)
Joined: Apr 2008
Posts: 461
Likes: 1
From: A tropical island.
There's lots of 727s that start. A few DC-6s 7s even, a bunch of DC-3s too, those old American built planes outlast a lot of the stuff from other places, so don't be so surprised that theyre still running.
