Re: 747 "smoke" trail

Date:         24 May 99 01:52:16 
From:         "J. W. Dawson" <hatcat@frontiernet.net>
Organization: Frontier GlobalCenter Inc.
References:   1 2
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Edward Lee wrote in message ...
>>A couple of days ago, I was looking at a 747-400 pass over my house at
>>about 5000 feet on landing vectors to SFO.  While watching, I noticed a
>>white stream of smoke or mist starting to come from the tailcone area.
>>This continued for a short period of time, leaving a 10-15
>>airplane-length trail in the sky.  I assume this smoke had something to
>>do with the APU.  However, I have watched a *lot* of jets and never seen
>>this before.
>
>I've been on an B747-400 full loaded taking off from LAX for
>Taipei, Taiwan, the mist generated from the wing due to high
>moisture and high differential pressure between the upper and
>lower surface of the wing were so intense that I couldn't see
>through it. I guess it might be the same thing that you saw
>coming out from the big jet.

I believe you are seeing APU smoke. I've watched a lot of planes myself
and I have noticed this from time to time. I don't know if it's a
characteristic of a particular model of APU or if it's just an
occasional effect with no particular connection with the hardware.

Perhaps it's a bit of smoke due to leftover fuel burning off from the
last shutdown or a bit of oil burning off from a leaky seal. Having seen
a "torching" APU start a few times on the ground I've wondered if the
smoke might be from a similar situation inflight.

J.W. Dawson