Re: Three questions.

From: (Kim Hackett)
Organization: Your Organization
Date:         27 Jun 96 12:42:10 
References:   1
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>1. A Singapore airlines A340 moved onto the runway and took off, as an
>Ansett 727 was approaching. The 727 had to abort and go around. Is this a
>mistake by AirTraffic control, does it happen often and how annoyed would
>the 727 crew have been?
>2. A Qantas 747-400 started its takeoff run and then stopped, moved off
>the runway and stopping and starting a few times (ie: winding up
>the engines) before moving into the queue again and taking off normally.
>What could have been the problem?
>3. An Evergreen cargo 747 (200?) was about to take off. There was
>substantial vapour coming from the left wingtip. It took off and the
>vapour increased. After takeoff vapour was coming from the right hand
>wingtip as well, obscuring the plane. Was this fuel, and if so, is it not
>dangerous? Why was it being released?
1) It could be a mistake by ATC for spacing the 727 too close.  It could
be that the A340 took longer than anticipated on the runway.  I was on
a DC-10 into O Hare once when we did a go around.  The pilot said that
the aircraft ahead of us had not cleared the runway for us to land safely.
2) The pilot may have had an engine instrument warning or indication that
something was unusual.  Hard to guess what it could be.
3) It most likely was not fuel.  Many times during high humidity conditions
the wing tips generate >visible< vortices because the higher pressure air
on the bottom of the wing is circulating to the top of the wing where it
is lower pressure.  Under certain conditions of high humidity, or dew point
and temperature are close, the change in pressure is enough to condense
the water out of the air.  These vortices always exist, but are visible
during these conditions.