Re: Caution: (757) Wake Turbulence ?

From:         moersch@aphrodite.world (Jeffrey E. Moersch)
Organization: /home/astrosun/moersch/.organization
Date:         13 Jan 94 05:07:22 PST
References:   1 2
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>> They're saying separation should be increased to about five miles and 
>> only mentioned 757s, no other types or generalizations.  Is there anything 
>> unique about that aircraft that it creates a particularly strong (or 
>> longer lasting) wake?  Or was the statement made only to focus on the 
>> situation at hand?
> 
> Yes, the 757 appears to generate wake turbulence which is much more
> severe than would be expected for an aircraft of its weight.  (Remember

The Orange County Register did a story on the 757's wake several days
after the crash.  Evidently there was a study done (I forget who did
it - maybe the FAA) that showed the 757 leaves a more "dangerous"
(quantified as the vertical wind speed of the vortices) wake than
*even a 747 or a C-5A Galaxy*!  The number that sticks in my memory
for the 757 was something like 338 f.p.s. vertical wind speed, while
most of the heavies were down in the 200's and smaller jets in the
100's.

I got my PP-ASEL at SNA, and it makes perfect sense to me that if a
757 wake accident was going to occur, that's where it would happen.
The traffic level is high, there is a mix of big iron and GA planes,
and the two runways are close together with parallel approaches going
on all the time (although in this case, I'm sure the Westwind would
have been landing on the same runway as the 757).  I can remember at
least a couple times when I felt the remains of a vortex rock the
little 152 I trained in, even when following all the usual
wake-avoidance rules of thumb.  I never hit anything extreme though
(probably *because* we were careful to follow those rules).

Jeff Moersch, PP-AMEL
Astronomy and Space Sciences
Cornell University
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