Re: S80 Ground Checks

From: (Ed Hahn)
Organization: The MITRE Corporation, McLean, Va.
Date:         09 Apr 96 14:22:49 
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  or MIME structure (Mark Misener) writes:

> Last week I was on an American Airlines S80 Chicago to San Diego (and
> return). I noticed that the ground crew were putting up ladders against
> the leading edge of the wing near the wing-root, and were running some
> kind of plastic brush, or something back and forth (from lead edge to
> trail edge). I couldn't see exactly what they were doing from where I was
> sitting, but, I've been on plenty of flights, and I don't recall seeing
> anyhting like it before. On top of that, I was talking to a friend of
> mine, and he said that he was also on an S80 recently, and observed the
> same thing. He also mentioned that he noticed a parked S80 with the skins
> removed at the wing-roots. Does anyone know what was going on?

My guess is that these would have something to do with the MD80
wing-ice detection/prevention modifications.

It turns out that MD80s can experience a form of wing icing, even if
the temperature on the ramp is near 70deg F.  The problem is that, on
a long flight, fuel in the wings can get very cold.  Upon landing
(especially in humid air) while sitting on the ramp, ice can form on
the wings where the cold fuel is adjacent to the skin (at the wing
root).  There have been incidents where this ice has broken off on
takeoff roll, was ingested by the engines, and caused damage.

An Airworthiness Directive (AD) was issued which initially mandated
the installation of triangles with tufts of cord on them - the theory
being that the crew could more easily see the presence of ice with the
cords.  Another carrier came up with an alternate means of compliance
to the AD, which involved using some specially textured paint applied
in a striped pattern over the wing.  The paint appears different when
clean vs. when covered with ice.  A third means of compliance was to
install a fuel circulation system which would continuously move the
fuel around while in flight, so that none of it would get cold enough
for this to be a problem.

Hope this helps,

--------   Ed Hahn | | (703) 883-5988   --------
The above comment reflects the opinions of the author, and does not
constitute endorsement or implied warranty by the MITRE Corporation.
Really, I wouldn't kid you about a thing like this.