Re: Deicing

Date:         25 Jan 98 03:27:23 
From:         "David E. Pearce Jr." <david.e.pearce@ast.lmco.com>
Organization: Lockheed Martin
References:   1
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Ken S wrote:
> I was wondering if any one can help explain the FAA rational for deicing
> aircraft. I have seen aircraft deiced when the outside air temp was -10c
> and very light snow falling. Now I understand the Clean aircraft concept
> yet it seems to me that this snow (maybe enough to leave a trace after
> several hours) poses no threat to the aircraft. Yet because our ops
> specs call for a "clean airplane" we must de-ice.

Airline pilots are not test pilots. If specific icing conditions are not
enveloped in testing, then a flight into those icing conditions are test
flying. It is difficult to quantify snow and icing conditions on an
aircraft, so instead they prep the aircraft to known conditions (ie
deice it).

Also, the aircraft surface could be above freezing and the snow falling
could be melting  and draining to a lower and colder part of the
aircraft and freezing. The snow could melt on the top surface of the
wing due to warm fuel and flow down to the leading edge, which being
thin metal without fuel behind it is colder, and refreezing. Ice on the
leading edge of a wing is not a good place to have it as it can upset
the flow over the entire rest of the wing upper surface.