Re: Snow on wings

From:         ehahn@bass.mitre.org (Ed Hahn)
Organization: The MITRE Corporation, McLean, Va.
Date:         02 Jun 96 23:01:50 
References:   1
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In article <airliners.1996.682@ohare.Chicago.COM> whodgins@axess.com (W. Hodgins) writes:

> Some time ago I was a passenger on a DC-9 flight out of Toronto in
> January as I recall. Looking out the window, I noticed a fair amount
> of snow on the wings...it was not removed and the aircraft took off
> with snow blowing off the wings as speed increased.
> I used to fly light aircraft in the early 70's and if I recall
> correctly we were supposed to ensure that nothing, not even frost,
> should be allowed to accumulate on the wings.
> What is the criteria for large jets...is an accumulation of light snow
> normally acceptable ?

Unless there was de-icing fluid on the wings, the scenario you
described would certainly appear to be of questionable legality (and
potentially even unsafe).  However, not knowing the specifics, I
wouldn't feel comfortable making any further speculation, as the new
Type II de-ice (anti-ice) fluids have very good performance even after
several minutes in heavy snow.

Aircraft shouldn't have any debris at all on their wings when taking
off, as the aerodynamics during takeoff (high CL, flaps position,
etc.) are critical.  Any debris on the top surface of the wing can
potentially cause severe degradation of the lift performance in a
takeoff situation.  (Even frost can be a significant factor in whether
the airflow will behave nominally.)

Even with de-icing fluids, airlines currently go through significant
pain to ensure that the combination of preciptation rate, outside
temperature, de-ice fluid composition and temperature, and time will
make the de-ice fluid capable of performing its job.

ed

--------   Ed Hahn | ehahn@mitre.org | (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.