NTSB Safety Alert SA-006 - Aircraft Ground Icing

Aircra ft Ground Icing

Pilots urged to beware of aircraft upper wing

surface ice accumulation before takeoff

The problem:

• Fine particl es of frost or ice, the size of a grain of table salt and distributed as spars ely as one per

square centimeter over an airplane wing’s upper surface, can destroy enough lift to prevent a

plane from taking off.

• Virtually imperceptible amounts of ice on an aircraft wing’s upper surface during takeoff can result in

significant performance degradation.

• Small, almost imperceptible amounts of ice distrib uted on an airplane’s wing upper surface cause

the same aerodynamic penalties as much larger (and more visible) ice accumulations.

ƒ

Small, almost

imperceptible

accumulations

• Small patches of ice or frost can result in localized, asymm etrical stalls on the wing, which can

result in roll control problems during liftoff.

• It is nearly impossible to determine by visual observation alone whether a wing is wet or has a thin

film of ice. A very thin film of ice or frost will degrade the aerodynamic performance of any airplane.

• Ice accumulation on the wing upper surface may be very difficult to detect from the cockpit, cabin,

or front and back of the wing because it is clear /white.

• Accident history shows that nonslat ted, turbojet, transport -category airplanes have been involved

in a dispro portionate number of takeoff acciden ts where undetected upper wing ice contamination

has been cited as the probable cause or sole contributing factor.

• Most pilots understand that significant visible ice contam ination on a wing can cause severe

aerodynamic and control penalties, but it is apparent that many pilots do not recognize that minute

amounts of ice adhering to a wing can result in similar penalties.

• Despite evidence to the contrary, these belie fs may still exist because many pilots have seen their

aircraft operate with large amounts of ice adheri ng to the leading edges (including the dramatic

double horn accretion) and consider a thin layer of ice or frost on the wing upper surface to be

more benign.

SA-006 December 2006, revised December 2015 What should pilots know and do about airplane icing before takeoff?

• Pilots should be aware that no amount of snow, ice or frost accumulation on the wing upper

surface should be considered safe for takeoff. It is critically important to ensure, by any means

necessary, that the upper wing surface is clear of contamination before takeoff.

• The NTSB believes strongly that the only way to ensure that the wing is free from critical

contamination is to touch it.

• With a careful and thorough preflight inspection, including tactile inspections and proper and liberal

use of deicing process es and techniques, airplanes can be operated safely in spite of the

adversities encountered during winter months.

• Pilot should be aware that, even with a wing inspection light, the observation of a wing from a 30- to

40-foot distance through a window does not constitu te a careful examination.

• Pilots may observe what they perceive to be an insignificant amount of ice on the airplane’s

surface and be unaware that they may still be at risk beca use of reduced stall margins resulting

from icing-related degra ded airplane performance.

• Depending on the airplane’s design (size, high wing, low wing, etc.) and the environmental and

lighting conditions (wet wings, dark night, dim lights, etc.) it may be difficult for a pilot to see frost,

snow and rime ice on the upper wing surface from the ground or through the cockpit or other

windows.

• Frost, snow, and rime ice may be very difficult to detect on a white upper wing surface and clear

ice can be difficult to detect on an upper wing surface of any color.

• Many pilots may believe that if they have suffic ient engine power available, they can simply “power

through” any performa nce degradation that might result from almost imperceptible amounts of

upper wing surface ice accumulati on. However, engine power will not prevent a stall and loss of

control at liftoff, where the highest angles of attack are normally achieved.

• Some pilots incorrectly believe that if they cannot see ice or frost on the wing from a distance, or

maybe through a cockpit or cabin window, it must not be there – or if it is there and they cannot

see it under those circumstances, then the accumulati on must be too minute to be of any

consequence.

Need more information?

• Crash During Takeoff in Ici ng Co nditions, Canadair, Ltd., CL -600-2A12, N873G, Montro se, CO, Nove mber 28, 2 004.

Aircraft Accid ent Report N TSB/AAB -06/03: www.ntsb.g ov/publictn/2006 /AAB0603.htm

• Epps Air Serv ice, Cha llenger 604, Birm ingham Internatio nal Airport, Birmi ngham, UK, Ja nuary 4, 20 02. Air Accid ents

Branch (AAIB), Departm ent of Transport, UK. Air craft Accid ent Report 5/ 2004 (EW/C20 02/1/2):

https://assets.digital.cabinet -office.gov.uk/media/5422f61940f0b61346000619/5 -2004_N90AG.pdf

• NTSB recommen dation letter issu ed as a re sult of 26 Ce ssna 208 i cing-related in cidents and ac cidents:

www.ntsb.gov/Recs/lett ers/2004/A04_64_67.pdf

• Takeoff Stall in Icing Co nditions, USAir flight 405, F okker F-28, N4 85US, LaGuar dia Airport, Flushing, NY, March 22,

1992. Aircraft Accid ent Re port NTSB/AAR -93-02:

http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9302.pdf

• Loss of Contr ol on Takeoff, Ry an Internat ional Airlines, DC-9-15, N 565PC, Cleve land-Hopkins Inter national Ai rport,

Cleveland, OH, Februa ry 17, 1991. Air craft Accid ent Re port N TSB/AAR -91/09:

http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9109.pdf

• Crash During Takeoff in Ici ng Co nditions, C ontinental Air lines, DC -9-14, N26 TX, Staplet on Internati onal Airport,

Denver, CO, November 15, 19 87. Aircraft Accident R eport N TSB AAR -88/09:

http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR8809.pdf

• NTSB website: http://www.ntsb.gov