Winter is upon us, and among other things, that means American Airlines’ de-icing efforts are gearing up. Since safe flight depends on an aircraft having its wings, engines, and control surfaces free of snow, frost, sleet, freezing rain, or ice, we spend a lot of time, money, and effort during the winter months keeping these surfaces of our aircraft “clean.” While we are usually able to accomplish this and still depart on time, safety is always our top priority, and thus delays are sometimes unavoidable.
Ice and snow can potentially distort the curvature of the wing’s upper surface and disturb the normal airflow, thus interfering with an airplane’s control mechanisms. To keep this from happening, we “de-ice” to remove already-accumulated environmental contaminants and “anti-ice” to prevent subsequent accumulation. These processes involve spraying fluids of various content and viscosity on the control surfaces of the airplane’s wings and tail, on the wings themselves, and, in some circumstances, on the engine inlets and fuselage. Most times, a single application does the job, but in heavy weather, or when we expect a longer-than-normal wait between de-icing and takeoff, it’s sometimes necessary to apply a second, thicker compound to prevent any new accumulation.
The fluids we use consist of combinations of ethylene or propylene glycol, hot water, and several additives. Referred to as Type I, Type II, and Type IV, these fluids keep new ice or snow from building up on the airplane’s critical surfaces for varying “holdover” periods (the time varies according to temperature, precipitation density, and aircraft type). In sufficient quantities, these substances can be hazardous to the environment and must be handled according to strict guidelines. The airport’s collection capabilities determine where an aircraft can be de-iced. At some airports, this is done at a special area near the end of the runway. At others, de-icing is accomplished at the gate or another specified location.
When precipitation and the interval between treatment and takeoff exceed the allowable holdover time for the situation at hand, the aircraft must be checked again no more than five minutes before takeoff. Depending on the type of airplane and the configuration of the wing, Federal Aviation Administration regulations allow the recheck to be done either visually, by the pilots from inside the airplane, or physically, by specially trained ground personnel outside who communicate with the pilots during and after the inspection.
Once airborne, the airplane is capable of keeping its critical surfaces clear of contamination through special heaters in strategic locations. The temperature, airflow, and humidity at higher cruise altitudes often cause moisture to sublimate, or pass directly from a solid to a vapor state, thus cleaning the surfaces naturally.
The de-icing process, although conceptually simple, is complex in practice. To ensure that our flight and ground personnel understand it fully, we give our people extensive training in such subjects as the aerodynamic effects of snow and ice, the chemical properties of the fluids used, and the minutest details of our procedures. Everyone gets both initial and recurrent training. As you might imagine, all of this is very expensive. Inevitably, some delays will occur as we do the work necessary to ensure a safe flight. The good news, however, is that increased knowledge, better compounds, and our carefully followed procedures have made winter flying safer than ever.
If you get caught in a weather delay this winter, I’m sure you’ll appreciate the many people working hard behind the scenes to make sure your aircraft is ready to fly safely. On their behalf, and on behalf of all of us at American Airlines, thanks for flying with us, and Happy Holidays!
GERARD J. ARPEY
President & CEO