The De-Iceman Cometh

In both the United States and Canada, it took a horrific crash related to airframe icing to instigate a change in de-icing regulations.In Canada, it was the crash of the Fokker 28 commuter jet in 1989 that proved to be the impetus for changing de-icing regulations. In theUnited States, the crash of USAir flight 405 from LaGuardia on March22, 1992, instigated changes by the Federal Aviation Administration (FAA). In the aftermath of the crash, which resulted in 27 fatalities, the NTSB found that although the plane had been de-iced twice before leaving the gate, the time between the second de-icing and take-off(35 minutes) exceeded the "de-icing fluid safe holdover time" for that particular type of fluid. The result was a buildup of ice on the wings that resulted in aerodynamic stall shortly after lift-off. According to the post-accident report by issued by the NTSB, "the entire airline industry had been lax in training crews to detect hazards caused by ice and to compensate for such conditions."

These days, any second-guessing is removed from the equation, and the old gray area no longer exists. Both Canadian and American regulations now prohibit take-off when ice, snow, and frost is adhering to any critical surface of the aircraft, including lifting and control surfaces, wings and tail, and upper fuselage surfaces on aircraft withrear-mounted engines. The rule is known as the "clean aircraft concept."

The main exception to the new regulations allows a coating of frost up to one-eighth of an inch thick on wing lower surfaces in areas cold-soaked by fuel, between the forward and aft spars. De-icing also is not mandatory if the captain expects dry snow lying on top of a cold, dry, and otherwise clean wing to blow off during take-off. For aircraft types where the upper fuselage is a critical surface, a thin coating of frost is permitted in the area provided the deposit is thinenough that underlying surface features such as paint lines, markings, or lettering can be distinguished. Although pilots are in charge of deciding whether de-icing is needed, the "lead" ramp attendant can overrule a decision not to de-ice. Even flight attendants and passengers can voice concerns about the plane's de-icing efforts, although the final decision rests with the pilot.

Why a Clean Wing?

Many believe ice on the wings of an airplane is dangerous solely because of the additional weight on the aircraft. However, it is actually loss of lift and the resulting drag on the body of the aircraft that causes problems. Airplanes achieve lift when air flows smoothly over the contoured surface of the wing. If this streamlined flow is disrupted because of ice buildup, decreased lift occurs. A wing can lose 30 percent of lift with just a small accumulation of ice. The stallspeed, or the speed at which the wing ceases to be able to keep the aircraft aloft, can decrease by 15 percent with drag potentially increasing by 200 to 500 percent.

For example, a unique ice formation composed of clear ice that builds up into a single or double horn on critical surfaces can severelydisrupt airflow and increase drag 300 to 500 percent. Meanwhile, ice, frost, and snow that accumulate to the thickness of medium or coarse sandpaper on the leading edge and upper surface of a wing can reduce wing lift by as much as 30 percent and increase drag by 40 percent.

Toronto's Central De-Icing Facility

In Canada and similar locales, icing conditions can lurk nearly nine months of the year, so the de-icing checklist is always within reach because it's part of doing business. The old aviation adage, "If you think safety is expensive, try having an accident," is a rule to live by.

The CDF at Toronto's Airport is the largest de-icing facility in the world. Fully operational since the 1999-2000 cold season, this 65-acre "drive through airplane wash" consists of 6 huge bays capable ofhandling hundreds of aircraft daily. It has an official de-icing season of October 1-April 30. Many pilots jokingly refer to the CDF as the "central delay facility," but the fact that most pilots are paid by the minute takes the sting out of any wait. In addition, the short time it takes to spray a plane with de-icing fluid is insignificant compared with the potential for disaster if a pilot did not take the time to de-ice his or her aircraft.

Moreover, the CDF has actually reduced time between de-icing and takeoff because it was built closer to the runways and has increased overall throughput and improved turnaround times.

On the way to the CDF, after passengers have boarded the plane, pilots radio "pad control," which assigns the aircraft to a de-icing bay. Because this is a "live" or "engines running" operation, precise terminology and electronic signboards are used to eliminate any potential for accidents. Pilots then contact the "Iceman" in the de-icing control center, appropriately nicknamed the Icehouse.