The De-Iceman Cometh

Once the aircraft is in position to receive the de-icing spray, a machine called the Denmark Vester-gaard Elephant Beta springs into action. Smaller planes might need only one Beta for de-icing, while larger jumbo jets might need as many as four. The CDF has 27 Beta machines, each of which costs about one million Canadian dollars, or about $876,000 U.S. The iceman tells the pilot the exact time de-icing started, the type of fluid used, and when the vehicles have retreated to their safety zones. A safety zone is an area ensuring a safe distancebetween the aircraft and de-icing vehicle. The de-icing vehicles must be behind these lines before an aircraft can exit the de-icing area.

While many airports still employ manually operated "cherry pickers" staffed by ground crew who must brave the bitter winds and back spray, the CDF machines are operated remotely by the Iceman from a heated enclosed cab. They are armed with de-icing fluid, nozzles, whisker-like probes to prevent aircraft contact, and a telescopic boom to reach distant spots and critical flight surfaces.

The de-icing procedure involves spraying fluids that remove or prevent ice build-up all over the aircraft. Strictly speaking, de-icing refers to the removal of existing ice, while anti-icing prevents new ice from forming. Made up of combinations of glycol and water, de-icing and anti-icing fluids come in different varieties that each serve a specific function. The difference between the types of fluid is the"holdover time," or the time from when de-icing commences to the time the airplane must be airborne, based on temperature, precipitation rate, and type. For example, with Type I fluid at -3[degrees]C in light snow, the holdover time is about 40 minutes. For most operations, the de-icing Type I fluid is used to remove the snow and ice, and Type IV is used to prevent further adhering of ice.

As an airplane is being de-iced, all of the extraneous fluid that falls off the aircraft is collected in holding tanks to ensure compliance with environmental regulations, as de-icing fluid can be a hazard to nearby bodies of water. The tanks can hold up to 3,434,237 gallons of reclaimed fluid. Some of the spent fluid is used to make car windshield wash and engine coolant, but it cannot be re-used for airplane de-icing because possible degradation of the fluid means that its effectiveness cannot be guaranteed. Air Canada prohibits the use of recycled fluid.

According to Joe Forbes, Senior Manager of De-icing Operations at the Greater Toronto Airports Authority, a typical Airbus A320 that holds about 150 passengers in light snow conditions requires 80 gallonsof Type I fluid and 69 gallons of Type IV fluid, with actual de-icing time taking just over 4 minutes. The throughput time at CDF for an Airbus is an amazing 12 minutes.

At more than four dollars per gallon for Type I and double that for Type IV fluid, de-icing an airplane is an expensive proposition. During one 3-day ice storm in April 2003, the CDF used 396,258 gallons of de-icer in a single day, the highest amount in the facility's history. At one point the CDF actually ran out of de-icing fluid and scrambled to get more from Chicago, Denver, Forth Worth, and Montreal, Forbes said. One truckload of 4,497 gallons that was brought in from Chicago was dispensed on a single jumbo aircraft. Because de-icing fluid has a limited shelf life once it has been sprayed on an aircraft, pilots consult onboard charts and consider current temperatures and types of precipitation to determine how long they have before they mustget airborne. If the take-off is delayed for any reason, they may need to head back for a re-spray.

In-Flight Ice Formation

Airframe ice does not occur only on the ground. Although there exist some 30 variables when it comes to the formation of ice on an aircraft in flight, the two primary factors are visible moisture (clouds)and freezing temperatures. Clouds contain supercooled water droplets, which are composed of water in a liquid state, even though temperatures are below freezing. When a super-cooled droplet strikes an aircraft, it freezes upon impact. To prevent such freezing, airliners are outfitted with heated leading edge wings that are warmed by the hot air bled from engines. Heated windscreens, instruments, and engine probes and intakes, as well as continuous use of engine igniters, all aid in the battle against ice accumulation.