How and why airports de-ice an airplane
Waiting to take off at Vancouver International Airport last month, I watched from my window seat as the ground crew de-iced one of the wings of my airplane. It got me wondering: what exactly is this strange-looking process, and how does it work?
Later, I called up Brett Patterson, YVR’s director of airside operations, to find out. “When you’re inside the plane, it looks like you landed on Mars and they’re doing weird things to the aircraft,” he agrees with a laugh.
Patterson says the de-icing season at YVR runs from October 1 to April 30, and that planes are treated when there are frosty or snowy conditions. “A layer of frost on the upper wing can disrupt the flow of air and affect lift,” he explains. “De-icing is to remove that layer of frost…The airplane needs to be clean to generate lift and fly safely.”
Pilots check for frost on the wings and the horizontal part of the tail during their routine pre-flight walk around the plane, and if in doubt, they order a physical inspection. “If there’s freezing precipitation, you’re going to get de-iced,” Patterson says. “If it’s a frosty morning, there’s a good chance you’re getting de-iced.…It depends on the frost that’s on the aircraft, and it also depends if your aircraft was sitting there when frost was forming…or if the plane just came in.”
At YVR, the de-icing pad is located between the main terminal and the runways. Two to eight trucks do the job, depending on the size of the aircraft. Raised on a scissor lift, the operator sprays the wing with a hot mixture of water and glycol, which is pink or orange in colour. The steamy operation dissolves the frost and prevents it from again adhering to the wing.
According to Patterson, glycol is in the same chemical family as your car’s windshield washer fluid. It’s biodegradable, and when it drips off the plane, it goes into a drainage system that takes it to a storage lagoon and then a sewage treatment plant.
Another kind of truck is controlled by an operator in a cab, who uses a boom to spray the liquid. The truck has a set of “whiskers” that hover near the wing and look like neon orange deely boppers. These sensors prevent the truck from hitting the wing by warning the operator if the truck is getting too close.
When there’s snow as well as frost, the operator will use a thicker, green glycol-based anti-icing fluid. This clings to the wing and buys the clean aircraft more time to get to the runway.
So what happens to the snow on top of the plane? If there’s not much, Patterson likens it to the roof of a house: the snow melts because it’s warm inside, rather than sticking like it does to the wings.
However, in heavy snowfall the whole plane may be de-iced. “That’s to make sure the plane is clean, and it will be efficient and fly safely,” he says. “In frost, it’s just the wings that are critical.”
During the de-icing process, pilots talk to the ground crew and calculate the amount of “holdover time” they have to take off before the de-icing effects wear off. That time “depends on the conditions and the amount and intensity of the snowfall”, Patterson says. If there’s a backup in runway traffic that exceeds this holdover time, the plane will need another treatment.
Once airborne, the situation changes. “When you’re travelling at 800 kilometres an hour, very little is going to stick to you,” Patterson explains. “Plus, the wing is designed to shed at-velocity snow and ice.”
Patterson compares the process to driving your car in the snow. “You’ve cleared your car off. As long as you keep driving, the wind is blowing everything off. You’re not getting a buildup of snow on the front of your car. Your car’s warmed up, there’s a defroster on the windshield. It’s the same concept.”