Ice Ice… De-ice
If you happen to travel during the winter break, you probably notice that when you finally do leave the gate (after being delayed for what seems like forever), the aircraft heads to what looks like a ‘car-wash’ rather than proceeding to the runway for take-off. Well, this ‘car-wash’ is called de-icing and it’s a crucial procedure in aviation.
In aviation, ice is bad news. Well, the easiest explanation is that it adds on to the weight of the aircraft, hence, decreasing its performance…well that’s true but it’s not the whole story. When air flows over the smooth surface of the wing, the airplane achieves lift and is able to take-off. The accumulation of ice on the surface of the wing disrupts this airflow and the airplane loses its lift. The result of the loss of lift is not always pleasant. This was illustrated in a number of tragic accidents. Let’s look at Air Ontario flight 1363 (March 10, 1989) for instance. The aircraft in use was a Fokker F-28 with service from Thunder bay to Winnipeg with a stopover at Dryden. The flight had been delayed at Dryden due to deteriorating weather and to avoid further delays, the crew decided to just refuel and not to deice. When the aircraft was cleared to take-off, the take-off was slow/sluggish and the aircraft didn’t climb fast enough. 49 seconds later, the aircraft crash landed killing 21 of the 68 passengers and 3 (including both pilots) out of 4 crew members. A similar incident occurred in 1992 where another Fokker F-28, operated by USAir with service between New York and Cleveland (USAir Flight 405). The airplane was de-iced (twice actually!), but the crew were stuck in a ‘queue’ while taxing to the runway. When they did make it to the runway, the captain, in an effort to avoid further delays, decided not to go back to be de-iced and continued with the take-off. As fate would have it, there was an accumulation of thin ice (invisible from the cockpit) on the wings. The aircraft stalled just after lift-off and crashed, killing 27 people on board. To prevent such accidents from happening again, American and Canadian regulations (and I’m sure other countries that have snowy winters have these regulations too!) have prohibited take-off if the aircraft has not been de-iced.
How do they de-ice airplanes?
While taxing to the runway for take-off, the aircraft takes a detour to a ramp called the ‘de-icing facility’. A good analogy to understand the operation at the de-icing facility would be that of a queue at the gas station – as a fuel dispenser is ready for use, the first car heads to the dispenser and the other cars take a step forward. The de-icing facility have multiple bays where the aircraft can park and get de-iced. It gets very busy during winter as flights are delayed due to bad weather. When the weather clears, regular scheduled flights and the delayed flights rush to get de-iced and take-off to avoid further delays and furious passengers. To handle this, the de-icing facility have their own radio frequency and communicate with the pilots directly. As the bay opens up, they contact the pilot and ask them to proceed to the empty bay to get de-iced.
Check out this Just Planes video for a pilot’s eye view of the de-icing facility in Toronto (YYZ) – Link: Air Canada Winter Ops – opens in a new tab.
What’s in a spray?
First let’s get the technical terms out of the way. De-icing involves spraying fluids that removes the accumulated ice from the control surfaces (i.e., flaps, spoilers, elevators etc.). Anti-icing on the other hand, involves spraying fluids that prevent further buildup of ice. In aviation, the de-icing procedure typically involves spraying the de-icing fluid first and then the anti-icing fluid. The ‘Society of Automotive Engineers’ and the ‘International Organization for Standardization’ publishes standards for four types of fluids that are used in aviation as de-icing and/or anti-icing fluids. These fluids are made up of different combinations of glycol and water. Type I – This is a de-icing fluid that removes accumulated snow, ice and frost off the control surfaces. This fluid is dyed orange for easy recognition. Type II – This fluid is thicker than the Type I fluid and adhere to the wing until the aircraft travels at or above 100 knots. The Type II fluids are being phased out in favor of the Type IV liquid. Type II fluids are typically dyed yellow. Type III – This fluid is like an intermediate between Type I and Type II. They are pre-dominantly used on aircraft whose take-off speed is less than 100 knots. Type III fluids are dyed yellow too. Type IV – This an anti-icing fluid and provide a long holdover time. These fluids are dyed green. The main difference between the four types of fluids is the ‘holdover time’ – or the time from when the aircraft is de-iced to the time the aircraft is airborne. If the aircraft is delayed on the taxi way beyond the holdover time, then the aircraft has to go back to the de-icing facility for another de-icing session.
Interestingly, the formation of ice on the fuselage of an aircraft is not restricted to when the aircraft is on the ground. Lets take the cases of XL Airways flight 888T, Air Florida Flight 90 and more recently British Airways Flight 38 and Air France Flight 447. These accidents were all caused (at least in part) due to in-flight ice formation. The two primary causes of in-flight-icing are clouds and freezing temperatures. While freezing temperatures speaks for itself, clouds are a visible mass of super-cooled water droplets. When an aircraft passes through a cloud, the droplets that come in contact with the aircraft freezes instantly. Modern jet airplanes are equipped with heated windscreens, instruments, intakes and probes to handle such temperatures. Furthermore, the aircraft’s wings are kept warm because the leading edge (the part of the wings that are visible when you face the aircraft head-on) are warmed by hot air bled from the engines. Turboprops (like the ATR series or the Dash Q400) have electric heaters to deice their propellers. One other feature that’s unique to propeller airplanes is the ‘boot’. The boot is a rubber cover that is usually found over the leading edge of the wing and the elevators. During icy conditions (in-flight), the boot expands and breaks off any ice that adheres to the aircraft.
Well the next time you fly during the winter break, I hope you don’t lose your cool if your aircraft takes a detour to the de-icing facility…after all it’s for your safety. I hope you enjoyed this article and as always comments, suggestions and questions are welcome! Until my next post….Happy Landings!!!