Why it's so critical to deice planes prior to takeoff

By Ashley Williams, AccuWeather staff writer

During the chilly winter months in which snowy and icy conditions are common in colder climates, air travelers may notice ice accumulation being blown off their aircraft while they patiently wait on board for takeoff.

It’s an essential process in aircraft safety, as ice buildup can hinder a plane’s ability to fly smoothly and safely.

“Snow, ice and frost change the shape of the wing and tail and their ability to generate lift – the force that allows an airplane to fly – and increase weight and drag – the forces an airplane must overcome in order to fly,” said William Herp, a pilot and the CEO of regional air charter online marketplace Linear Airline Taxi.

Therefore, it’s critical that these contaminants be removed prior to takeoff, Herp said.

Plane being deiced - AP Image

A plane is deiced on a snowy Presidents Day at Washington's Ronald Reagan National Airport Monday, Feb. 15, 2016. . (AP Photo/Andrew Harnik)

The presence of ice alters the smooth airflow over the wings, according to Brett Manders, international airline pilot and author of the book, “Behind the Flight Deck Door.”

“Smooth airflow assists in the production of lift, and if ice accumulates on the wings, it distorts the smooth, laminar flow of air over the wing, and lift is reduced,” Manders told AccuWeather. “If lift is reduced too much, there's the potential of an aerodynamic stall.”

Ice can accumulate on every exposed frontal surface of an airplane, including on the wings, propeller, windshield, antennas and vents, according to the Aircraft Owners and Pilots Association’s Air Safety Foundation.

Enough ice buildup can cause the engine to stop working. “In moderate to severe conditions, a light aircraft can become so iced up that continued flight is impossible,” the Foundation noted.

Ice on the wings and tail of an airliner can be fatal. In March 1992, USAir Flight 405 crashed shortly after takeoff near New York’s LaGuardia Airport, partially due to improper deicing procedures and large amounts of ice accumulating on the wings and airframe.

How planes are deiced

“If an aircraft has been parked for a while, say overnight, and ice has formed, it will need to be deiced,” said Manders, who added that in the presence of conditions like snow or freezing fog, the aircraft will have to be anti-iced.

Planes will have anti-ice equipment on the wings and engines, Manders said. These systems use electrics or hot air from the engines to heat up the leading-edge surfaces. “This [lets] the ice melt and fall off, or prevents its formation altogether,” he said.

Both procedures involve the use of heated liquids, according to Manders. “However, the anti-ice solution has certain chemical properties to prevent the formation of ice for a given period,” he said. “This period of time is called ‘holdover time,’ and the aircraft must take off before this time has expired.”

Once everyone is on board, a plane will typically move from the gate to a special deicing area to begin the multi-step process. “The area serves two purposes: to collect runoff of deicing fluids in order to protect the environment, and to position the aircraft closer to the runway to minimize exposure to new accumulation if it's still precipitating,” Herp said.

First, a heated glycol-based solution, which is usually an easily identifiable orange color, is applied to remove any accumulated snow or ice from the aircraft. Glycol has a lower freezing point than water, and is commonly used in antifreeze, according to Herp.

“If it is actively precipitating and the aircraft requires continued protection prior to takeoff, then a second gel-like anti-icing fluid that is usually green in color is applied,” he said.

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The gel-like nature of the substance gives pilots time to taxi to the runway and finish their final safety checks, and it’s designed to slough off as the aircraft gains speed upon takeoff so that it won’t affect the shape of the wing and tail.

“Often, the pilots will shut down the engines during the deicing process so the fluid doesn’t get dispersed through the engines, and they also close vents to keep the fluid from entering the cabin, although sometimes odors will find their way in,” Herp said.

Once a plane is airborne, its forward speed through the air keeps any frozen precipitation from accumulating on surfaces other than the leading edges of the wing, tail and engine inlets. These areas are protected during flight by anti-icing equipment on the airplane itself, according to Herp.

“On a typical airliner, the silver panels on the leading edges of the wings and tail and around the engine inlets are heated by hot air from the engines, and are very effective at eliminating ice buildup in flight,” Herp said, adding that there are also heating elements inside the plane’s instruments that collect outside air information used to operate the aircraft.

“[Over the years], technology like weather [information] in the cockpit, improved forecast tools and procedural changes in flight operations have helped air carriers avoid and better manage flight in icing conditions,” Herp said.

For more safety and preparedness tips, visit AccuWeather.com/Ready.

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