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AIR SAR

Understanding the dangers of aircraft icing

Freezing rain makes for slick roads and terrible driving conditions, but what happens when you combine freezing precipitation and flying?

It leads to serious problems that Environment Canada's Meteorological Service of Canada (MSC) spent four months researching.

From November 2003 until February 2004, the MSC was one of the agencies leading a major North American study to better understand aircraft icing and hazardous winter weather.

Aircraft icing forms when airplanes encounter freezing precipitation or cloud droplets with temperatures colder than 0°C. Ice can attach to the wings, tail and windshield, making flying dangerous.

Icing has led to an average of 30 deaths and 14 injuries in the United States each year. Statistics for Canada show an average of 50 fatalities each year.

Five research planes
The $3 million study, with partial funding from the New SAR Initiatives Fund, was conducted near Montreal's Mirabel airport because of the high occurrence of freezing precipitation - approximately 50-75 hours each year - and because this area around the Great Lakes is a high air traffic region. Within North America, only Newfoundland and Labrador has more hours of precipitation, with 150 hours a year.

The study had five research planes set to take off from Ottawa, Ontario; Cleveland, Ohio; and Bangor, Maine during storm conditions to collect storm data from different heights in the atmosphere on flights to Montreal.

The study made use of data collected in-flight as well as on the ground. This information will help researchers better understand weather formations, including places where freezing precipitation is more common, and the reasons for this.

Ice accumulation
Dr. George Isaac, Senior Cloud Physics Research Scientist with the MSC, gave a presentation on aircraft icing at the SARSCENE 2003 workshop. He talked about the importance of this study and said the majority of accidents occur in private and not commercial aviation.

Even a small amount of ice can decrease fuel efficiency and affect a pilot's ability to fly an aircraft as illustrated by this windshield wiper.

Aircraft icing is a major problem, but accidents are not necessarily caused by ice accumulation. Even a small amount of ice, he said, can decrease fuel efficiency and affect the pilot's ability to manoeuvre an aircraft, and pilots must be aware of their aircraft's certification for flying in icing conditions.

Further, Dr. Isaac stressed the need to improve current icing forecasts. Because of the difficulty of producing such forecasts, they have been traditionally conservative, forecasting a potential hazard over a larger than necessary region. Significant improvements have been made in the numerical weather forecast models to help solve this problem.

Ultimately, this study will improve air travel safety through better forecasts and detection of winter weather hazards.

Other Canadian partners in the study include Transport Canada, Department of National Defence, Communications Research Centre, McGill University and Trent University. Major American partners include the National Oceanographic and Atmospheric Association, National Science Foundation and the Federal Aviation Administration.

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