Halloween 1994. American Eagle Flight 4184 is en route to Chicago from Indianapolis, but bad weather in the Windy City is causing delays. Air traffic control decides to hold the plane over the nearby LUCIT intersection at 10,000ft. While holding, the plane encounters freezing rain. An intense build-up of ice rapidly ensues, leading the commuter vehicle to lose control and crash into a soybean field near Roselawn, Indiana. All 64 passengers and four crew members are killed.

Flight 4184’s devastating demise might be the best-known example of a fatal aircraft event caused by wintry conditions, but it is not the only one. In fact, ice is believed to factor in as many as 10% of fatal crashes.

Problems occur when small cloud droplets freeze on the vehicle’s wings; the resulting crystals reshape the surface and change the structure’s aerodynamics. Drag is increased and reduces the lift needed to keep the plane in the air.

"If you have a very small amount of roughness on a wing, the air will not flow linearly, it will flow in a turbulent way," explains SAE International’s Dr Jacques Leroux. "If the plane will not lift, or there was unequal lift on both wings, it could literally go belly up."

A chemist at Dow Chemical Canada, Leroux was involved in the development of anti-icing fluids before attracting interest from SAE, whose main purpose is to collect, develop and disseminate technical information related to mobility technology. He’s now the chairman of its G-12 Ground De-icing Committee and co-chair of the organisation’s Aircraft De/Anti-Icing Fluids Subcommittee. Leroux has also been awarded the Henry Souther Standards Award for his accomplishments in standards development in the field.

"There could be 60 or 70 different airlines, and every airline was trying to come to the station and say: ‘you have to use our procedure, because that’s the one approved by our regulator’."

He explains that ice on the runway is generally removed using salt, but because the compound is corrosive, it’s not suitable for aircraft use. Most companies therefore deploy a heated mixture of water and propylene glycol on a plane’s wings. These fluids have a low freezing point, and the ability to melt ice and snow on application.

"When you apply the heated fluid, it melts the snow and what’s left on the wing is a liquid with a low freezing point that will not refreeze," he says.

In particularly extreme conditions, and after the snow and ice are removed, anti-icing fluids are applied. These viscous liquids are able to protect the aircraft for longer than the initial glycol solution against frozen precipitation.

Finite possibilities

Such procedures are vital to an airline’s repertoire. When an organisation wants to fly where there are icy climbs, it has to file with a regulator of winter operations for de-icing procedure approval.

"Generally, regulators do not issue a standard measure," Leroux explains. "What they do is approve the methods that are generated by various airlines."

Each airline having an individual de-icing procedure was once not particularly troublesome. There are, after all, a finite number of ways to complete the task. But it’s becoming more of a problem with the increasing incidence of hub airports.

"It’s really because more and more airlines will rely on third parties to do the de-icing, particularly at very large airports," says Leroux. "People used to fly from one point to another, but nowadays, many are flying to hub airports and travelling from there to the final destination."

To increase efficiency, centralised de-icing facilities (CDFs) have started operating in many countries. In some instances, over 80 airlines fly into such a complex, each attempting to impose its own standard for de-icing on the staff there.

"For an airport like Toronto, there could be 60 or 70 different airlines, and every airline was trying to come to the station and say: ‘you have to use our procedure, because that’s the one approved by our regulator’," says Leroux.

That’s a pretty big ask; staff would have to be trained for each procedure, resulting in a multitude of methods, high training costs and an increased risk of non-compliance.

The centralised stations initially responded to this worry by agreeing to use just one method, approved by a local regulator – Transport Canada, in Toronto’s case. But as the number of facilities increased, so too did the various ways of de-icing.

"Every centralised facility has a slightly different process, in addition to the method of each airline and the various third parties that do the de-icing," says Leroux. "It had become apparent that, as time goes by, it’s important to have more standard procedures."

Standard crafting

Airlines were starting to realise that in order to be safer while also reducing costs, de-icing was to be viewed not as a competitive process – where one company strives to do it faster and better than the next – but as a collaborative effort.

"In order to be safer while also reducing costs, de-icing was to be viewed not as a competitive process – where one company strives to do it faster and better than the next – but as a collaborative effort."

In May 2009, the International Air Transport Association (IATA) approached the SAE to work towards a globally harmonised de-icing procedure. The two organisations agreed to enter into a formal cooperation agreement and became sponsors of the newly created Council for Globalised Aircraft De-icing Standards. At its first meeting in Montreal in November 2011, the International Civil Aviation Organisation (ICAO) became an additional team member.

"We picked the methods document, a training document and an audit document that would be in scope of the standards we would rewrite," Leroux says.

Involved in the task are volunteers from all over the globe. Together, they look at existing procedures and work out the best way of crafting them into a single instructions sheet that can be used by airlines worldwide.

Leroux admits it’s a time-consuming process but certainly a worthwhile one, and the team have made good progress so far. He hopes there will be a first version of the methods paper ready for balloting sometime this year. The team are also already working on the training and quality control documents. Once the methods paper is released, Leroux believes the process for the remaining two will accelerate rapidly.

Surprisingly for an international operation, there haven’t been too many problems to contend with, and incidents such as that suffered by Flight 4184 are likely never far from the consultancy’s mind.

"It’s actually going very well right now," says Leroux. "People are always very enthusiastic, optimistic and think these things can be done very quickly. But they can’t, because the people who work on this do not work on it full time. But I wouldn’t say we have had any particular key difficulties.

"It makes a change. I think people realised that this is an important safety item. And the only way you can improve safety is through putting the best minds together and working on it."