European Winter Aviation

“A layer of ice on the aircraft is especially dangerous during takeoff,” warns Horst Apel, who is in charge of de-icing work at the Lufthansa base in Frankfurt. The lift required to get a plane off the ground is blunted when the air is unable to flow over smooth surfaces. Ice and frozen snow roughen the aircraft skin and make it uneven; they alter the aerofoil, add weight and make takeoff a risky exercise.

To eliminate the hazard, about 340 specially trained Lufthansa ground staff are assigned to winter duty at Frankfurt airport. Besides servicing Lufthansa jets, they also de-ice the aircraft of most other airlines operating flights from Frankfurt.

In an average winter, the Frankfurt maintenance men use up a million litres of de-icing fluid supplied by twelve tankers. Removing the ice from smaller short to medium-haul airlines normally takes between 150 and 200 litres of the fluid consisting of a glycolwater mixture. Wide-bodied aircraft like the Boeing 747 require 400 to 500 litres; and if snow is falling, this can rise to between 1,500 and 2,000 litres. Consumption reached a record peak at Frankfurt airport on November 21, 1985, when planes preparing for takeoff were sprayed with about 170,000 litres of the special fluid which fortunately is bio-degradable and poses no threat to ground water.

One of the basic rules of Lufthansa de-icers is always to do the job hot. “The fluid should be heated to a temperature of 80° to 85°C,” says Horst Apel. The standard mix, consisting half and half of water and glycol, prevents the formation of ice crystals down to temperatures of minus 30°. “When the temperature dips below that, we increase the dosage of glycol. ” The fluid, from Hoechst AG or an English supplier, costs about $A2. 80 per litre. The water is added by the Lufthansa specialists themselves. And to make doubly sure the mixture is spot on, they take random samples from every tanker every time they are refilled.

Deicing is done both in the hangar and outside. It is done mostly on the tarmac when time is short: for example, if a plane is at Frankfurt on a brief stopover or if the captain, who is responsible for the aircraft, decides shortly before takeoff that his plane needs to be de-iced. In the open, the men normally spray a ready mixed solution over the plane. But “if we work inside the hangar, we do what we call two-step de-icing,” explains Horst Apel: the aircraft is first de-iced with hot water and then sprayed with the special fluid. This may take more time but it reduces consumption of the expensive glycol solution.

After de-icing, the major problem is to ensure it lasts long enough to get the plane safely aloft. If it is only frosty, the treatment will keep the aircraft ice-free for up to eight hours but if it’s snowing – at most an hour. Sleet is even worse than snow. Once de-icing is completed, the pilot has to takeoff as quickly as possible since in the worst of weather, the de-freezer will last for only 15 minutes. As Horst Apel puts it succinctly: “The difficulties we face in our work depend essentially on two factors: how cold it is and how wet. ” As bad weather also increases the incidence of peak hour traffic delays then often the system becomes saturated as aircraft holding on the ground become ice-affected prior to receiving a takeoff clearance.

Once the aircraft is in the air, frost is virtually powerless against the plane’s own mid-air heating system. A sophisticated network of pipes feeds hot air to all the critical points on the aircraft surface, especially the leading edges of the wings. The system draws its heat from the engines. The front window of the cockpit is heated like the rear window of a car to keep vision clear. This way, jet airliners defy temperatures as low as minus 60°.

Fortunately, snow and ice pose problems to aircraft only on the ground. From November 1 each year, the tanks of the spraying vehicles are filled with ADF and the de-icing teams and their equipment are on stand-by to ensure that Lufthansa and other airline flights takeoff safely even in the depth of winter.