Ice-clad runways and safe landings

If cars were made for roads and planes for air, could aerodynamics explain why planes might skid when the runway is clad in a blanket of ice?

Driving a car is not rocket science and, for that matter, even piloting a flight isn’t. It is a learned skill; one that is structured by rules and regulations to ensure safety. But with weather acting as a yardstick for every kind of motion – land, water or air, there is no doubt that one needs to be specially trained to handle such machines in extreme conditions.

For example, a car driving on icy roads takes as much as ten times longer to halt, in comparison to the regular black-top road. Although this means staying a minimum of 20 seconds behind the car in front, driving on iced roads is not just about maintaining the distance; it is about employing a different style altogether. It brings to fore all the controls, as the chances of losing grip on icy roads are high. It also brings up the time tested slow-and-steady quotient to tame the road for the drive.

Seen in that perspective, perhaps an analogy could be drawn between a car on the road and an aircraft taxiing a runway – as far as the visual reference is concerned, that is. Just like cars require additional road space to regain control on an icy road, so do airplanes; longer the runway, better the recovery time. But aerodynamics is a dynamic subject, both literally as well as figuratively. While cars can be brought under control by following the rules of icy roads, pilots have a list of do’s and don’ts to follow when runways turn into an ice rink.

Can a flight land on ice-clad runways?

The answer to that question is a simple yes. Although ice formation can affect the aerodynamics of the aircraft, its anti-skid system or the anti-lock braking system (ABS) can prevent the main landing gear wheels from locking up during landing on icy runways. But yes, snow and ice, could, sometimes (read that as rarely), cause planes to skid off the runway, as frost/snow covered runways can become very slippery. The prospect, however, changes when the runways are completely clad in ice; they provide greater friction, enabling airports to operate without interference.

So, how exactly does the process of landing happen?

Like your everyday car, braking is the key to stop even in an aircraft. Airports track the ‘braking action’ condition of the runway and, if it is less than ‘good to medium’, the same is conveyed to the pilot. A point to note here: in the world of aviation, runways are categorized as good, good to medium, medium, medium to poor, poor and nil. What happens when the brakes are applied is that the tire rolls slower than its regular free rolling speed, resulting in ‘slip’. Maximum braking friction is generated when ‘slip’ is around 10 percent lesser than the synchronized speed.

Yes, it is for the airport authority to maintain the runways and communicate the condition to the pilot, however, the ultimate decision to land is in the hands of the pilot. If the pilot feels he/she is jeopardizing the lives of his/her passengers, he could abort the landing and opt for another airport. The chances of that happening may be less, considering the careful planning and implementation of every flight, particularly in destinations where weather conditions are extreme.

A quick check of runway excursions statistics is proof enough to assure passengers to wintry destinations that they are safe. According to the International Air Transport Association (IATA) ‘Runway Safety Accident Analysis Report 2010-2014’, of the total of 415 accidents worldwide, only 90 were classified as runway/taxiway excursions