Snow is falling as you land. Looking out the window you see the airport as a “winter wonderland.” Your airplane slowly taxis to the gate for an on-time arrival. Your pilots have successfully flown into inclement weather safely.
What preparations went into that flight?
Winter weather can be challenging for every part of flight operations, starting with the airplane, which has to have very effective braking systems with anti-skid. The jets have reverse thrust and panels on the wing to kill lift, transferring the weight to the wheels for braking. Every modern jet airliner has to demonstrate the ability to safely stop on a runway that is contaminated with snow, ice or rain during certification. These demonstrations provide pilots with the landing distance needed to safely stop in adverse winter weather.
Pilots know that when landing on contaminated runways, a firm touchdown is needed to ensure that the wheels spin up properly, allowing the anti-skid system to provide the best braking. Another consideration is crosswind; because of the slippery surface only a limited crosswind is allowed. Pilots take all of these things into consideration before descending from cruise altitude.
Takeoffs in winter conditions bring challenges too. When precipitation (snow, sleet, ice pellets, freezing rain or drizzle) is falling, special procedures must be followed to have the wings and tail free of contamination before beginning takeoff. Contamination can distort airflow, causing a loss of lift and control.
De-icing the airplane is essential. Once boarding is complete, the captain taxis to a de-icing station where trucks with specially trained ground service personnel spray hot glycol onto the wings and other critical surfaces to melt any ice that is adhering. Once all the ice is melted, a special fluid is applied that prevents ice from sticking to the wing for a specific amount of time depending on the conditions. The airplane needs to be airborne before this time expires or return for de-icing again. Pilots carefully calculate this time, coordinate with air traffic control and plan the taxi time to the runway not to exceed this time, known as holdover time.
When flying in snow and ice, airliners have de-icing systems to prevent ice from building up on the wing and distorting the airflow. Most jets use hot air from the engine compressors to keep the leading edges of the wing heated. Engine inlets are also heated by engine compressor air, preventing ice from changing airflow into the engine. Windshields are electrically heated, as are airspeed probes. Airplanes must have special certification to fly in icing conditions.
Winter ops are challenging, but with modern airplanes and well-trained and experienced pilots and ground staff, we fly safely in these conditions every winter.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.