How does a plane land in snow? What problems can heavy wind cause? How does a pilot land when thick fog reduces visibility? A pilot gives some insight into how poor weather affects flights.

Although the heavy snow forecast for today (12th January) has forced Heathrow to cancel dozens of flights, the airport handles hundreds each day, so there will still be plenty of aircraft taking off and landing despite the wintry conditions. We asked former airline pilot and flight safety specialist at the British Airline Pilots’ Association, Steve Landells, to explain how pilots do their job in poor weather.

Snow and ice

“In aviation, we all strive to make sure that every situation and eventuality is accounted for – we don’t like surprises. There is, however, one issue over which we have no control; the weather. Pilots will be well trained in assessing whether it is safe to land in poor conditions; if not, they might choose to divert to another airport.

“While heavy snow can decrease visibility, a big concern is the snow or ice on the runways. Airports will work hard to plough snow and de-ice the runways to allow aircraft to continue to come and go safely. Taking off and landing on ‘contaminated’ runways requires the pilot to take note of weather reports and the condition of the runway surface in order to carry out complicated calculations, which will determine the aircraft’s performance.

“Because the runways need to be vacant while being cleared and the aircraft also de-iced, flights can’t take off or land during this time, which is what leads to delays and cancellations as airports decide to reduce the total number of flights that day.”

Wind

“Aircraft are significantly affected by wind because not only do they have a large surface area, but they also have a huge fin at the back that wants to act like a weather vane and cock the aircraft into wind.

“The pilots will work out what control inputs they might need during the take-off run. The crosswind will try to lift one wing and will try and turn the aircraft away from the runway heading, both of which need to be avoided. Typically, this will be done using rudder input to keep straight and aileron to stop any roll, which will be gradually reduced during the initial climb.

“Landing can be more of a challenge and a perfect landing in windy conditions is a very satisfying achievement for any pilot. Autopilots often can’t cope with strong crosswinds so manual landings in strong winds are the norm. There are a couple of techniques that may be employed, depending on aircraft type, but the aim is to stop the wind blowing the aircraft off the runway centreline.”

Fog

“Most large airports and modern aircraft are equipped, and pilots trained, so that landings in fog are possible. Before commencing an approach, pilots have to ensure that all the primary systems are functioning properly as well as the multiple back-up systems. Once the aircraft is set up, with the autopilot engaged, the initial approach is commenced.

“This process is largely the same as any other approach with the pilots controlling the height and direction that the aircraft is travelling in. However, this is all happening without visual reference to the outside world and the pilots are always ready to take control if anything doesn’t look right inside the cockpit.

“In modern aircraft, it is extremely rare for the systems to fail and as a passenger you may not notice the difference between an automatic landing and a manual one but for me it didn’t matter how often I did it, sitting there watching the aircraft land itself, with my hands hovering over the controls, instead of doing it myself was always a slightly peculiar experience.

“It’s not over once the aircraft is on the ground. You will still be travelling at over 100mph so the pilots have to slow the aircraft down and then they have the difficult task of locating the taxiway and finding their way to the terminal building.”