Thunder, fog, blizzard and wind are difficult weather conditions challenge flying. Tapio Siivola and Karri Hannula discuss how weather conditions affect their work.
1. Thunder – a summer nuisance
“An aircraft will start descending for landing 10–15 kilometres from the runway, and if there is a thunder cloud on the line of approach, the runway in question may be unserviceable. The same problem exists with takeoff. You can’t fly through or underneath a thunderstorm cell because of the risk of convection currents and hail. Sometimes you need to go to great lengths to fly around them. It’s easy to see thunder clouds during the day, but at night, you can only detect them with the weather radar,” says Siivola.
“The conditions change quickly during a thunderstorm. Wind direction may turn 360 degrees within half an hour. Consequently, thunder restricts the number of planes departing from and arriving at the airport. A thunder cell close to the airport with lots of lightning may prevent the fuelling, loading or unloading of planes,” explains Hannula.
2. Fog may prevent landing
“If the weather is foggy, the distances between approaching planes must be kept longer, and planes may have to circle the airport before landing. If you can’t detect the runway from 30 metres when landing, you may have to pull back up and try again or head to another airport. The objective is a safe landing,” Siivola continues.
“In dense fog we apply low-visibility methods, which means increasing the distances between planes in the air and on the ground, decreasing the speed of vehicles and pausing work on the apron. If you have 36 planes landing per hour on each runway in normal conditions, then foggy conditions reduce their number to 24 planes per hour,” says Hannula.
3. A blizzard makes runways slippery
According to Siivola, snowfall is a challenge especially if there’s also a strong wind.
“We always try to land headwind because crosswind makes landing difficult. Crosswind conditions can be good enough in summer, but during a blizzard, the slippery runway sets limits to landing, and we may not be able to land at all. We always determine an alternate aerodrome with a good weather forecast prior to take-off,” he says.
4. Ice and humidity are a tough combination
Even if there is no snow, icy conditions can challenge airport operations.
For one, aircraft engines have to be de-iced, and the runways cleared of ice to ensure safety. De-icing capacity is in full use. Finnish airports’ specialty is the amount of de-icing capacity available. Thousands of aircraft are cleared of snow and ice every year, and especially Helsinki Airport’s de-icing equipment is top notch.
“The worst situation is frost with a lot of humidity in the air, as that will freeze the aircraft engines. This means that the aircraft cannot taxi themselves to the de-icing station, but the de-icing vehicle has to drive to each aircraft separately,” says Siivola.
5. Gusts complicate flying
“If the wind is strong but steady, it doesn’t really bother flying. On the other hand, a gusty wind that changes direction at a fast pace is a real challenge. Rapid changes in wind speed during landing may lead to a missed approach and try again a bit later – or head to an alternate aerodrome. The wind can be very strong in Norway and the British Isles, for example,” Siivola says.
“At Helsinki Airport, if the wind is strong, it may render the main runway unusable. Such conditions will force us to resort to other runways, which limits the number of planes landing and taking off and causes delays in air traffic,” Hannula shares.
The article was first published on September 13th, 2018.