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Why pilots need to understand the weather

by Captain Chris Hammond Retired Captain and BALPA Member

As World Meteorological Day (23rd March) approaches, I thought I’d reflect on just how much a pilot’s life revolves around the weather.

Flying around the globe means pilots traverse all sorts of climates and come face to face with all manner of weather. We spend our time up in the clouds amongst the weather, and what it’s doing determines every aspect of out flight.

As such an understanding of meteorology is vital to the decisions we make. Over the years at the controls I routinely had to allow for strong winds, consider how icing would affect the flight, vector around thunderstorms and even avoid hurricanes.

In fact, pilots are required to study meteorology practical and theory to a high level and need to pass exams to test their knowledge in both before being granted a commercial or Air Transport Pilot’s Licence (ATPL). The areas covered include local and worldwide weather patterns, such as winds, cloud formation, met phenomenon (hurricanes, squalls, thunderstorms, tornados, water spouts etc) and the effect of these on aircraft. Pilots are also taught about the jet streams location and trends as well as the ITCZ (inter-tropical convergence zone) and their effect on aircraft and worldwide weather.

From the moment a pilot even begins to plan a flight, finding out what weather they may experience en route and at the destination is incredibly important. Aircraft behave differently depending on the weather, for example air temperature and wind speed both affect aircraft performance. So, before and during a flight, pilots will keep informed about any weather that could affect their planned route. We may need to alter our plans to avoid weather that could be detrimental. Here are some examples…


Thunderstorms don’t just cause turbulence and make the flight uncomfortable, they can cause an increase swiftly followed by a decrease in performance, which could actually be outside the capabilities of the aircraft.

Temperatures and pressure:

Aeroplanes are designed to be operated within a range of temperatures from very cold to very hot and pilots are rigorously trained to handle the variations. But temperature does affect performance and pilots have to be aware of this. One problem associated with heat is that as air gets hot it becomes less dense meaning it gives less lift and less engine performance.

Very cold temperatures, or very low atmospheric pressure will mean that the heights read from the instruments will be significantly higher than you actually are so will need to be converted to account for that, if both low pressure and low temperature are encountered, this could be thousands of feet, so could spell disaster if not adjusted by the pilot.

Snow and ice:

The manuals, information and procedures required for cold weather operations are vast. Pilots undertake lengthy training that includes gaining an understanding of how to deal with adverse conditions and how to assess whether it is safe to take-off or land in poor weather.

Icing, and how and when it can occur, is another huge consideration for pilots, avoided if possible and always taken into consideration. Different types of icing and the significance of each are vital, as some can accumulate rapidly and cause enormous problems to aircraft.

Most commercial aircraft are equipped with weather radar, some with storm scopes to show electrical activity in thunderstorms, as well as anti-icing (preventative) and de-icing (removal one ice is formed), but how and when best to use them is down to pilot training and knowledge.


Strong winds are a major factor in flying an aeroplane safely and need to be considered at all times, particularly during take-off and landing. Pilots need to understand how the local topography, such as mountains, can affect winds and cause a massive difference depending where you are in relation to it and the wind strength and direction. Some airports, such as Gibraltar, are known for particularly tricky downdrafts and winds.

Some particular cases:

There are some places known for their own particular weather that can make flying tricky. A phenomenon called foehn winds mean one side of a mountain range has different weather to the other side – the mistral down the Rhône valley is an example that makes flying difficult… flying through the Andes is better than flying over them in some conditions because of ‘standing waves’ and destructive turbulence. As mentioned earlier, cross winds and down drafts from the rock of Gibraltar are known to make landing there tricky.

Pilots also must be aware of how much fuel to take to allow for changes in weather. Pilots are taught to look out for particular types of weather fronts over north east USA which could mean you will need more fuel if you are heading to places like Chicago or Toronto.

While no pilot can look in a crystal ball and know for certain what the weather will bring, it is important that they understand the trends and can predict what is likely to occur. Without good forecast and updates on what the weather is doing at the time of a flight pilots wouldn’t be able to do their job. In fact, in many ways a pilots’ working life is hugely dependant on what the weather brings.