Too hot to fly? The effects of heatwaves on air travel

How does heat affect airplanes?

Planes are inherently heavy, and to become airborne, they must overcome the force of gravity, which keeps them on the ground. To do this, they must generate lift. 

One of the ways they do this is explained through Bernoulli’s theorem.

Airplane wings are designed with a special shape called an airfoil. The top surface of the airfoil is curved, while the bottom surface is flatter. This shape causes the air to move faster over the top of the wing and slower underneath.

According to Bernoulli's principle, faster-moving air has lower pressure, and slower-moving air has higher pressure. This pressure difference creates an upward force, or lift, on the wing.

This is not the complete explanation for lift, as it leaves a number of big questions unanswered. However, it has been demonstrated to form a large part of the explanation.

We also know that lift also depends on multiple factors, such as the speed and density of the air. When the density of air is higher, as in cooler or lower-altitude conditions, there are more air molecules available to create the pressure needed for lift. But during heatwaves, the air molecules are excited; they move faster and are farther apart from each other, which makes the air thinner and, as a result, there is a decrease in lift.

Airplanes can only take off when the force of lift overcomes their own weight. Engines make this possible by providing the necessary thrust to move the airplane forward and also to achieve the speed required for generating lift. This is enough to get the average airplane airborne, even in relatively high heat.

But in extreme heat, such as has been seen in many regions this summer, air is less dense, meaning there is a reduced amount of oxygen available for efficient fuel combustion within the engines. Consequently, the engine may have performance issues that can also impact the airplane’s ability to take off and fly safely.

Too hot to fly?

Generally, aircraft may experience some performance issues above 86ºF (30ºC). More specifically, this depends on the type of aircraft. For example, a Boeing 737 can operate at a maximum air temperature of 125.6ºF (52ºC), and an Airbus A320 can operate at a maximum air temperature of 122ºF (50ºC), according to the manufacturer’s specifications.

Whether a plane can fly or not doesn’t only rely on air temperature, though. Another factor to take into account is the length of the runway. As we’ve stated above, in hotter weather, aircraft engines and wings may work less efficiently, and airplanes may require more lift than usual to take off. 

Thus, some runways may not be long enough to allow aircraft to achieve the necessary speed (and lift) to take off, especially at higher altitudes, where the air is already less dense. In areas where hot weather is the norm (such as in the Middle East), airports are built with longer runways for this reason. 

Then, there’s the problem of weight. If all the seats of an airplane are filled, and there is extreme heat, the engines must work a lot harder to move the aircraft, which might lead to engine overheating. This is why some airlines apply weight restrictions on summer flights. For example, in 2018, British Airways had to bump 20 passengers off a flight from London to Ibiza when the temperature reached 95ºF (35ºC). 

This has also happened more recently, in 2023. Most airlines, however, prefer to find passengers who agree to be put on another flight, rather than bump them, as the monetary compensation for the passengers is usually lower than the regulatory fines related to denying boarding involuntarily.

Environmental impact 

In other cases, airlines may opt to transport bags on a different flight or reduce the airplane's fuel load. In this case, aviation authorities may plan additional stopovers to refuel. One side effect of this is that the additional take-offs and landings tend to increase the amount of carbon dioxide (CO2) emissions from air travel.

Moreover, as engine performance is reduced by hot weather, airplanes also need to consume more fuel to cover the extended travel times. This extra fuel consumption, in turn, leads to higher carbon emissions, contributing to global warming and environmental degradation.

Economic implications

As you can imagine, all of these difficulties related to extreme heat have economic implications for airlines and create inconveniences for passengers.

If an airplane needs a longer runway to take off due to the heat affecting its engine performance, the flight must be redirected to another airport with a longer runway. Some flights may have to be rescheduled for the night-time when the temperatures are lower. 

Overall, there is a high risk of delays, cancelations, and rescheduling, increasing costs associated with additional crew hours and passenger compensation.

Operating costs may also be increased as planes with reduced engine performance tend to consume more fuel. Airlines may need to budget for more fuel for the same routes or modify their flight plans to optimize fuel efficiency. 

Extreme heat can also affect aircraft systems and components. Because air conditioning and engine cooling systems tend to work harder in hot weather, they require more maintenance and repairs than in other seasons. These may all see like relatively small effects, but added together then can add a good deal of additional cost. This can have an outsize effect because airlines often work on very low margins.

How will we deal with this?

In the Middle East, airlines are already trying to minimize heat-related disruptions by scheduling more flights in the early morning and late evening.

More permanent solutions for the heat problem in the aviation industry include extending runways in the airports that are most affected by heatwaves, and manufacturing aircraft using lighter weight materials (such as carbon fiber) and improved aerodynamics, particularly in the wing design. This would optimize lift generation, even in hot weather.

In the meantime, rescheduling flights for cooler hours and reducing the number of passengers, bags, or fuel are the most feasible options —with all of what that implies, both economically and environmentally.