Why Hot Weather Can Prevent Airplanes from Taking Off?
Extreme weather can have a direct impact on an aircraft's performance.
In cold weather, ice can build up on the wings and control surfaces, reducing aerodynamic efficiency. In hot weather, the air becomes less dense, so an aircraft must reach a higher speed to generate enough lift for takeoff. In simple terms, the hotter the air, the more difficult it is for an airplane to take off.
In some cases, extreme heat can even make takeoff impossible. In June 2017, for example, temperatures in Phoenix, Arizona reached 49°C (120°F), forcing more than 40 flights to be canceled.
Why Does Hot Weather Affect Takeoff?
The answer lies in a concept called density altitude.
As the temperature rises, the air expands and becomes less dense. Even though an airport's elevation does not change, the aircraft performs as if it were taking off from a much higher airport, where the air is naturally thinner. For example, an airport at sea level on a 45°C day may perform like an airport at an elevation of about 2,000 meters (6,600 feet).
Thin air affects an aircraft in two major ways:
Less lift: Wings create lift by moving through air. When the air is thinner, they produce less lift.
Less engine thrust: Jet engines need large amounts of air to burn fuel efficiently. Hot, thin air contains less oxygen, so the engines generate less thrust.
With less lift and less engine thrust, the aircraft needs more runway to accelerate to takeoff speed. If the runway is not long enough, it may not be able to take off safely.
Is There a Temperature Limit for Takeoff?
There is no fixed temperature at which airplanes can no longer take off.
Whether an aircraft can depart depends on several factors, including the aircraft model, its weight, and airport conditions such as elevation, runway length, runway slope, and wind. Because these conditions vary from one airport and even one runway to another, the temperature limit is different in every situation.
For example, under the same operating conditions, an Airbus A319 taking off from Runway 08 at Paris Orly Airport (ORY) with no wind has the following Regulatory Takeoff Weight (RTOW) limits:
4°C: about 74.4 tonnes
24°C: about 73.6 tonnes
44°C: about 72.7 tonnes
As the temperature rises, the maximum allowable takeoff weight decreases because the aircraft needs more runway to get airborne. To stay within safety limits, airlines may have to reduce the aircraft's weight by carrying less cargo or limiting the number of passengers.
On some long-haul flights, hot weather may also limit how much fuel the aircraft can carry, making a technical refueling stop necessary. In regions with extremely high temperatures, such as the Middle East or the deserts of the United States, airlines often schedule long-haul departures late at night or early in the morning, when cooler temperatures and denser air allow aircraft to take off with a heavier load.
