Why heat waves are grounding planes

FLIGHTSFROM PUBLISHED: 2020-01-21

Can it ever be to hot to fly? The answer is yes. FlightsFrom.com explains how the heat affects aviation.

The world has been hit by a series of heat waves the last few years. All "thanks" to climate change. These record high temperatures has resulted in a lot of grounded planes. But why is that?

There are two major reasons why airplanes can't fly in extreme heat. One; there's a risk that the engine will catch on fire. Two; when the air gets hot it expands and becomes less dense. When this happens the aircraft can't generate enough lift, as the wings require a certain amount of density to do so.

Larger aircrafts like the Boeing 747 and Airbus A380 can operate at temperatures around 126°F (52°C), but smaller ones like the 737 and the A320 start having troubles already at 118°F (47,5°C).

How do airplanes fly? 

To understand how the heat can ground a plane, you first need to understand how airplanes work.

To achieve "lift" airplanes need to be moving, which is where jet engines comes in. The engines' job is to move the airplane forward at a very high speed. When this happens, a moving current of air flows over the wings. The wings are designed to push the air downward to the ground, which results in an upward force known as lift (Newton's third law of motion: for every action, there is an equal and opposite reaction). In other words; wings generate lift by changing the direction of the current of air that occurs when the engines thrust the airplane forward. 

The lighter the air, the more difficult it is to achieve lift

So why is it more difficult to achieve lift during a heat wave? The answer is density (mass per unit volume). Air is a gas, which means that the molecules can both pack up and spread out - all depending on temperature. The molecules are constantly moving around, colliding into each other as well as into other things (read airplane wings). When the temperature increases the molecules start moving faster and the gas expands, resulting in less density. This means fewer air molecules colliding with the airplane wings during take off, making it considerably more difficult to achieve lift.

It is possible to compensate for lack of air density by for example increasing the speed, but for that you also need a longer runway - which is not always available. This is when airplanes are grounded because of heat.