Statistics show that roughly 50% of all flight delays are attributed to control failures or malfunctions, while 30% involve bad weather. In certain regions, however, extreme heat can cause flight delays. Many people assume that planes can handle extreme heat. And while hot temperatures typically doesn’t cause any problems for most commercial planes, some planes are affected by it. So, how does extreme heat affect planes, and why can’t planes take off when it’s too hot outside?

Less Lift

Heat causes a myriad of effects for planes, one of which is reduced lift. Going back to the basics of physics 101, hot warm is less dense than cool air. When air warms, it expands, thereby reducing its density. For planes, this means their wings create less lift in extreme heat, forcing the jet engines to work harder while burning more fuel in the process. This Wired article explains how hot air affects planes’ lift. In extreme heat, the wings essentially collide with fewer particles of air — the air is less dense – so they are unable to produce strong lift.

Electronics Failure

There’s also a greater risk of electronic systems failure in extreme heat. All planes have a myriad of onboard electronics to control navigation, cabin climate, communications, landing gears and more. These electronics are pretty resilient and tested on a regular basis to prevent failure. When exposed to enough heat, though, they can fail or otherwise malfunction, creating a serious risk for the plane’s pilots, crew and passengers. As a result, some airlines will ground flights during extreme heat.

Ground Workers

A typical airport has dozens of ground workers outside the terminal. These workers are responsible for loading and unloading passengers’ luggage, directing incoming and outgoing planes on the runway, setting up steps for passengers and more. When it’s too hot outside, though, ground workers may experience heat-related illness. The Bureau of Labor Statistics (BLS) says that 37 workers died from heat-related illness in 2015. To protect ground workers from such injury, it’s not uncommon for airlines to ground flights due to extreme heat.

Will your flight be delayed due to extreme heat? Probably not. It typically takes extreme heat — in excess of 120 degrees Fahrenheit — to ground a commercial plane. And unless you’re flying in or out of an airport where temperatures are pushing this limit, it’s unlikely the airline will delay the flight. With that said, extreme heat is more likely to affect smaller planes as opposed to larger ones developed by Boeing and Airbus.