New York (CNN) — Passengers may not expect a hot, sunny summer day to be the reason their flight gets delayed or even cancelled. But heat waves can be hazardous for flying.
High temperatures affect aircraft performance, resulting in travel delays, weight restrictions, fuel stops and, in some cases, even cancellations.
“A hot summer day can impact the operation just like snow or ice,” according to Embry‑Riddle Aeronautical University professor Cary Grant, who spent decades flying as a pilot with United Airlines.
The reasoning comes down to the science of aerodynamics.
Airplanes rely on denser air to help the engine and wings generate lift for takeoff.
High temperatures cause air molecules to spread farther apart, making the air less dense or thinner. When the temperatures get very hot, takeoff becomes substantially more challenging.
“The engines require air to go through the engine and propel it back out. If there’s less air coming in the front, there’s less air going out the back,” Grant said. “The wings require air to go over the wings. If there’s less air going over the wings, it creates less lift.”
While the physics can be dense, it comes down to two options for airlines to ensure a safe departure: Either they need to use a longer runway to gain more speed, or they must reduce the weight of the aircraft.
But some airports do not have the space or budget to extend their runways, leaving airlines with the only other feasible solution to lighten the aircraft’s load.
“In some cases, airlines can reduce aircraft weight to safely take off by offloading cargo or passengers. They also could reduce the amount of fuel loaded to accommodate all passengers, in which case they may have to add a fuel stop to reach their intended destination,” the Federal Aviation Administration said in a statement to CNN.
But sometimes the heat is too severe to fly at all.
“While reducing weight can be an option, temperatures sometimes exceed the maximum temperatures the plane was subjected to during testing. When that happens, there is no data in the operations manual that would allow the plane to be flown,” the FAA said.
Not only can extreme heat affect aircraft performance, but it can also have effects on crew members and passengers.
“When we think about heat it affects the engines, it affects the airplane, but it also affects the people,” Grant said. “If you think about how well you perform when you’re hot, your performance goes down.”
Airport ground crews in hot climates can be exposed to oppressive heat, and airlines must protect their health.
“We also have a robust heat management plan in place for our employees to ensure they have adequate hydration and places to cool down,” Southwest Airlines said in a statement to CNN.
Inside the cabin, the airlines want to make it comfortable for their customers.
“That’s why flight attendants sometimes ask passengers to close their window shades as the plane pulls to the gate to help keep the interior as cool as possible,” Southwest added.
July was the hottest month on record for the contiguous US going back to 1895, according to National Oceanic and Atmospheric Administration.
Last month, American Airlines was forced to remove 32 passengers from a flight out of Las Vegas during an extreme heat wave, according to CNN affiliate KVVU.
“It’s either 32 people decide to alter their plans or all of us are going to alter our plans, because the plane literally cannot take off,” passenger Jared Guynes said he was told.
The problems caused by hot weather are becoming more common. In recent years, heat waves are increasingly hotter and more frequent, according to the Environmental Protection Agency.
And that means passengers are frequently left with little choice but to be prepared for delays and cancellations in hot weather.
“I would say never be alarmed by it because the airline’s always looking out for safety. That’s their No. 1 priority,” Grant said. “But my best recommendation for everybody is to be flexible and look at it as an advantage to get something from the airline that you’re paying for.”
The-CNN-Wire
™ & © 2026 Cable News Network, Inc., a Warner Bros. Discovery Company. All rights reserved.