The summer travel season got a rocky start in late June when thunderstorms, coupled with airport staff shortages across the U.S., caused as many as 7,700 flight delays and 2,200 cancellations in a single day.
But a lightning strike isn’t the most likely way travel plans get snarled. Passengers are learning the hard way this summer that high temperatures can be as disruptive to on-time departures as visibly inclement weather.
This week extreme heat has rippled across much of the U.S. and Europe. Cities experiencing record-breaking temperatures have included Miami; Tampa; Portland; San Antonio; and New Orleans. In Phoenix, July 12 marked the area’s 12th consecutive day of temperatures reaching over 110 degrees. The heat wave is said to have affected a quarter of the American population.
Federal Aviation Administration data show that for many airports summer weather is responsible for far more delays that winter weather — partially because it takes a less extreme weather event to send operations into a tailspin. Chicago O’Hare, for instance, had almost twice as many weather delays from June to August 2022 as it did from January to March 2023. At New York’s LaGuardia, there were 35 percent more weather delays in summer 2022 than the following winter.
Additional data from aviation analytics firm FlightAware shows that from January to March 2023 there were 402,881 flight delays in the U.S. — representing 19.6 percent of all scheduled departures — whereas in the summer months of June to August 2022, there were 544,462 delays, or 23.3 percent of the country’s flights.
Winter storms can cause more widespread havoc, however. Of a dozen events that caused mass disruptions to U.S. flights in the last 12 or so years, 8 stemmed from winter storms; only 3 related to hurricanes. (The 12th was COVID-19.) Heat waves may not result in large-scale breakdowns in service but are instead a constantly humming engine of daily disruption in which season-long impacts can add up.
“When temperatures exceed 39 degrees centigrade (102 Fahrenheit), it becomes really problematic for airlines,” said Bijan Vasigh, economics and finance professor at Embry-Riddle Aeronautical University in Daytona Beach, Fla.
Heat thins the air, which reduces the lift that helps planes take off. The hotter the temperature, the more power is required to get airborne.
“The hotter and more humid the surrounding air is, the more aircraft engine and airfoil performance degrade,” echoes Kathleen Bangs, a former commercial pilot who’s now a spokesperson for FlightAware. “Aircraft get their best performance during cool or cold temperatures as the density of the air increases.”
In hot weather, pilots may decide to delay flights or reduce the weight aboard the aircraft by dumping excess fuel, bumping bags or even taking off some passengers; ultimately, in a game of wait-and-see, they can run into such issues as running out of fuel or exceeding time limits on staff shifts. For passengers, that can mean flight disruptions, route changes or delayed luggage.
The logic around where heat can ground flights is counterintuitive and doesn’t always correlate to where temperatures are hottest. See snowy Denver: The Mile High City has more delays in summer than winter, when comparing only those disruptions that are attributed specifically to weather.
“Elevation also has an effect,” Bangs explains. “Taking off at higher-altitude airports during extreme heat can have (additional) limitations on weight.”
