Why This Week Could Be Hell For Air Travelers

It’s sure getting hot out there. The Northeast and Midwest is in a heat wave, with sky-high temperatures and humidity all week, according to the National Weather Service, which warned that the looming heat dome “could see temperatures topping the century mark.”

That’s going to make for an unpleasant flying experience for many air travelers, for several reasons. First, extremely high temperatures can force airlines to reduce the weight being carried on planes, which in turn can cause flight delays and passengers getting bumped.

By 1 p.m. Eastern time on Monday, more than 2,500 flights within the U.S. were delayed—a huge jump up from the roughly 1,400 delays reported at 10 a.m., according to FlightAware, a free app that provides real-time, historical, and predictive flight tracking data. Expect the number of delayed flights to climb throughout the day, perhaps topping last Friday’s tally of over 8,300 delayed flights.

“Hot temperatures reduce air density, and that means that the airplanes can produce less power or thrust,” explains Dr. Bob Thomas, assistant professor of aeronautical science at Embry-Riddle Aeronautical University in Daytona Beach, Florida. “When it’s hot like that and you’re creating less thrust, you essentially have to lower the weight of the airplane to be able to use the available runway and also to meet the climb restrictions that are set out by the FAA.”

But Dr. Thomas says there isn’t a magic temperature that universally triggers the decision to reduce the number of passengers from a flight. “It’s literally an airport by airport thing, and even a runway by runway thing, because different airports and different runway lengths are all different. In the mountain regions, they’re at a higher elevation, which makes it even worse,” he says, adding that it can get so hot in an area like Phoenix that airlines have no choice but to cancel flights. “Essentially, the runways become too short.”

According to tarmac rules put in place by the Department of Transportation (DOT), airlines are required to let passengers off the plane after three hours for domestic flights and four hours for international flights. But extremely hot days can mean that passengers sit in sweltering cabins for hours when the plane is stuck on the tarmac, either waiting to takeoff or after landing.

The worst-case scenarios make headlines. Last July, a United Airlines flight was delayed on the tarmac at Newark airport for seven hours, trapping passengers without food, water or air conditioning, according to local news reports. The same month, a Delta flight was held on the tarmac in Las Vegas for four hours on a day when temperatures peaked at 111 degrees, reportedly with no air conditioning. The heat inside the aircraft was so intense that multiple passengers reportedly vomited and passed out, and two people ended up at the hospital, Reuters reported.

Essentially, an aircraft’s cooling system only works when it’s in the air. When the airplane is flying at 35,000 feet and taking sub-zero temperature air in, the cabin crew can set the in-cabin temperature to whatever they like.

“The air conditioners on airplanes work differently than you’d expect,” Dr. Thomas says. “Typically, you have an air conditioner and a big hose that will pump cool air into the airplane while you’re at the gate. So once you detach from that, and you’re sitting on the ground with no air flowing through the airplane, essentially there’s no way to cool the air down before it gets put into the cabin.”

Tips for Summer Flying

A weather issue in one region can become a national air travel problem because of how airlines reuse planes and crews for multiple trips during the day, creating a domino effect. A late-morning flight delay in Boston, for example, can prevent a plane from getting to Dallas for an early-afternoon departure, which can in turn bump back the same plane’s late-afternoon flight out of Chicago.

The simplest way for travelers to reduce the risk of a flight disruption is by booking an early flight, when temperatures are cooler. “Especially down in the Southeast or anywhere in the South where there are afternoon thunderstorms every day, it’s always smarter to take the very first flight in the morning,” Dr. Thomas says. “You avoid the risk of thunderstorms delaying and changing routes and that kind of stuff.”

FlightAware can tell you if your plane is on schedule or give you an early heads-up that a problem may be brewing. Enter your flight information, and then click the “Where is my plane now?” link just under the flight number. If your plane is behind schedule, you can take action accordingly. FlightAware also lets you sign up for alerts to be sent via email or text if there are changes associated with your flight. You can search by flight number or city pairing.