- American Airlines policy says planes can reach 90 degrees before it's too hot to board passengers.
- Delta Air Lines, Southwest Airlines, and United Airlines do not set a maximum temperature limit for boarding.
Over the past few months, record-high temperatures have caused chaos on commercial airliners with people reportedly vomiting, passing out, and even being hospitalized due to extreme heat.
Sports producer and life coach Lauren Moses took to X (formerly Twitter) in July after sitting on a hot American Airlines aircraft for two hours in the Texas heat before eventually deplaning. She later told the Washington Post that the temperature outside was 99 degrees during the tarmac delay, and her plane had "minimal AC" during the ordeal.
According to an internal document reviewed by Politico, cabin temperatures on American can reach a sweltering 90 degrees Fahrenheit before the aircraft becomes too hot to board. This is more than JetBlue Airways' 85-degree limit — which recently changed from 80 degrees to cope with this summer's record-breaking heat wave and minimize delays.
American crewmembers are instructed to start cooling the plane once it hits 80 degrees, like closing window shades. And, the plane can still be boarded after it reaches 90 degrees in "extreme cases" but the "captain has the final authority," according to the internal document.
American did not immediately respond to Insider's request for comment.
While these carriers set a maximum cabin temperature limit for boarding, Delta Air Lines, Southwest Airlines, and United Airlines do not, the carriers told Politico.
In July, Delta came under fire for keeping passengers on a plane for more than three hours in Las Vegas where temperatures reached well above 100 degrees. The airline acknowledged the "uncomfortable temperatures inside the cabin" and the Department of Transportation — which regulates passenger comfort — is investigating the event.
Cooling an aircraft can be challenging because onboard air conditioning systems are not optimized for operations on the ground. During flight, aircraft cabins are cooled by mixing hot, pressurized "bleed air" from the engines with cold air from outside the plane — which can be down to -76 Fahrenheit at 37,000 feet, The Points Guy reported.
During a tarmac delay, however, this system does not work and airlines must rely on their engines for air conditioning, according to the Post.
The problem is that during lengthy delays, the engines burn more fuel, in turn adding costs. This prompts airlines to shut down the engines as a main cooling source and rely on their auxiliary power unit or other external equipment.
"We have several measures to keep our cabins comfortable on the ground and in the air, including pre-conditioning and using the APU connection for cooling prior to departure," United told Insider. "We also do some internal tracking to determine trends and adjust accordingly."
A Delta spokesperson told Insider that it uses air carts to pump air through the cabin and further aid cooling.
But these tactics are still sometimes not enough to counteract extreme outside temperatures. And the dozens of passengers onboard emitting body heat don't help.
"When you're on the ground and the doors are closed … you're basically the equivalent of the car sitting there in the parking lot with all the windows closed," Robert Thomas, an assistant professor of aeronautical science at Embry-Riddle Aeronautical University, told the Post. "You're kind of baking in the sun."
Currently, there are few laws to address hot planes. According to the DOT, airlines must provide "comfortable cabin temperatures" during tarmac delays, but does not define "comfortable."
However, the agency has held airlines accountable in the past. For example, in 2018, it issued a fine to Allegiant Air for its failure to regulate aircraft temperatures between 2016 and 2017.
"DOT takes seriously any reported incidents of extreme temperature conditions on passenger aircraft and will take action, consistent with its authorities, to ensure passengers are protected," agency spokesperson Ben Halle told Insider on Tuesday.
Airline unions are also taking action. In 2018, the Association of Flight Attendants-CWA petitioned the DOT to set hard guidelines that would tell airlines to keep their planes between 65 degrees and 75 degrees in flight or on the ground, with a strict maximum of 80 degrees.
"It's really absurd that we don't have these on the books already," Nelson said at the time. "These need to be standards just like any other safety regulation."