Extreme heat grounds rescue helicopters. When is it too hot to fly?

As the temperature in California's Death Valley National Park skyrocketed to a nearly world record-breaking high, a group of motorcyclists traveling through the park found themselves in trouble.

But as the heat reached a record 128 degrees on Saturday, emergency medical helicopters were unable to respond to the scene because they can't safely fly in temperatures above 120 degrees, according to the National Park Service.

One of the riders died of heat exposure near Badwater Basin, and another had to be hospitalized in Las Vegas for severe heat illness. The other four were treated in the park and released.

Between 2007 and 2023, 76 people died from hyperthermia, or overheating, at one of the more than 400 sites managed by the National Parks Service, according to Backpacker Magazine. Research shows extreme heat fueled by climate change may only make these incidents more common in the future. The Earth has racked up more than 12 straight months of record heat, a bewildering climate change milestone.

Among global warming and extreme heat impacts, the grounding of flights, whether helicopter rescues or commercial aircraft, is another life-or-death consequence to be grappled with.

How high temperatures make it challenging to fly

Hot air is less dense than cold air, meaning there are fewer air molecules to generate lift according to David Ryan, an assistant professor of safety science at Embry-Riddle Aeronautical University's Prescott campus. Ryan said this means an airplane may need a longer runway and to pick up more speed to get off the ground.

"The hotter it is, the longer the takeoff length, and the heavier it is, the longer the takeoff length," he said.

Ryan said most modern airliners are tested to operate in temperatures above 120 degrees and in some cases up to 130 degrees. Most mainline Airbus and Boeing jets can take off safely up to about 122 degrees, and smaller regional jets often have a lower threshold for safe operations.

But Robert Thomas, an assistant professor in the aeronautical science department at Embry?Riddle’s Daytona Beach campus, noted there's no set temperature where it becomes too hot to fly because pilots must take into account a range of factors including temperature, elevation and winds to determine if an aircraft can perform adequately or not.

Thomas said "heavy duty" helicopters designed to do search and rescue missions or fight wildfires may be designed in a way that helps overcome performance issues brought on by high heat, for example being equipped with larger engines to help them carry extra weight.

"If you had a helicopter trying to rescue people, maybe you could get there, but...they might not have been able to actually take on extra passengers because the extra weight would have ruined their performance to get back," he said, adding that physical obstacles like mountains can make it even more challenging.

Thinner air also means fewer air molecules to mix with the aircraft's fuel, Thomas said. He said some airplanes also have turbine engines or turbocharges that artificially increase the density of the air.

"When it gets that hot, that helps, but it doesn't solve everything," Thomas said.

What happens when it's too hot for helicopters in Death Valley

When a visitor is experiencing a medical emergency while the temperature is over 120 degrees at Death Valley National Park, staff including EMTs will transport them via ambulance to an elevation of 3,000 feet, according to park spokesperson Nichole Andler. At that elevation, the temperature is typically 5 to 10 degrees cooler, and the visitor can be airlifted to a nearby hospital, she said.

If a visitor’s location is unknown, the California Highway Patrol or other local officials may use helicopters to conduct an aerial search in the park’s 3.4 million acres, though they may not be able to land or pick up any extra passengers.

The heat has always been a draw at Death Valley and the park has never closed due to high temperatures, Andler said. She said climate models predict that the region’s extreme weather will likely get more severe in the future and, like the Grand Canyon, the park will likely see an increase in heat-related illnesses as a result.

Increasing the temperature even by a few degrees will make it harder to get visitors in trouble out by helicopter, but Andler said staff have been working hard to educate visitors on how to prevent these emergencies in the first place.

“It's fun and it's exciting to be here when it is really hot. We know that that happens, and it is a very real scenario for visitors,” she said. “But we just want to remind everyone to make those good choices.”

Contributing: Natalie Neysa Alund and Zach Wichter, USA TODAY; Michael Salerno, The Arizona Republic

This article originally appeared on USA TODAY: How hot is too hot to fly? Why high temps sometimes ground flights