Hot temperatures in Denver require Alaska Airlines to refuel in Spokane
Alaska Airlines flight 432 from Denver International Airport to Anchorage International Airport was forced to make a refueling stop in Spokane on Monday due to takeoff restrictions in Denver. This is the result of Denver’s high elevation and warm summer temperatures.
Because warm air is less dense than cold air, hot temperatures can lower the air density significantly. This does not pose a problem at most major airports around the world. Airports like Seattle-Tacoma, Los Angeles, Dallas-Fort Worth, JFK, and Toronto all sit under 1,000 feet (300 meters) elevation. By contrast, Denver sits at 5,434 feet (1,656 meters).
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Approximate flight path for the AS432 route with a refueling stop in Spokane. (Ingalls Weather)
Hot days can lead to the “density altitude” at Denver rising closer to 8,000 feet (2,440 meters) meaning the departing aircraft has to take off as if it were at that altitude instead of the airport’s actual altitude. The lower air density impacts aircraft in two ways: less lift is generated by the wings and the jet engines produce less thrust.
The result is that a plane needs to go faster to take off but has less engine power to get there. Denver International Airport was built to handle this to an extent, but on hot summer days you can only do so much. The runway at Denver is the longest among public use airports in North America at 16,000 feet (4.9 km). Compare to 11,901 feet (3.6 km) at SeaTac.
Weight restrictions aren’t new in Denver. The old Stapleton Airport frequently had this problem with its longest runway at 12,000 feet (3.7 km). The runway length at Denver’s new airport was a factor in it being built so far from the city center.
Restrictions hit a significant number of aircraft types around 95ºF (35ºC). An analysis of weather data from 2015 to 2025 shows an average of 22 days at or above 95ºF each summer. Denver averages two days each summer at or above 100ºF (38ºC), though 2021, 2022, and 2024 all had five to six.
Airlines respond to these conditions by reducing aircraft weight. Cargo and checked bags often get trimmed first but sometimes passengers may be rebooked on another flight. Another option is to reduce the fuel the plane holds at takeoff with a refueling stop at a lower elevation airport, which is what Alaska Airlines did Monday with AS432.
AirportElevation (ft)Elevation (m)La Paz, Bolivia13,3254,062Quito, Ecuador7,8742,400Mexico City, Mexico7,3162,230Jackson Hole, Wyoming6,4511,966Denver, Colorado5,4341,656Albuquerque, New Mexico5,3551,632Nairobi, Kenya5,3301,624Reno-Tahoe, Nevada4,4001,341Tehran, Iran3,3051,007
Denver is the largest airport in the United States that has to account for this but it isn’t the only one. Other notable high-altitude airports that get hot in the summer include Albuquerque, Reno-Tahoe, and Jackson Hole. Globally we can add La Paz/El Alto, Bolivia, Mexico City, Mexico, and Quito, Ecuador.
Air density can be a problem for departing aircraft at low elevation airports when temperatures are extremely high. Phoenix-Sky Harbor International Airport and Harry Reid International Airport in Las Vegas are the most prominent examples of this in the United States.
In 2023, airlines asked passengers to deplane voluntarily in Las Vegas when temperatures hit 116ºF (47ºC). One carrier moved a flight to Beijing to depart at 01:00 during the overnight hours specifically to dodge the heat during another Las Vegas heat event. LaGuardia in New York and Reagan serving Washington, D.C. can occasionally have this problem due to their shorter runways.
The Tri-Cities Airport in Pasco, Washington, is less exposed to air density problems. Temperatures rarely exceed 110ºF (43ºC) in the Columbia Basin and the airport serves regional flights that are served by lighter aircraft taking trips that require less fuel. High heat problems are a bigger issue for large widebody jets, though American Eagle did have to cancel 40 regional flights out of Phoenix in 2017 because temperatures exceeded the operating range of the aircraft they had scheduled to serve those routes.
The featured image is an Alaska Airlines Boeing 737, the same type of aircraft that was used on the DEN-ANC route Monday, landing at San Francisco International Airport. (Bill Abbott)
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