On the hottest days, thinner air can make it harder for aircraft to get off the ground safely. Airlines may have to lighten the load by removing passengers or cargo, or carrying less fuel. But even less extreme heat can create similar challenges at airports with higher elevations or shorter runways. With heat waves searing parts of the United States and Europe this summer, Las Vegas illustrated how extreme heat can interfere with air travel. In July 2018, some airlines bumped passengers at Denver International Airport to later flights as temperatures reached 98 F (37 C), KDVR-TV in Denver reported.