US Airways had to cancel 18 flights at the weekend because of the heatwave which has hit the American West.
Spokesman Todd Lehmacher told CNN that planes are certified for take-off at up to 118 degrees, but the temperature crept up to 119 degrees in Phoenix on Saturday.
The National Weather Service issued an excessive heat warning for large parts of California, Nevada and Arizona, and a heat advisory for other parts of Nevada.
An entire crew of nineteen firefighters died in the town of Yarnell, about 80 miles north-west of Phoenix, after the hot temperatures and wind led to a fire raging out of control.
The fire, which was started by a lightning strike, destroyed half of the 500 homes in the small town.
Many of the excessive heat warnings continue until Wednesday when temperatures are to drop a couple of degrees.
Meteorologists said the intense heatwave was caused by a high pressure system hanging over the western United States.
"I’m not worried as much about the people who have lived here a while," said Sgt. Troy Stirling, police spokesman in the Lake Havasu, Arizona, near the California state line.
"It’s more the tourists coming into the area, even from Southern California, who aren’t used to this kind of heat."
