American Airlines has canceled 38 flights in and out of Phoenix on Tuesday afternoon because of extreme heat.
The cancellations are for operations by smaller regional jets that have lower maximum operating temperatures than full-size airliners. Those jets can't operate when it's 118 degrees or above.
American warned passengers over the weekend that it may have to ground flights during a heat wave that could send the temperature soaring to near 120 degrees. Spokesman Ross Feinstein says the late afternoons are the peak affected times.
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The airline is letting Phoenix passengers flying during the peak heat Monday through Wednesday to change flights without a fee. The forecast calls for a high of 119 Tuesday.
Extreme heat creates changes in the air density that make it harder for airplanes to take off. Airlines respond by imposing weight restrictions, such as carrying less cargo and fuel. But in some cases, they will ground flights during the peak heat.