http://www.digitaljournal.com/life/travel/extreme-heat-grounds-nearly-50-regional-flights-out-of-phoenix/article/495564

Near 120 degree temperatures ground some flights in Arizona

Posted Jun 20, 2017 by Karen Graham
Quite a number of regional flights out of Phoenix on Tuesday were grounded, as extreme heat, which is expected to last into the weekend, kept some planes on the runway.
Bombardier CRJ American Eagle
Bombardier CRJ American Eagle
Bombardier
According to a statement from American Airlines, the company's American Eagle regional flights use the Bombardier CRJ aircraft, which has a maximum operating temperature of 118 degrees Fahrenheit. Tuesday's temperature is expected to near 120 degrees.
“Our smaller regional operations — those that use our CRJ aircraft types — will be most affected by the heat,” the airline’s communication specialist Kent Powell told CNN. “We really aren’t expecting any change to the operation with our mainline aircraft.”
There is a plausible explanation for the cancellations. Hot air is less dense than cold air. This makes it harder for planes to get off the ground, forcing pilots to use more thrust and often requiring a longer runway. The CRJ is a smaller plane used for regional flights and its engines have a limit of about 117 degrees.
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Larger planes have higher maximum operating temperatures, such as those planes operated by Boeing, 126 degrees, and Airbus, 127 degrees. But American Airlines says its customers can rebook flights or request a full refund by contacting reservations at 1-800-433-7300.
This is not the first time that heat has caused a disruption in air travel in Phoenix. Back in 1990, the temperature got up to 122 degrees in Phoenix. Planes were grounded because the temperatures listed in flight manuals didn't go high enough, and pilots didn't have instructions on what settings to use.
But times have changed, along with temperature extremes. Higher temperatures have led to aircraft engines being manufactured with higher temperature tolerances. As it is now, 45 flights have been grounded today and the rest of the week is still up in the air, so to speak.