(Newser) – The heat wave in the Southwest has made it too hot for some planes to fly out of Phoenix. With temperatures expected to hit a near-record 120 degrees Tuesday, American Airlines has had to cancel more than 50 regional flights on Bombardier CRJ aircraft, which have a maximum operating temperature of 118 degrees, reports the Arizona Republic. "Hot air is less dense" than cold air, which makes it harder for planes to get off the ground, explains author and airline pilot Patrick Smith, per Business Insider. "This affects the output of the engines as well as aerodynamic capabilities, increasing the required runway distance and reducing climb performance."

American Airlines says 45 flights out of Phoenix Tuesday have been canceled. Another seven flights between Phoenix and Tucson were canceled Monday, 12 News reports. Larger Airbus and Boeing jets have maximum operating temperatures of 126 or 127 degrees, and so won't be affected unless temperatures in Phoenix go off the charts, the airline says. On Monday, the city recorded a temperature of 118 degrees, tying the record for the day set last year, the Washington Post reports. The all-time Phoenix record of 122 degrees was set on June 22, 1990, when the extreme heat caused many aircraft to be grounded. (Read more Phoenix stories.)

