In the West Coast, the scorching heat is breaking records, causing massive power outages and prompting flight cancelations. American Airlines canceled around 50 flights in and out of Phoenix (PHX) last week due to skyrocketing temperatures in Arizona.

The airline issued cancelations for smaller regional jets with a lower maximum operating temperature than the full-sized aircraft from manufacturers like Boeing and Airbus. The smaller regional planes can’t operate in 118-degree weather.

“Our smaller regional operations — those that use our CRJ aircraft types — will be most affected by the heat,” said Kent Powell, communications specialist, American Airlines. “We really aren’t expecting any change to the operation with our mainline aircraft.”

To give passengers a heads up about cancelations, the carrier announced the airline would have to ground flights during a heat wave where temperatures could reach near 120 degrees. To help accommodate passengers impacted by cancelations, American Airlines waived change fees in Phoenix.

The extreme temperature changes in the density of the air make it hard for planes to take off. While airlines limit the weight inside the aircraft to ensure successful departures, canceling flights is the only option when a heat wave reaches over 118 degrees.

While flight cancelations due to extreme heat are rare, they may become more common. According to a study by the University of Hawai’i, cancelations due to heat waves may become more popular as 50 percent of the world’s population will experience a month of deadly heat waves every year by 2100.

Last week, excessive heat warnings were issued for inland California, southern Nevada and parts of southwest Arizona, with more than 29 million California residents under a heat warning or advisory.