The extreme heat forecast for Phoenix on Tuesday has caused the cancellation of 20 American Airlines flights out of Sky Harbor International Airport.

According to a statement from American Airlines, the American Eagle regional flights use the Bombardier CRJ aircraft, which has a maximum operating temperature of 118 degrees. Tuesday’s forecast for Phoenix included a high of 120 degrees, and the flights that are affected were to take off between 3 and 6 p.m. MT.

Customers affected were told to contact American Airlines for rebooking options or to request a refund.