American Airlines was forced to cancel more than 40 flights out of Phoenix’s Sky Harbor Airport and delay seven others yesterday, after local temperatures exceeded the 118°F/47.8°C operating limit of the Bombardier CRJ regional jet.
“The issue,” the Washington Post explains, is that “air is less dense when it is hot, which can affect a plane’s ability to get off the ground. That’s why manufactures place maximum operating temperatures on their aircraft.”
Which meant that “extreme heat, which is forecast to impact Phoenix June 19-21, may affect your upcoming travel plans,” AA cautioned in a message to customers. “If you are scheduled to arrive and/or depart Phoenix during this time period, we recommend you change to an earlier or later flight, or connect via a different city, in order to avoid any disruption.”
In a more detailed explanation of the physics behind the problem, Wired notes that larger planes from Airbus and Boeing can handle temperatures up to 126°F/52.2°C, before running into the same constraint that grounded the Bombardiers in Phoenix.