Summer is well and truly setting in. For some, it means lying out in the sun and enjoying the outdoors but in Arizona, it means staying inside as much as possible.

The heat in the south-westerly desert state has reached such a point that planes are now being grounded. American Airlines said that 43 flights scheduled to leave from Phoenix's Sky Harbour Airport were cancelled on Tuesday (20 June) as the heat outside was higher than the plane's maximum operating temperature.

The affected planes were Bombardier CRJ regional aircraft, the airline said, which have maximum operating temperature of 118F (48C). In Phoenix, the high for Tuesday was 120F (49C).

American Airlines said that only the Bombardier CRJ flights were affected as their Airbus and Boeing aircraft have maximum operating temperatures of 127F and 126F respectively.

The heat also meant seven regional flights were delayed.

The specifications for maximum temperature are set by the aircraft manufacturers, the airline said, and the elevation of the airport is also taken into account.

In an email to customers, the airline said that the extreme heat on Monday, Tuesday and Wednesday may affect flights and recommended that customers check the status of flights, notably those during the hottest part of the day - from 3pm to 6pm local time - before leaving for the airport.

Customers affected by Tuesday cancellations can request a refund from the company.

American Airlines added that the National Weather Service forcast for Wednesday (21 June) put the highest temperature below the CRJ's maximum operating temperature. "At this time, we do not anticipate any further disruption to flights on Wednesday, but we will reevaluate tomorrow morning in case the forecast is adjusted," the airline said.