Hot weather proves a problem for pilots

Much of Arizona rarely sees a cloud, and it usually offers great weather for flying. Phoenix is one of the top four US locations for number of flying days per year. But last week more than 50 flights were cancelled, not because the weather was bad but because it was too hot.

Hot air is less dense that cold. The wings of an aircraft generate lift by effectively pushing down on the air, and less dense air provides less lift. An aircraft needs a certain amount of lift to take off and gain altitude. The hotter the weather, the less dense the air and the less lift the wings produce.

As the heatwave affecting the south-western US took hold, temperatures in Phoenix rose to a scorching 48C, making it too hot for some aircraft to fly – or at least that was how media reported it.

This may be slightly misleading. The cancelled flights were on Bombardier CRJ regional jets, small short-haul airliners. It was not that the Bombardiers could not physically get off the ground in the heat, but that they lack safety certification to fly in temperatures above 48C. Airbus and Boeing airliners do not necessarily produce more lift, but they have been certified for 52C or more, and so were not affected.

Testing aircraft in extreme conditions is expensive, and Bombardier probably assumed that such temperatures would be too rare to affect operations. A few more heatwaves may make high-temperature certification more of a priority.