Following up on last week, Ask the Pilot weighs in on exactly why the heat in Phoenix is grounding airplanes:
Extreme heat affects planes in a few different ways. First, there are aerodynamic repercussions. Hotter air is less dense than cooler air, so a wing produces less lift. This is compounded by reduced engine output. Jet engines don’t like low-density air either, and don’t perform as well in hot weather. Together, this means higher takeoff and landing speeds — which, in turn, increases the amount of required runway. Rates of climb are also impeded. Performance parameters require that a plane be able to climb away safely following an engine failure, and this might not be possible. Engines also are subject to internal temperature limits — exhaust gas temps, etc. — beyond which operation isn’t permitted. When it’s really hot outside these limits are easier to exceed.
Then you’ve got the simpler, more tangible effects: overheating electronics, increased brake temperatures, cabin cooling issues, and so on. Airplanes have a lot of internal machinery, and much of it runs hot to begin with. Throw in triple-digit temperatures, and things begin to break down. And let’s not forget the effects on ground support equipment and, of course, the people working outside.
It's currently a balmy 39°C in Phoenix. That's almost tolerable, with enough air conditioning.