aviation_

I have the same experience. I'm an American expat so sometimes people will explicitly call out celsius for my benefit or as a joke, but yeah, nobody ever says celsius when they talk about the temperature here.

"What's the temperature?"

"It's gonna be 21."

"Got it, thanks."

That's how it usually goes.

I don't live in the UK but nearby in Europe. I know a handful of Brits but have never heard them express temperatures in Fahrenheit (and they know I'm American, so if they switched I always figured it would be for my benefit). Is that really true about the hot weather thing?

Just this past week for example, my colleagues were complaining about the 33 degree heat wave, were excited for the weather to drop back down to the 20s on Friday, and were complaining about the random 31 degree heat wave coming on Saturday.

US Aviation in the sense of the "aero" part of aerospace is still very much US Customary Units. I don't have enough experience with the "space" part of aerospace to comment on that. We still use pounds of thrust, slug and pound masses, psi for pressures and so on for things related to turbines and engines and so on. Strangely, we use kelvins instead of Rankines but that's the only exception I can think of.

Edit: Note that this isn't to say that aerospace engineers prefer the US units or that we don't know how to use the metric system or anything, it's just how it is. In this particular field, it's just the accepted standard.