Outside temperature in the cruise

[Mungo Man]

Another question from a new FO! I was in the cruise the other day and noticed the static air temperature was minus 70 degrees celcius! Never heard of it being that cold in the cruise before. No doubt someone has exerienced colder conditions though - so lets hear about it!

[Intruder]

-74 is the coldest I've seen.

[Mungo Man]

That's cold Intruder! What type were you in? We had to decend into warmer climes becuase the Embraer was outside its envelope. Are other aircraft limited by minimum temperatures for cruise?

[Intruder]

747 on a northern Canada route.

We're mainly limited by fuel temp, but there is an absolute OAT limitation as well. The Operating Envelope chart sez -54 at FL200, decreasing linearly to -81 at 390 and above. I'm surprised to see an UPPER temp limit of -40 at FL430 and above, as well...