In
an International Standard Atmosphere the temperature is +15ºC at sea level and
has a lapse rate of 1.98ºC per 1,000 up to 36,090 feet.
At FL330 (33,000 feet) the temperature
is
+15º - (33 x 1.98º)
= +15º - 65.34º
=
- 50.34ºC