ATPL Q's using Temps at flight levels
Hope someone can help here:
Having trouble with questions asking for Temperatures at flight levels, usually using Local Speed of Sound and often asking to add ISA + and -.
e.g 1
"Given the following, calculate TAS in ISA conditions.
Mach 0.83, Temp at FL300 -39°C"
I used LSS=38.94 x √Temp (kelvin), but didn't get the answer of 489kts
e.g 2
"Given the following, calculate the corresponding flight level in ISA.
Mach 0.767, TAS 477 kts"
So the answer is FL167, but how???
Is there a formula to work out temperature at altitude, like what is the temperature at FL33 in ISA conditions?
If any one smarter than me can help out I'd be very thankful.
Cheers!