1023 -1013 =
10hPa x 30 = 300ft. Altitude in ISA conditions = 25,300ft.
FL250 ISA = +15ºC – (2º x 25)
= -35ºC
OAT = -50ºC
Dev. =
-15ºC
Difference
between true altitude and pressure altitude is calculated as:
4ft per1,000ft
per ºC ISA deviation = 4 x 25.3 x 15 = 1,518ft
True altitude
= 25,300 – 1,518 = 23,782. Or use
CRP5