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Hofmeister
21st Mar 2006, 20:44
Having done a Google search and studied the ICAO tables, I was wondering whether any PPruner knows a good rule of thumb for calculating altimeter error in extremely cold temperatures. Thanks in advance.

bookworm
22nd Mar 2006, 07:15
Having done a Google search and studied the ICAO tables, I was wondering whether any PPruner knows a good rule of thumb for calculating altimeter error in extremely cold temperatures. Thanks in advance.

0.35% per degree C difference. e.g. 1000 ft above datum, ISA - 20 degC, altimeter overreads by 7% or 70 ft.

Empty Cruise
22nd Mar 2006, 09:19
Or +4% for each 10 deg. C below ISA :ok:

karimi
22nd Mar 2006, 09:23
Delta Alt true = Delta Alt ind +/- (4 x ( T - T std) x Delta Alt ind) / 1000

Delta Alt is the air layer from wich you have to correct the temperature
( ie if the aircraft is at 2000 ft sea level but at 1000ft over the ground, you wil have to correct 1000ft)

+ if temp over std
- if temp below std

Ex: Aircraft 2000ft above the groun on std - 25 ( indicated temp at 2000ft= -14 deg cel) => true alt = 2000 - (4 x 25 x 2000) / 1000 = 1800 ft