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True Altitude - ATPL Navigation

  • flying
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flying created the topic: True Altitude - ATPL Navigation

What formula do I work out to find true altitude? Appreciate your feedback on this.
Ben
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  • Stuart Tait
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Stuart Tait replied the topic: True Altitude - ATPL Navigation

Relationship of true and calibrated (indicated) altitude:

TA= CA + (CA-FE)*(ISADEV)/(273+OAT)

where

TA= True Altitude above sea-level

FE= Field Elevation of station providing the altimeter setting CA= Calibrated altitude= Altitude indicated by altimeter when set to the altimeter setting, corrected for calibration error.

ISADEV= Average deviation from standard temperature from standard in the air column between the station and the aircraft (in C).

OAT= Outside air temperature (at altitude)

Substituting:

FL170 represents a pressure altitude of 17,000 ft
We know that the OAT is -10°C
Indicated altitude is 17,500 ft

ISADEV = (stdISAtemp - (PA * (lapserate)) - differentialfmstdtemp )

TA = 17500 + (17500-0) * (15-17500/1000(2)-(-10)) / (273 - (-10))

TA = 17500 + 17500 * +10 / 283

TA = 17500 + 665.39

TA = 18165
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