International Standard Atmosphere (ISA)


The International Civil Aviation Organization (ICAO) established the International Standard Atmosphere (ISA) as a way of creating an international standard for reference and performance computations. Because the standard atmosphere is a derived set of conditions that rarely exist in reality, pilots need to understand how deviations from ISA affect instrument indications and aircraft performance.

The ISA consists of the following:

Condition Value
Pressure (Sea Level) 29.92" Hg.
Temperature (Sea Level) 15° C
Lapse Rate 2°C per 1,000 ft.


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