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