Overview
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. |