This SAE Aerospace Information Report (AIR) covers, and is restricted to, the behavior of air under conditions of critical and subcritical flow at temperatures less than 500 degrees F.

This AIR is intended to provide basic information and theoretical background on proper types of test equipment and calculation procedures for use in measuring air in critical and subcritical flow conditions, as are usually encountered in jet engine starting applications and to provide guidance in the construction of test apparatus. Additionally, a method for simplifying the calculations performed by technicians is presented.