Design criteria utilized in the development of an air conditioning system for a 50–70 passenger jet aircraft for the short haul market are presented. Because the aircraft’s mission requires high speed over short stage lengths, special problems result. A short haul aircraft is described and related to the environmental system. Concepts for air conditioning that were considered as well as the one recommended are discussed. Final air conditioning design is reviewed relative to performance, operation, safety, reliability, and maintainability. The result is a package with larger than average cooling performance per passenger and design features not found in any other aircraft environmental system.