These recommendations are written to cover the general requirements of helicopter air conditioning and are subdivided as follows: Air Conditioning System: Dealing with the general design aspects. Air Conditioning Equipment: Design requirements for satisfactory system function and performance. Desirable Design Features: General information for use of those concerned in meeting requirements contained herein. Winterization and Pre-heating. PURPOSE: The purpose of this recommended practice is to provide the aircraft industry with a standard to which helicopter air conditioning systems may be designed for civil aircraft. The detailed recommendations are based on practical engineering requirements for the design@ installation@ and operation of heating and ventilating equipment used on helicopters.