"Air Conditioning System ?C General ?C Dealing with Design features. Air Conditioning Equipment - Commercial Passenger - Dealing with features. Applicable only to commercial passenger carrying aircraft. Desirable Design Features ?C General information for use of those concerned in meeting requirements contained herein. PURPOSE: ""ARP ?C This recommended practice is based on sound engineering principles and intended as guides for future standard engineering practices for aircraft industry."" This recommended practice is to be considered as being currently applicable and necessarily subject to revision from time to time@ due to rapid development of the aircraft industry. The following recommendations are based on practical engineering requirements for the design and testing of such types of heating and ventilating equipment as are now used on airplanes and for such as may be developed to meet the demand imposed in the field of service."