Types of control: This recommended practice covers automatic cabin temperature control systems of the following types for pressurized and unpressurized cabins: Type I ?C Proportioning. Type II ?C on-off@ or Cycling. Type III ?C Floating@ including modifications thereof. PURPOSE ARP-This identification is used for design and dimension standard or performance specifications based on sound engineering and intended as guides for further standard engineering practices for the 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.