These specifications are written to cover the subject of exhaust hot air type heaters under three classifications, namely. A EXHAUST HOT AIR TYPE HEATERS - GENERAL - Dealing with features applicable to all makes and users. B EXHAUST HOT AIR TYPE HEATERS - MILITARY AND COMMERCIAL -Covering features applicable to military and commercial aircraft. C DESIRABLE DESIGN FEATURES - General information for use of those concerned with meeting requirements contained herein.