This doument contains information on cooling of modern airborne electionics,cmpasizing the use of a heat surface which separates coolant and compoent.It supplements the information contained in AIR 64 for the draw through method and in AIR 728 for high mach number aircraft. Report contents includ basic methods,characterstics of coolants,application inside and outside of the "black box"use of thermostatic controls to improve reltability and system design.charactersics of typical cooling components are treated sufficiently to permit selection and to estimate size and weigh.