Radio Rack Cooling in Present Commercial Aircraft

Limited heat dissipation from the necessarily compact electronic equipment installations of airline aircraft has been a problem to commercial air carriers for many years. To deal with this problem, United Air Lines, in August, 1955, began equipping fleet aircraft with a forced air electronic equipment cooling system, with the following objectives: 1) improvement of electronic equipment reliability, 2) reduction of crew discomfort caused by electronic-equipment generated heat in the flight deck area, and 3) evacuation of any smoke from the flight deck area which might arise from electronic equipment failure. Observation of electronic equipment maintenance records during the subsequent transition period from convection to forced air equipment cooling shows characteristic failure rate trends which indicate the dependence of equipment reliability on operating temperature. These patterns occur independently in fleet records for the Convair 340, and DC-6 and DC-6B fleets, in time phase with the progress of conversion to forced air cooling in the fleet. These records, in conjunction with other comparative testing of forced cooled and convective cooled equipment installations indicate that forced air cooling provides an effective answer to airline equipment heat problems.