Field results demonstrate reliability gains through improved cooling

The principle that improved cooling enhances the reliability of electronic equipment has long been accepted. Recently, questions have been raised concerning improved cooling and the expected magnitude of reliability gains. A recently completed analyses of operational results, comparing avionic reliability achieved on F-15 aircraft under significantly different cooling conditions, shows cooling-related reliability gains that exceeded predictions. The study was conducted by MDA F-15 engineering personnel under a contract awarded by the Air Force (WR-ALC/LFEFF). F-15E aircraft are equipped with an ECS package that produces 40°F inlet temperatures for forced air cooled equipment. Heat loads and flow rates are such that average equipment exhaust temperatures are 115°F. The corresponding temperatures created by the ECS package in the F-15C/D aircraft are 85°F and 124°F, respectively, resulting in mean equipment temperatures that are 27°F higher than experienced on the F-15E aircraft. Seventeen forced air cooled electronic Line Removable Units (LRUs), common to both the F-15E and F-15C/D aircraft were selected for a performance comparison. Reliability performance was measured using Mean Time Between Maintenance-Type 1 (MTBM-1) in Flight Hours, as reported by Air force field data systems. The data from several bases cover a one year period. The F-15E equipment, which benefits from improved cooling, showed an aggregate MTBM-1 that was forty four percent (44%) better than that achieved by the F-15C/D equipment. These measured results, attributable to better cooling, met or exceeded predicted improvements in reliability