Apparatus for cooling electronic components in aircraft

A ram air cooling system for cooling electronic components in an aircraft provides automatic switching from a high ram air speed cooling mode (ACM) to a low ram air speed cooling mode (RAM). The cooling system receives variable speed ram air during the flight of the aircraft and includes an automatically controlled valve for either directing high speed ram air to a precooling means prior to cooling the electronic components or directing low speed ram air directly to the electronic components without precooling. The automatically controlled valve is controlled by programmable logic module means for comparing the cooling efficiency of the electronic components by precooled ram air with the cooling efficiency of the electronic components by the non-precooled ram air. The cooling efficiencies are calculated from temperature measurements of the ram air at several locations in the system of the invention. Preferably, the ram air cooling means is an air turbine which extracts energy from the ram air to drive a compressor that compresses and discharges heated air that exits from the housing for the electronic components after the ram air has performed its cooling function.