Summary
We propose to adopt a new airworthiness directive (AD) for certain model 767-200, -300, and -300F series airplanes. This proposed AD would require doing certain wiring changes, installing a new relay and necessary wiring in the cabin air conditioning and temperature control system (CACTCS), and performing an operational test of the cooling pack fire suppression system. This AD results from reports of loss of avionics cooling due to an unserviceable relay installed on a panel as part of the CACTCS. We are proposing this AD to prevent loss of electrical equipment bay cooling and the overheating of flight deck instruments, which would result in the eventual loss of primary flight displays, an unusually high pilot workload, and depressurization of the cabin.