Summary
We propose to adopt a new airworthiness directive (AD) for all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. This proposed AD was prompted by a determination that a repetitive test is needed to inspect the components on airplanes equipped with a certain air distribution system configuration. This proposed AD would require doing repetitive testing for correct operation of the equipment cooling system and low pressure environmental control system, and corrective actions if necessary. We are proposing this AD to detect and correct latent failures of the equipment cooling system and low pressure environmental control system, which could result in smoke in the flight deck and possible loss of aircraft control.