AD FAA-2015-0681

We are adopting a new airworthiness directive (AD) for all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. This 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 AD requires doing repetitive testing for correct operation of the equipment cooling system and low pressure environmental control system, and corrective actions if necessary. This AD also requires, for certain airplanes, installing new relays and doing wiring changes to the environmental control system. We are issuing this AD to detect and correct latent failures of the equipment cooling system and low pressure environmental control system, which, in combination with a cargo fire event, could result in smoke in the flight deck and/or main cabin, and possible loss of aircraft control.