Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 757-200 series airplanes modified by supplemental type certificate (STC) SA1727GL. This proposal would require deactivation of the air-to-ground telephone system approved by that STC. This action is necessary to prevent the inability of the flight crew to remove power from the telephone system when necessary. Inability to remove power from the telephone system during a non-normal or emergency situation could result in inability to control smoke or fumes in the airplane flight deck or cabin. This action is intended to address the identified unsafe condition.