Airworthiness Directives; Boeing Model 757-200 Series Airplanes Equipped With Rolls Royce Model RB211-535E4/E4B Engines

This amendment revises an existing airworthiness directive (AD), applicable to certain Boeing Model 757-200 series airplanes, that currently requires a revision to the Airplane Flight Manual to ensure that the flightcrew activates the engine cowl thermal anti-ice (CTAI) system for both engines at the top of descent to avoid engine rundown (loss of engine power). This amendment clarifies the relationship between two existing AD's. The actions specified in this AD are intended to ensure that the flightcrew activates the engine cowl thermal anti-ice system for both engines prior to descent; activation of the engine CTAI system in the middle of descent could result in a compressor stall and subsequent engine rundown of multiple engines.