AD FAA-2014-0521

We are adopting a new airworthiness directive (AD) for all CFM International S.A. (CFM) CFM56-7B series turbofan engines. This AD was prompted by a dual engine thrust instability event that resulted in the overspeed and in-flight shutdown (IFSD) of one engine. This AD requires modification of the engine by removing full authority digital engine control (FADEC) software, version 7.B.V4 or earlier, installed in the electronic engine controls (EECs) on CFM56-7B engines. We are issuing this AD to prevent a thrust instability event, which could lead to overspeed and IFSD of one or more engines, loss of thrust control, damage to the engine, and damage to the airplane.