Summary
We propose to adopt a new airworthiness directive (AD) for all CFM International (CFM) S.A. CFM56-7B series turbofan engines. This proposed AD was prompted by a dual engine thrust instability event that resulted in the overspeed and in-flight shutdown (IFSD) of one engine. This proposed AD would require modification of the engine by removing full authority digital engine control (FADEC) software, version 7BV4 or earlier, installed in the electronic engine controls (EECs) on CFM56-7B engines. We are proposing 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.