Action
Notice of proposed rulemaking (NPRM).
Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for CFM International, S.A. CFM56-5B series turbofan engines. That AD currently requires reviewing exhaust gas temperature (EGT) monitoring records to determine EGT margin deterioration, and for airplanes where both engines have greater than 80 [deg]centigrade (C) of EGT margin deterioration, borescope-inspecting the high-pressure compressor (HPC) of both engines. That AD also currently requires removing from service any engine that does not pass the borescope inspection and, if both engines pass, removing and replacing one of the engines with an engine that has 80 [deg]C or less of EGT margin deterioration. That AD also currently requires continuous monitoring of EGT margin deterioration on engines in service to prevent two engines on an airplane from having greater than 80 [deg]C of EGT margin deterioration. This proposed AD would require continuous monitoring of EGT margin deterioration, removing FADEC software version 5.B.Q and earlier versions from the engine as mandatory terminating action to the repetitive recalculating and EGT monitoring for certain engine models, and removing other certain engine models from service if the EGT margin deterioration is greater than 75 [deg]C. This proposed AD results from the need to reduce the affected engine models listed in AD 2009-01-01 from 25 to 19, the need to reduce the engine EGT margin deterioration removal threshold from greater than 80 [deg]C to greater than 75 [deg]C, the need to mandate a terminating action to the repetitive recalculating and EGT monitoring for certain engines, and the need to remove certain engines from service if the EGT margin deterioration is greater than 75 [deg]C. We are proposing this AD to prevent HPC stalls, which could prevent continued safe flight or landing.