Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Allison Engine Company 250-B and 250-C series turboshaft engines. This proposal would require replacing existing beryllium copper main fuel control (MFC) bellows assemblies with Inconel 718 stainless steel welded MFC bellows assemblies. This proposal is prompted by reports of leaking MFC bellows assemblies resulting in an uncommanded minimum fuel flow condition, loss of engine fuel flow control and subsequent forced landing. The actions specified by the proposed AD are intended to prevent MFC bellows assembly leakage, which can result in an uncommanded minimum fuel flow condition and subsequent loss of engine fuel flow control.