Would Affect All 520- And 550-Series Engines Over the weekend, Continental Motors issued Mandatory Service Bulletin MSB05-8B affecting all 520- and 550-series engines (plus a few IO-470s). Normally, Part 91 operators are not required to comply with manufacturer’s service bulletins. However, when Continental issues a Mandatory Service Bulletin, it means that they have asked the FAA to issue an Airworthiness Directive (AD) to make compliance compulsory. That’s the case with MSB05-8B.
Source: aero newsExtremely Costly AD May Be In The Works For Continental Engines