Mandatory Service Bulletin MSB05-8B (camshaft gear) downgraded to non-mandatory. FAA will not issue AD. In April, my blog post “Continental’s War on Camshaft Gears” I wrote about Continental Motors’ issuance of Mandatory Service Bulletin MSB05-8B intended to compel owners of Continental 520- and 550-series engines (and a few IO-470s) to preemptively replace the older-style camshaft gears with a ...