The Federal Aviation Administration issued a Special Airworthiness Information Bulletin (SAIB) on May 2 in which it reiterated issues with Lycoming cylinders shipped between September 1, 2013, and April 30, 2015, but the agency has declined to issue an Airworthiness Directive to enforce replacement of these cylinders. The suspect cylinders were the subject of a Mandatory Service Bulletin (MSB) in October 2018.
This is a companion discussion topic for the original entry at https://www.avweb.com/ownership/faa-special-bulletin-stops-short-of-ad-on-lycoming-cylinders