Under which conditions is compliance with an engine service bulletin mandatory?

Compliance with an engine service bulletin is mandatory when an airworthiness directive references it. Airworthiness directives (ADs) are legally enforceable regulations issued by the Federal Aviation Administration (FAA) or other regulatory bodies to correct unsafe conditions in aircraft, including engines. When an AD cites a service bulletin, it indicates that the information or actions in that bulletin are necessary to ensure the continued airworthiness and safety of the engine.

In essence, the referencing of a service bulletin in an AD elevates its importance, transforming it from a recommendation or advisory to a requirement that must be followed. This ensures that operators maintain compliance with safety regulations and uphold the safety standards expected in aviation operations.