What is the difference between a Service Bulletin and an Airworthiness Directive in ground operations?

• A. Service Bulletins are mandatory regulatory requirements; Airworthiness Directives are manufacturer recommendations.
• B. Service Bulletins are manufacturer recommendations; Airworthiness Directives are mandatory regulatory requirements.
• C. Both are optional guidance with no regulatory impact.
• D. Service Bulletins apply to flight operations only; Airworthiness Directives apply to ground operations only.

Answer: (B)

The main distinction is regulatory authority and enforceability. Airworthiness Directives are mandatory rules issued by the aviation authority to address a safety problem and must be complied with to keep the aircraft legally airworthy. Service Bulletins are issued by the manufacturer as recommendations for maintenance actions or design changes; they’re guidance to operators, not enforceable on their own. An SB becomes mandatory only if the aviation authority adopts it into an AD or otherwise requires it through regulation. So, SBs translate as manufacturer guidance, while ADs are binding regulatory requirements.