How does a Service Bulletin (SB) differ from an Airworthiness Directive (AD)?

How does a Service Bulletin (SB) differ from an Airworthiness Directive (AD)?

• A. SBs are mandatory and legally enforceable; ADs are manufacturer recommendations
• B. SBs are manufacturer recommendations; ADs are mandatory and legally enforceable
• C. Both SBs and ADs are voluntary guidelines
• D. SBs are legal requirements; ADs are advisory

Answer: (B)

The key idea is who issues the action and whether it must be followed. A Service Bulletin comes from the aircraft or parts manufacturer and shows recommended inspections, modifications, or repairs to improve safety or reliability. It’s advisory, not legally required by aviation regulations, unless a regulatory directive later makes it mandatory. An Airworthiness Directive comes from the aviation authority and is a regulatory requirement. When an AD is issued, operators must comply within the specified timeframe to keep the aircraft airworthy; failing to comply can have legal consequences and can affect flight status. So the best match is that Service Bulletins are manufacturer recommendations, while Airworthiness Directives are mandatory and legally enforceable. It’s also common for an AD to reference or require actions that a manufacturer suggested in an SB, but an SB alone does not become mandatory.

The key idea is who issues the action and whether it must be followed. A Service Bulletin comes from the aircraft or parts manufacturer and shows recommended inspections, modifications, or repairs to improve safety or reliability. It’s advisory, not legally required by aviation regulations, unless a regulatory directive later makes it mandatory.

An Airworthiness Directive comes from the aviation authority and is a regulatory requirement. When an AD is issued, operators must comply within the specified timeframe to keep the aircraft airworthy; failing to comply can have legal consequences and can affect flight status.

So the best match is that Service Bulletins are manufacturer recommendations, while Airworthiness Directives are mandatory and legally enforceable. It’s also common for an AD to reference or require actions that a manufacturer suggested in an SB, but an SB alone does not become mandatory.