Service Bulletin (SB)

A Service Bulletin is issued by the manufacturer to recommend an inspection, modification or improvement. Unlike an Airworthiness Directive, a Service Bulletin is usually advisory rather than mandatory — though regulators sometimes make one mandatory by issuing an AD that references it. Its completion status affects an aircraft's condition and value.

Why it matters: service bulletins are the manufacturer's channel for recommending improvements, inspections or modifications. Unlike airworthiness directives they are generally not mandatory for private operators, but they represent the manufacturer's current view of the fleet's needs — and regulators sometimes convert important ones into ADs later.

Compliance status with significant bulletins is therefore both a condition signal and a value signal: an aircraft whose owner incorporated the important SBs was maintained proactively, and it is already compliant if a bulletin later becomes mandatory. Buyers comparing candidates should ask for the SB status list, not just the AD list.