Airworthiness Directives and Service Bulletins
What are the differences between Airworthiness Directives and Service Bulletins?
ANSWER: Airworthiness Directives
(AD) are issued when the FAA finds that an unsafe condition exists in a product (aircraft, aircraft engine, propeller, or appliance.)
These AD's notify aircraft owners and operators of potential unsafe conditions and require special inspections, repairs, or alterations to correct the unsafe condition.Service Bulletins
(SB) are notices to aircraft operators from a manufacturer notifying them of a product improvement.
Alert service bulletins are issued by the manufacturer when a condition exists that the manufacturer feels is a safety related item as opposed to just a product improvement. These SB's usually result in the FAA issuing an AD. The AD will reference the alert service bulletin as a method of compliance with the airworthiness directive.
If a service bulletin is not an alert service bulletin or a bulletin referenced in an AD, it becomes optional and may or may not be incorporated by the operator.