ADs, SAIBs, and SBs
Airworthiness Directives (ADs), Special Airworthiness Information Bulletins, and Service Bulletins three ways in which information about aircraft safety is communicated to owners of aircraft. They are different things with different implications depending on which rules you are flying under. For general aviation aircraft that are flown under Part 91 of the FARs you must comply with ADs in order for your aircraft to be airworthy. i.e. if you haven’t complied with the AD (and that includes documentation) then in the eyes of the FAA and your insurance company your aircraft is not airworthy. For Part 91 operators, SAIBs and Service Bulletins are advisory—even though many SBs say in their text that they are mandatory.
It is a tremendous amount of work to read through all of the ADs that might be applicable to an aircraft to determine whether it applies to that specific aircraft. Several companies make software that IAs can use to simplify the process. (My IAs use Tdata.) The IA puts the serial number of the aircraft, engine, alternator, magnetos, oil cooler, etc. into the software and the software goes through the tedious process of determining which ADs apply to that particular aircraft. The owner or IA can then go through the logbooks and determine which ADs have been complies with. The software prints out a record of compliance that the IA signs and it is incorporated into the logbooks. This process is required at every annual inspection in order for the inspection to be signed off on.
Service Bulletins on the other hand are not issued by the FAA but instead are issued by the manufacturer of the part in question. It is up to the IA and the operator whether or not to comply with them. For example, SERVICE BULLETIN No. TP-14 Rev. 3 claims that replacement of Parker Hannifin vacuum pumps is mandatory. It is not. Only the FAA can mandate replacement of parts and then only by issuing an AD.
In between ADs and SBs are Special Airworthiness Information Bulletins (SAIB). “They are an information tool that alerts, educates, and makes recommendations to the aviation community. SAIBs contain non-regulatory information and guidance that does not meet the criteria for an Airworthiness Directive (AD).” As an owner/operator you should be aware of them and determine whether compliance is warranted. For example, SAIB: CE-14-23 was issued for Piper aircraft to alert A&Ps to a potential unsafe condition on inlet hoses. The inlet hoses for the carb look a lot like regular scat tubing that is used elsewhere in the engine. Unfortunately, scat tubing isn’t as rigid as inlet hose and it can collapse and cause the engine to quit from lack of air. Piper noticed that they hadn’t sold any inlet hoses in a long time and suspected that mechanics were using the wrong hose. My A&P checked, and sure enough I had the wrong hoses. Someone in the past, either through ignorance or cheapness, had replaced the $350 inlet hoses with $20 scat tubing.
Part 135 Charter Operations are usually required to comply with service bulletins as well as ADs—depending on how their certificate is written. Air Carriers and Freight operations have rules that I am not familiar with.