A good example of how a mechanical failure leads to a manufacturer’s Service Bulletin (SB) being issued:
Accident: NTSB Accident Brief of Accident
Which leads to…
Service Bulletin: Robinson R44 Service Bulletin SB-86 – Rotor RPM Sender Magnets
Side note – good job on the safe landing!
Service Bulletin’s are not mandatory* – that would be a FAA Airworthiness Directive, which often evolve from SBs.
* See Mike’s comment below