Having a letter on file on the subject is pretty haunting to the authority, because if there ever is an accident that could be traced back to them not taking action, they are culpable (or at least a good lawyer could make a case for that).
That is exactly what I did in order to get the FAA’s attention. In my second letter I told them that I was absolving myself of any responsibility* and passing the problem on to them. I also told them that if an accident occurred and it was traced to the problems outlined in my letter I would offer my services to the legal teams taking the company and the FAA/DGCA into court. Based on this perceived threat they went to the manufacturer of the system and as a result the VP and the program manager were fired. The design however was not modified so the problem still exists and the FAA now has two letters on file.
On a more recent note I obtained an AD on the same aircraft and it dealt with an inspection and possible changes of some of the parts based on that inspection. The whole procedure was ass backwards and was in total conflict with how the system was originally designed. I contacted the FAA and the Canadian MOT and both told me that the FAA version was translated from the French and the Canadians copied the FAA’s version. I told them of the possible error and the Canadians contacted the DGCA, as did I. I never got a reply from any of them and there is a possibility that the FAAs version has exacerbated the original problem that I told the FAA about several years prior to that time.
*In a tort case the trial lawyers can reach downward into the design and production staff in order to assess blame.
