Perhaps I can help a little to clarify matters here.
Whenever any maintenance was carried out on RN aircraft, the supervisor for that work was required to ensure that the person carrying it out had the required qualifications, training and publications available to do the job. Units and departments also took care to ensure that any work on a safety critical item was carried out by an experienced tradesman. One of the basic requirements of any tradesman, as well as supervisors, was to understand the way in which the system they were working worked. If required to dismantle and reassemble a drogue shackle, they would have been required to understand that shackle's function, how it operated, and the key checks to be carried out after reassembly. These 'competences' were checked on a regular basis for all ratings, using a rolling 'performance check' system that was mandated on all FAA squadrons and departments. In essence, the RN pursued a 'competency based' system backed up by active local quality assurance.
Due to their particularly hazardous nature, any work on ejection seats was specifically authorised to a few personnel who had also done a special 'seat safety course'. If at all possible, work on ejection seats at first line was avoided by returning the seat to the bay and replacing it with a serviced item. One of the main reasons the RN did this was because we knew that, having dispensed with a specialist Weapons trade, the 'Weapons Electrical' ratings we had were less experienced than their forbears. hence the special precautions that were taken. Now contrast that approach with what the SI established happened on the RAFAT, where inexperienced tradesmen, with no authorised training, worked in pairs on the aircraft, supervising each others' work, using handy pre-printed forms.
Sorry if I'm repeating myself. We can all go on as much as we like about how many threads should have been showing, what sort of nut was used, and what APs were being used, and who issued what warnings. The core issues with this tragic accident are (in my view) staring us in the face.
An RTI that wasn't actually required to make the seat safe was issued by the engineering authority, possibly at the behest of the operating authority - and apparently nobody involved in the process kept a single record of how that happened.
A safety critical system was being taken apart every 50 hours. By itself, that should have raised massive warning flags. However, once again, no records seeem to exist on how that risk was supposed to be managed.
The RAF failed utterly to ensure that the people carrying out this safety critical task had the experience, training or supervision required to make it safe.
The poor s*d who actually overtightened the shackle on that day had, by the time he did it, been comprehensively failed by a number of people. Not by the system - by people not doing the jobs they were given to do.
The solution to this sort of problem is not, repeat not, more regulations and more instructions. It's this - do what we're already supposed to be doing.
Best Regards as ever to all those who are doing the work for real at the coal face today,
Engines