Cats,
Thank you for coming back. I absolutely agree that not all airframe damage would have come from a reported incident. It was my bad for inferring that this would have been the case. But please allow me to outline a couple of points about how a military aircraft should have been bought and how it should have been maintained. (If you know these I apologise- I thought it might help those of a non-engineering background).
First, interchangeability. I'm not fully sighted on the details of how the Grob aircraft are built, but anyone buying a large fleet of gliders that are designed to easily come to bits on a regular basis (unlike normal military aircraft) should have made d**n sure that those bits could be swapped around, or replaced if required. In fact, I would have expected spare airframe parts to have been bought, with the requirement that these parts would have fitted any of the aircraft. Hand made or not.
Let's look at repairs, which are clearly of some interest. First, remember that we are talking military registered aircraft here. They have to comply with a series of key requirements to enter and stay in service, one of which is a comprehensive and accurate set of maintenance documents. One of those documents is the Topic 6, which is the repair manual.
A Topic 6 has to contain all the information needed to carry out repairs to the aircraft. It will contain standard approved repair schemes. (To pick up your point of a metal frame failing before the end of its life, that would normally have attracted a MF760 investigation, the end result of which could have included a new Topic 6 'standard repair scheme' to replace the frame).
It would also include a detailed map of the aircraft, telling maintainers what parts of the aircraft are 'primary', secondary', or 'tertiary' structure. These are usually colour coded. With this information, maintainers know what repairs they can apply to what areas of the aircraft. As I've previously posted, any such 'standard repair' would have normally been documented in a number of routine, well understood ways. Any external quality checks carried out by 22Gp, or the organisation that placed a support contract, would have checked routinely documentation of repairs.
if the damage found to an aircraft fell outside the information in the Topic 6, or fell into an area in which 'standard' repairs were prohibited, any Service unit would then raise a 'request categorisation' signal to the RAF's Repair and Salvage Unit (RSU). RSU would have inspected the aircraft, developed a repair (usually with DA support) and then applied the repair. RSU would have then made the relevant entries on the aircraft's documentation. There will be records of these routines.
What I'm trying (badly) to put over here is that on a Service aircraft repairs are easily and routinely managed and documented. And controlled. You simply don't go drilling holes in the structure, unless the Topic 6 says you can. You don't no 'non-standard' repairs - that's what RSU are for. The Topic 6 should also be maintained at a standard which allows maintainers to respond to emerging 'damage events'.
I said I wouldn't speculate any more, and I won't. All I will say is that not having a comprehensive and up to date Topic 6, or not funding MF760 investigations will, sooner or later, hazard the airworthiness of an aircraft fleet.
Best Regards as ever to those doing the repairs,
Engines