STFs etc
Because the regulations governing STFs are so vague and ambiguous, some of this is opinion.
When regs covering whole aircraft are vague (e.g. Def Stan 05-123, 00-970) I always found it wise to consult those applicable to Avionic equipment, because they are the best available. Despite being scrapped two years ago, without replacement, any sensible project manager still has his personal copy to hand. The solution to almost every airworthiness related problem aired on this forum is contained in that one Def Stan. (But D/Stan can no longer provide you with a complete copy, and haven’t been able to since 1993).
These state that the equipment equivalent, a Trials Installation, can be (a) Temporary or (b) Retainable.
As the regs are so vague and, as stated by Engines, STFs are a peculiarly RAF device, the question posed here often arose. The answers were equally vague but official MoD airworthiness training says an STF can be Retained and used operationally, subject to a Certificate of Design and inclusion in the Safety Case. Then, and only then, the RTSA may issue a Service Deviation. The point here is that the CAR/MAR was not amended, due to time constraints – clearly implying operational imperative was a factor. This was meant to catch up in due course. The SD would dictate how long the STF was valid for. At this point the system failed as there was seldom follow-up action.
This process has changed now, but the principles remain valid; however legacy aircraft will take some time to conform.
Having said all that, there is a contradictory regulation (as ever!) which says one cannot infer such a thing, there must be a positive statement. My personal view is that the retention of STFs for operational use is fine, but subject to basic rules (above) being implemented. The reason why the system became abused was simple – AMSO slashed funding to implement the regs in 1991, and then issued orders that they were NOT to be implemented. No Configuration Control or maintained drawings. Hence, progressively invalid Safety Cases and RTSs. This wasn’t incompetence on the part of project staff, EAs or RTSAs. It was a deliberate supplier-led policy. The basic rules were not implemented, leading to a situation whereby numerous STFs (and SRIMs, NSMs etc) were either “safe but didn’t work” or “worked but were unsafe”. In particular, systems integration disciplines and interoperability were routinely ignored, so that a STF that was “safe and worked” could subsequently be rendered unsafe by another STF. And, of course, the Safety Case was not maintained at the In Use Build Standard.
This is where detailed specialist knowledge of Modification procedures comes in (and airworthiness in general). When AMSO ruled in 1991 that he didn’t need such expertise, the inevitable happened. It didn’t happen overnight of course, but it was progressive throughout the 90s and got to the stage it was impossible to resurrect. However, the effect was predictable and predicted, but senior staffs chose to ignore it.
This is where I wholeheartedly agree with Tourist. The result, a complete dumbing down, has eroded flexibility and hamstrung front line. But everyone must understand this hamstringing is not as a result of Haddon-Cave. That report merely brought well established facts to the attention of those in power who HAD to do something. But I believe the MAA reaction to be driven by the fact there remains so little expertise in MoD to plan resurrection. Lack of expertise breeds inflexibility.
It is easy (and reasonable) for Haddon-Cave to say “implement the regs”. Fifteen years ago I’d have given us a chance. Eleven years ago (11th January 2000) DPA’s Deputy Chief Executive (DCE – 3 Star) was given an internal report in response to the Public Accounts Committee’s report “Modifying Defence Equipment”. He took no action. Demonstrably, had he taken even the simplest action and reiterated mandatory regulations should be implemented, subsequent accidents would have been avoided. I don’t know why he took no action (he didn’t reply to the report) but, to be fair, his immediate boss (CDP) had the previous year upheld rulings that airworthiness regs were NOT to be implemented; echoing AMSO and AML rulings from the early 90s. Management sets the tone.