"I just want to know why a good system was changed."
In my view the old system was “good” , i.e better than the present-day, for two reasons:
Firstly, because there was no corrosive Compensation Culture and its associated lust for vindictive penalties against any individual or any organisation which could possibly have influenced the accident. When you see the sums paid out by MoD for relatively trivial incidents these days, it makes you wonder how there is any money left for actual defence.
Secondly, and most importantly, deaths in service in peacetime training were generally accepted as the norm and would barely make the headlines – a natural consequence of operating high-performance military hardware in Cold War training scenarios. The Wittering village churchyard contains the graves of at least 10 Harrier pilots whom I knew personally. Other Wittering pilots’ graves are located elsewhere.
As another example, 1BR Corps in Germany normally expected at least half a dozen fatalities (and scores of serious injuries) per major summer exercise. Compare that attitude with the hysterical breast-beating that goes on nowadays with the loss of any service person in an accident.
I’m not saying that attitude was good or bad – it’s just a fact.
I accept that the old BoI system was vulnerable to pressure from very senior officers hoping to avoid blame. As to how often that occurred, then I am not so sure. In my experience of old-style BoIs, they came up with the right answers more often than not. We changed procedures/equipment where possible and got on with the job.
In the old system, to avoid pressure of rank on the President, as soon as it was suspected that a relatively senior officer (Wing Commander or Group Captain) was likely to be blamed, then the authorities sent in a new President who outranked the suspected officer.
All of this was done relatively quickly, the Post-Accident 48 hour signal giving a best guess into what had happened (without prejudice to the eventual findings), thus forestalling immediate repeats of the same accident. Nowadays this does not seem to happen. There is an information blackout and aircrews are left waiting for months before there is a hint of what actually happened and who was to blame. Rumour takes over, with predictable effects on morale.