tucumseh:
The AAIB acted within their remit, but one can easily read between the lines and see they were acting in isolation,
“The ON/OFF switch was found at OFF, and an absence of substantial damage to the lift-toggle type switch, including its ramp mechanism, together with ground fire sooting patterns suggested that this had been the setting at impact. However, subsequent examination and memory read-out by Racal reportedly clearly showed that the unit had been operating until impact and it appeared that the switch position had in fact been altered by the effects of the crash”.
Seeing as the AAIB's very experienced inspector said that the RNS252 was switched off at impact and the BoI decided otherwise, the isolation of which you speak could not be made clearer. But then he was investigating an aircraft accident (within the AAIB remit) and it becomes ever more obvious that the BoI was not.