Exgrunt
I had not appreciated that the GPS unit was a separate box from the Supertans. Was it ever examined to see what, if any, internal data it held separate from that fed into the Supertans memory?
You have identified a strange weakness in the investigation (or perhaps not so strange, given the political imperative).
The AAIB report makes no mention whatsoever of the GPS. (Remember that the RTS informed aircrew that GPS Initial Operating Capability had not yet been declared by the US DoD, and warned them that the “Error” message was “meaningless”).
In discussing the RNS252 SuperTANS, the AAIB said this;
“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”.
Thereafter, the AAIB simply refers the reader to the Racal report, as if it is comprehensive, factual, valid and verified - when they obviously doubt all of this.
Now, any reasonable reader would twitch violently at the above paragraph. Nobody would dispute the AAIB has vast experience in such matters and the author (Mr Cable) makes it quite clear he thinks the switch was OFF at impact; and his scepticism about the Racal conclusion is clear. He must have examined hundreds, if not thousands, of such fire damaged switches in his career, and could be relied upon to come to the correct conclusion. Clearly, there was a conflict to be resolved. Equally clearly, the MoD party line was that Racal’s report took precedence.
One obvious question is not asked. Does setting the switch to OFF actually power down the unit completely, or does it “simply” remove indications but continue to calculate away in the background? This standby mode is a common concept. Could it indicate an attempt at resetting? If so, it could mean the crew switched off the RNS252 – we already know they were told not to rely on it and did not trust it. We also know that they had only just returned to flying a Mk2, and the respective Releases to Service did not complement each other. That is, the meaningless “Error” warning was not in the Mk1 RTS. From a Human factors viewpoint, they'd be thinking "Both aircraft have the same kit, which version do I believe?".
The worst part is this. Based on the Racal report into the remnants of the RNS252, the MoD concluded, ludicrously, that this meant the entire Nav System was both accurate and serviceable. There is no mention of other sub-systems being tested; except the Rad Alt Tx/Rx which, as we know, was found to be both faulty and defective. (And due to the paucity of testing info and equipment, vital power interrupt tests were not possible). Nor is there any mention of the quite important fact that many systems were not cleared for use in the first place. For example, the AAIB report simply says the VOR/ILS was “ON”, but no-one has ever addressed the fact it was not cleared for use. Why were these anomalies never challenged or investigated by the BoI? Answer - Because CA and ACAS, and their subordinates, simply could not afford to allow any investigation to go there, revealing the fabrication that was the Release to Service. But now it HAS been revealed.
My conclusion is that the technical investigations were limited and disjointed - something John Blakeley has said for years. The AAIB acted within their remit, but one can easily read between the lines and see they were acting in isolation, without vital information. For example, they made no mention of the classified equipment that was on board, which a BoI witness declined to give details of and was omitted from the RTS; yet it could be vital in an EMI sense. On RNS252, Racal were allowed to dream up an unvalidated and unverified method of extracting and analysing data from the RNS252: to be fair to them though, they said nothing outrageous, merely claiming that their simple calculator/indicator worked. It was MoD who made the false claims. The Reviewing Officers? They, of course, determined immediately that the aircraft was both serviceable and airworthy; when manifestly it was neither.