JFZ90
You clearly missed this summary in the Sunday Times article. It wasnt just a problem before the crash that got sorted. Newspaper articles on complicated subjects like this are always far shorter than they ought to be
Documents seen by The Sunday Times show that the aircraft was brought into service despite evidence that key connectors could loosen in flight, putting control of the engines at risk.
The papers show that the problem was still in existence after the crash and that aircrew were subsequently warned to check during the flight that the connectors had not loosened.
Here on pprune of course I have space to give more detail of the documents:
The quote in the original November 1993 priority signal coinciding with the Mk2's introduction into service and instigating the SI states:
A case has occurred where a DECU connector worked loose in flight. The connector loosened sufficiently enough to affect the functioning of the FADEC system.
Then in August 1994, two months after the Mull crash, an SI is issued which carries the identical wording. Two months later, there is an authorisation for aircrew to check that the connectors have not begun to disconnect in flight.
I was told on Friday by the MoD that if FADEC failed the system simply reverted to a manual system and could be flown as per the Mk1. Lord Phillip also said as much, presumably having been told the same as me.
Lord Phillip said in his report:
If the system failed it was designed to default to the reversionary mode and a predetermined setting and the pilot would revert to manual engine trim.
I have now received documentation showing that this is not the case.
Reversionary Control Mode. Failures (hard faults) during reversionary control system operation are indicated by failure of the FADEC system to respond to ENG RPM TRIM (collective grip) control. Once failed, the reversionary system faults to fixed fuel flow. The reversionary system faults to fixed fuel flow. The reversionary control system fixed fuel setting does not allow for any proportional control using the ECL. The ECL only allows the engine to be set from a fixed fuel setting to an engine off setting. Changes in power settings on the effected engine are not compensated for directly by the FADEC system and may allow engine overspeeding up to the overspeed limiter control set speed. It is advisable to minimize power changes during this condition. In addition, the effected engine should be shutdown prior to descending for landing.
Primary and Reversionary Mode. If the primary control system fails and the reversionary system has already failed, the FADEC reverts to a fixed fuel flow setting. Changes in engine power settings will not be controllable on the effected engine. The engine should be secured prior to descending for landing.
More than that. The article says the existence of the SI had been noted in an appendix to the BoI but its contents not revealed. I now know that while it certainly should have been noted, it was not. In fact the appendix to the BoI report stated unequivocally:
Serial Nos and classes of relevant modifications embodied and of SIs and STIs complied with; NONE
So they knew of the existence of the problem when the Mk2 was introduced in November 1993 and issued an SI in a priority signal. They then formalised the SI in August 1994 two months after the crash. Then two months later in October 1994 authorised aircrew to check during flight that the connector had not begun to disconnect. But the BoI was not made aware of this SI. Then Wratten and Day blame the pilots. Did they not know the SI existed? Then Lord Phillip appears to have been misled into believing that FADEC failure would simply result in reversion to manual operation.
I think most people would find this all a bit suspicious.