jp,
Your words:
fugitive technical fault which seized the aircraft systems for about 20 seconds between waypoint change and impact, but them which vanished three secondes before impact leaving no post-impact evidence
John Blakeley's words in 2003:
Although the Board found that most of the attachment brackets were detached from the control pallets they decided that detachment was likely to have occurred during the post-impact break up of the aircraft. Thus the Board considered any pre-impact control malfunction as "highly unlikely". This is a remarkably "brave" conclusion given that they had clear evidence of a fault that was still the subject of a serious defect signal investigation at the time of the accident. The Board is understood to have based their decision on the AAIB investigation, but Mr Cable's evidence to the House of Lords certainly does not support such a positive conclusion. This was summarised as follows:
He (Mr Cable) further explained that the detachment of the pallet inserts and the components carried by them could possibly cause a restriction or jam. "It would be very difficult - impossible - to dismiss the possibility that there had been a restriction and evidence had not been found" (Q 196). This explanation is readily understandable given the crowded equipment in the broom cupboard. A balance spring is some 6 inches long by 1½ inches in diameter and its mounting bracket about 1½ inches long.
The evidence of the RAF Odiham Unit Test Pilot, Sqn Ldr Burke, to the House of Lords is also relevant in this area. This was summarised as follows:
In relation to possible jams Squadron Leader Burke explained that, due to the complexity of the Chinook control system, a jam caused by a loose article such as the balance spring in the broom cupboard in one of the three axes, pitch, yaw or roll, could lead to quite random results in all three axes sometimes and certainly in two of them. He had personal experience while lifting off from the ground of a jam in one axis affecting the other two (Q 935). He also referred to the problems of DASH runaways in Chinooks of both marks causing temporary loss of control of aircraft (Q 929).
(My bold).
In your need to be simple, I suspect that you have conveniently forgotten this.