Perhaps, encompassing everybody's theory (and being slightly fanciful), the crew had just made the waypoint change when a spurious Eng Fail caption light came on, the crew then made a slight turn to the right to make landfall for an emergency landing and, due to the distraction, hit the Mull. I can't prove that to be correct (and actually doubt it to be correct), but there is no-one who can actually prove it wrong, based upon what little evidence is known. Absolutely no doubt whatsoever? I don't think so.
Or not much more fanciful:
At the waypoint change the handling pilot applied significant control inputs to turn left up the coast of the Mull causing the connections in the broom cupboard to fail(1) inducing sudden continued changes in fore and aft pitch(2)(3) causing DECU connectors to come partly loose generating multiple spurious warnings(4). The jolting and erroneous warnings overwhelmed the aircrew and uncontrolled the chinook flew on into the fog covered Mull.
Notes:
1. HoL Report Para 57: 57.
After the accident the investigators found that both inserts for the thrust balance spring attachment bracket had detached as well as most of the other inserts to both pallets. The AAIB stated, "as an insert could apparently pull out of the pallet without appreciable distress to the components necessarily resulting, the possibility that insert(s) had detached prior to the accident could not be dismissed" (para 7.4.2). In the Flight Control Summary the AAIB reiterated that "the possibility of control system jam could not be positively dismissed" and further stated that "little evidence was available to eliminate the possibility of pre-impact detachment of any of the pallet components" (para 7.4.9).
2. HoL Report Para 115:
115. Witness A also had personal experience of UFCMs in Chinook Mk 1s (QQ 792-6). In one case over a period of days an aircraft bounced vertically every time it was turned right.
3. HoL Report Para 111:
111. 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).
4. HoL Report Para 54:
54. The AAIB considered the engines and controls and because of the reported FADEC service difficulties investigated the DECUs in detail. DECU no. 2 remained partially functionable with deficiencies consistent with impact damage, and with no faults or exceedances traced in its memory of the last flight. DECU no. 1 had suffered gross fire damage with part of its casing melted away and severe damage to the interior components whereby its memories of exceedance and fault listing had been destroyed.
5. I have not seen the SuperTANs report, but nothing I have read shows that it recorded the attitude of ZD576.
Of course uncommanded pitch changes would mean that there was never any last minute flare.
Equally the lack of a chain of events of co-incident broom cupboard and DECU failures would explain the lack of any further accidents.
Like Brian, I cannot say that this scenario occurred, but to find the pilots guilty of gross negligence then to my mind you have to prove this scenario could not happen.
EG