There seems to be a trend in this thread to conclude that this accident was caused by dis-orientation. This may, after a full enquiry, be the case but there are still many unanswered questions.
The weather was fit for night shuttling with a useful 20+kts of wind to lean into. The crew had completed at least one night landing before the accident so were in the groove of night approaches. The crews at Blackpool regularly do several approaches each night so are well practised in low-level ops over the sea. The a/c was light with only 5 pax (10 can be carried) so performance wasn't an issue.
So what caused the experienced current co-pilot to roll away from the rig, accelerate and increase power, then increase the roll while pitching nose down then ask for assistance? This doesn't sound like classic disorientation, as he would have had the deck in site for most of the initial manoeuvre. Something else must have distracted the crew or caused the initial roll/pitchdown. Let us wait and see what the AIB final report says.
As a matter of accuracy for previous posts:-
Cyclic - the Dauphine has a go round button, which sets 75kts so long as the coupler is engaged - not likely during an approach.
Doublebogey - you are looking at this accident from, I believe, a Puma viewpoint. We spend most of our time with the height and heading hold engaged and it is unusual for us to do more that 20 night rig approaches a yr. A Blackpool Dauphin crew will do that in 2 days during the winter and go rounds are not unusual as during a shuttle it is not unrealistic to have to do at least one overshoot due to a deck crew not being ready. The transition from visual with a rig to the big black hole is an every night occurrence.
SteveMc - The Dauphin autopilot has 2 lanes one fed from the captain's and the other from the co-pilot's AI and compass. A discrepancy in info causes that channel to drop out with an A/P red alarm. The Trimble GPS ground speed function would be a hindrance in this sort of scenario as it is difficult to see and well away from the normal instrument scan.
Rotorspeed - yes the PNF has a responsibility to monitor the approach, call 55kts and acknowledge the commited (to land) call. This accident was not at the end of a rig radar approach so your comments about becoming visual do not apply
Let us wait for the full report before trying to come to a firm conclusion.
332M