With respect to this thread and the subject in hand, you should all be aware that the views expressed here are being read and noted. As far as 26500lbs' post is concerned, and specifically HF (not just in the North Sea but from the Cougar 851 report and the accident in the Far East - i.e. other offshore provinces), there is a culture issue. it would appear that we have an insidious problem that has been allowed to develop because it was not recognised that the introduction of automation would also necessitate a change in our operating procedures and CRM (culture). This is extremely well illustrated by the subject of this thread - the L2 accident at Sumburgh.
We pick up the accident as soon as the choice was made to fly the LOC/DME; this NPA does not have a step-down profile and is therefore a good candidate for a stabilised approach (not CDFA because there was no procedure and the helicopter was not equipped for it). With a stabilised approach even if it was elected to fly in 3 axis mode either the V/S or the A/S mode could have been engaged with the other set as a monitored parameter (i.e. a constant).
To make this a 'monitored-stabilised' approach the PF would have had to decide, from the information provided in the ROD panel, the V/S and the A/S. If this had been done, both pilots would have been oriented to the key constants, and any adjustment that had to be made would have been with respect to the gradient provided by the check heights at the DME check points and applied to the non-coupled constant. The PM would have been completely oriented to the key parameters to monitor and the bounds of the trajectory within which the approach should be conducted. Any departure from the bounds, so established, would have required a challenge from the PM and an adequate response from the PF.
However, if you carefully consider the AAIB report you will see that this was far from a stabilised approach because to fix the V/S (couple) you also have to establish and maintain a reference A/S. This cannot be done on a decelerative approach!
The PF opted for a three axis approach with the V/S coupled but, in the brief, indicated that there would be a reduction of speed to 80kts. Coupling the V/S and flying a stable approach can only be achieved by having a constant A/S; if a decelerative approach is chosen then the required V/S to achieve the notional trajectory will also be a variable.
The effect of this can be seen on the descent below the notional glide when the A/S was reduced (with the V/S coupled).
My point is that in order for the PM to function as a key member of the crew in the monitoring role, he/she must know the boundaries of normality; in the accident, those boundaries were not known because the trajectory was not fixed. In consequence, the PM could not report on a diversion from the V/S or the A/S (and in fact also did not report on the check heights at the DME points - clearly there were too many variables).
It is not known whether the CHC SOPs specify the required regime for a NPA however,an approach flown in accordance with an SOP should indicate the mode of flight, the key constants and the variables. If any of the non-coupled constants tend to the limit, the PM can make the appropriate calls and the PF the necessary response, or, failing that, the PM can take the appropriate action. Without a deterministic approach (SOPs) the crew cannot act as a team - with the inevitable results that we have seen.
Not operating in this manner indicates that we have not yet embraced the cultural changes, associated with automation, that are required in training, operating, and crew resource management. These changes are a necessity that were identified in fixed-wing when similar incidents/accidents occurred at the time of the introduction of the glass cockpit.
Mars