Vidual,
The helipad procedure has distinct advantages with respect to lateral visual cues. It is stated in AC 29-2C that two sides of the helipad should be in sight during the vertical ascent (however, it is only guidance material). It is noted that you quote a minimum ground level helipad size of 210 ft = 31 m; with lateral visual cues, that allows some leeway.
The surface of helidecks world-wide are generally built for a design D of 22m (the D of the S61). It was shown (in trials with the S61N in the early 90s) that with a deck of this size, visual reference is lost at about 20 ft. From that point pilots (inadvertently) start to drift backward to maintain visual reference. (Experienced offshore pilots almost always take their reference from the obstacles within the 150 degree sector at the side of the helicopter - this prevents a backward drift.)
In the referenced material OEI OGE is stated.
When the AW139 was certificated it was a helicopter with very good installed power. It could provide helideck Category A performance (meeting the 15 ft deck-edge clearance) within a TDP of 30 ft at maximum mass. In fact in most cases, there would be no drop down below the deck and min dip was well ahead of the rig. Weight growth has gradually eroded that power reserve. Because of this installed power, there was little (financial or operational) risk in an offshore trial leading to certification in Category A for this procedure. It would prove to be a very sound decision.
Even so, there would be occasions when the profile could not be flown (e.g. wind through the derick outside the cross-wind limits). As is stated in the Doc 10110 text:
Under these [ed. provided in the reference], and other, circumstances, the Commander might adjust the profiles to address a hazard more serious, or more likely, than that presented by an engine failure; regardless of these issues, the calculation of mass should still remain as defined in above.
The pilot would then have to revert to using it as PC2e - if within the operational approval.
As for the S92 nomenclature, I think this was originally the case but, for political/commercial reasons, it was changed. The reasons for not running an offshore flight testing regime and seeking approval were discussed above. The S76 approval flight trials took months and imposed a huge administrative/logistical/financial burden on the company - my guess is that Sikorsky, in concert with other manufacturers, took the view that a Category A helideck procedure would never be forced upon them. (The experience with the limited provision of S76 modification kits, that were required to apply the Category A procedure, probably showed that the uptake of the procedure was, in fact, limited in nature.)
Last edited by JimL; 5th June 2023 at 12:25.