Thanks dangermouse.
After some reflection and having considered what you have said about the use of groundspeed (GS) as a reference for the (low speed regime of) Category A procedures, I am persuaded that you are right.
Because the AW189 MFD is extremely busy, conspicuity of the ‘digital GS’ display below the ASI strip might be an issue – particularly if it is flown single pilot. The integrity of the DGPS signal also has to be assured as has its accuracy (this will have a knock on effect on the MMEL limitations of the Category A procedure because of the GS/DGPS requirement).
With respect to the issue of airspeed in excess of GS, the effects will always be beneficial because lower wind-speed is the limiting case. Although this does affect the continued take-off manoeuvre (ground speed up to 15kts, and groundspeed above 15 kts – what about the 15 kts case?), it is not of sufficient import to worry about.
I used to be of the same opinion as you with respect to the requirement for a Category A take-off mass – i.e. there is a WAT graph for each of the Category A procedures. However, the reason that there is a requirement for a Category A WAT in the ‘limitations’ section is because, even for a helicopter that is certificated in Category A, there is no compulsion to take-off or land within a Category A procedure. A good example of this is the offshore regime where Performance Class 2 is the requirement; however, this still has to be flown in compliance with the Category A take-off/landing mass.
There is also the case of the helicopter with more than 10 seats but not above the 9,072 kg (20,000 lbs) threshold (29.1(e)), for which only the basic Category A WAT is required. (Because the H-V Diagram (29.1517) is also mandated, the requirement aligns almost exactly with the Pure Performance Class 2 definition.)
The Category A mass limitation consists of a basic structural limitation (the MCTOM) and one that is associated with 29.67(a)(2) (the second segment climb) for all altitudes and temperatures specified in the approval. Yes, there are WAT curves in the Category A section, each associated with a set of procedures and the required profile, but these procedures/profiles are not always able to be flown (they might be unnecessarily limiting to the take-off/landing mass or the take-off/landing site might lack the facilities of a Performance Class 1 FATO). Yes, the graphs that show compliance with 29.67(a)(2)* are in the performance (information) section of the RFM but that does not show compliance with 29.1519.
* In fact there are two 'types' of WAT (four when anti-ice is taken into account): that for 2 min. OEI; and that for MCP OEI. Only the MCP OEI is required for compliance with the rule.
RFM that are approved by the Rotorcraft Directorate of the FAA have the Category A WAT in the limitations section.
Jim