During the middle part of this thread, there was a discussion on the graphs and other data included in the Category A Supplements. Given that discussion, and after a conversation with a friend with more knowledge than I could ever have, the following is offered in explanation of the process of producing, and the contents of, those Supplements.
Hopefully, others will take the opportunity to add their comments and experiences.
Exploring Category A design and testing and the contents of the Category A Supplement
The design, development, testing and certification of a Category A procedure – other than the clear area/runway, which is a basic element of Category A certification, is an expensive undertaking for which recovery of cost can be achieved only through the sale of aircraft. It results from an operational requirement that is either part of the perceived role of a type (such as air ambulance in the case of the small and medium twins) or, as a request from an important user group (such as the oil companies in the case of offshore operations).
The design and testing process
The design and testing process for each of the procedures, although specific to each manufacturer, would follow a similar path. The example below starts with the establishment of the basic elements of Category A Performance before progressing to the definition of a clear area/runway, and Vertical, Procedure.
1. First, all of the trim flight performance testing (hover, level flight, climb and descent) is carried out in fully instrumented helicopters and ideal conditions. Parametric power required data maps and a trim flight performance computer model are developed.
2. Engine inlet and exhaust surveys and installed engine power available verification testing are carried out, and the installed engine power available computer model is obtained from the engine manufacturer.
3. The Category A second segment WAT curve is then calculated using the results of 1 and 2. Note that the Category A second segment WAT curve gives the absolute maximum possible Category A weight for altitude and temperature.
4. The lowest Vtoss at which the Category A first segment WAT curve, at least equal to the Category A second segment WAT curve, is determined using the results of 1 and 2.
5. The Category A airfield procedure is developed by flight testing at the WAT curve determined in step 3. using Vtoss from step 4.
6. Category A first segment WAT curves are then calculated for reduced Vtoss values using the results of 1 and 2. Note that these result in lower weights when adjusted for altitude and temperature.
7. The airfield Category A field length data maps are then developed by flight testing at WAT limiting conditions for all selectable Vtoss values.
8. While the airfield WAT curves are based on trim OEI climb performance minima, vertical procedure WAT curves are based on low-speed dynamic performance - that is, the ability to transition from AEO flight at TDP to OEI flight at Vtoss, or from AEO flight at TDP to OEI for a reject.
9. Low-speed dynamic performance data are acquired during vertical climb and descent, and OEI
[1] reject and flyaway, with engine failures occurring over a wide range of weights, TDP heights, and Vtoss values. These data are used to align a Low-Speed Dynamic Performance computer model.
10. A Vertical Procedure WAT curve is calculated using the correlated computer model (mentioned above) and compared with the Category A first segment WAT curve - to confirm that first segment OEI climb performance minima are also achievable.
11. The final WAT curve is validated by conducting OEI reject and flyaway tests at WAT limiting conditions over the established range of TDP heights and Vtoss values.
12. While the above addresses the take-off case, the Category A airfield and Vertical Procedure landing procedures are developed similarly.
13. The final procedures are reproduced in the RFM and observed, or flown, by the authority test pilots during the acceptance and certification process.
Where appropriate, nomogram format charts are used to present multivariate performance information on a single RFM page. Rate of Climb (ROC), which is a function of engine power, mass, altitude, temperature, and airspeed, is typically presented using a nomogram format chart. ROC charts are constructed by first calculating the ROC for specific engine power ratings and airspeeds at many discrete points over the range of mass, altitudes, and temperatures that define the operating envelope of the helicopter. With the use of regression analyses, the resulting data are correlated and compressed into nomogram format charts. This technique is also used to construct the take-off and landing WAT curves as a function of Vtoss.
Contents of the Category A Supplement
The Category A Supplement is contained in the Approved Section of the RFM; it contains one, or all, of the Category A procedures
[2] that are required to ensure that the helicopter is capable of meeting its full potential (note that in some manuals the clear area/runway procedure is contained in the basic part of the RFM along with the Category A WAT and performance data). The contents would normally consist of:
A general part that includes: terminology and definitions; useful information about the choice of a procedure; limitations and general performance data, all of which apply to any/all of the approved procedures.
A number of individual parts, each applicable to a specific procedure containing: limitations; normal procedures (including diagrams and pictures); emergency and malfunction procedures; and performance data.
Flight profile diagrams, FOV pictures and, with the use of relevant examples step-by-step instructions to the pilot for using the graphs and data for establishing the required parameters and distances to match the profile to the heliport data, are provided. The pilots required actions during normal, malfunction and emergency procedures are described in detail. Flight outside the relevant WAT or flight profile invalidates the procedure and could, in the event of an engine failure, result in other than a safe landing or continued flight.
Vertical Procedures rely upon the accurate determination of mass and, during the piloting phase, precise control of: power - through control of rotor speed (Nr); attitude; and height. Whilst failure to apply the procedure as defined might not result in unforeseen consequences, there are critical points in the procedure/profile where the risk is greatest and at which testing has been concentrated. These are the (pre-determined) intervention time immediately preceding TDP and LDP. As the profile tends away from those points, the risk lessens, and the consequences of an engine failure diminish; however, that should not be seen as an opportunity for casual observance of the sequence, parameters, or limitations of the procedure - the responsibility for occupants and third parties rests on the shoulders of the pilot(s).
[1] To avoid employing the 0EI, 30-second setting with its potential for destructive consequences during flight testing, the power, or the total aircraft torque, may be artificially limited by using a specially adapted FADEC mode (as it currently is for pilot training). This can then be compared to the engine power available in the provision of the WAT graph.
[2] This does not include any procedures that have been developed to satisfy an operational regulation, request, or requirement and are contained in the non-approved section.