... and to continue the point:
Provision of data on the size of the required surfaces/areas.
The certification of performance procedures/profiles is normally conducted on aerodromes with runways that are extensive in terms of space and visual cues – particularly peripheral cues. Whilst ideal for the provision of data for runway/clear-area procedures and climb data, it has its disadvantages when used for testing and certification of vertical procedures.
When used for the runway/clear-area procedure, the resulting graphs can be used to apply the data to the location or, alternately, to use the location information to modify the mass and distances. In general, the guidance uses standard language constructs to describe surface conditions and boundaries when meeting the certification objectives. There may be minor issues with helicopter containment but, in general, if the applicant applies the guidance correctly that will not be the case (more on this later).
For those procedures/profiles where the eventual usage will be in limited areas bounded by space (elevated or ground level helipads) or obstacles (areas in obstacle-rich areas, where helicopters are at their most effective) the absence of guidance on the helipad dimension providing both: a surface on which the touchdown takes place; and, containment of the whole helicopter when it comes to rest from a rejected take-off (which represents the full embodiment of the take-off distance required), or OEI landing, was, and remains, problematical.
In the case of a vertical procedure where the AEO departure, rejected take-off and OEI landing all use the ascent/descent surface, these dimensions will be identical for both types of touchdown.
The size of the required surface(s) will have been established from a series of dots (located from a reference point on the helicopter - one for each touchdown) on a scatter graph generated from real-time rejected take-offs, or OEI landings, and under controlled flight test conditions. The scatter graph will be used to define the minimum size of the required surface area. However, unless this data is based on manoeuvres, from multiple directions to a surface which is representative of a heliport with the ICAO Standard (FATO, TLOF and TDPM) markings, the resulting dimension may not be matched to the operational context in which it is to be used.
Where the Final Approach and Take-Off (FATO) is the area within which, at the termination of a normal or abnormal approach, the design helicopter will be (completely) contained (which may extend beyond the physical surface of an elevated helipad); Touchdown and Lift-Off (TLOF) is the surface within which, the undercarriage will be (completely) contained; and, Touchdown and Position Marking (TDPM) are those aiming and touchdown markings described in ICAO Heliport Manual (normally, a circle with a diameter of 0.5 x maximum length of the design helicopter – which yield the minimum possible overall dimensions), for use on heliports, helipads and helidecks in most regulatory regions. Because of the necessity for visual cueing during OEI landings, the TLOF (undercarriage containment surface) might be as large as the FATO (helicopter containment area).
The use of an area on the runway that does not have the standard ICAO standard helipad markings can therefore result in issues both of size and, in the case of use on an elevated helipad, required visual cues.
Use of the certification minimum climb performance to establish the WAT graph
When meeting the minimum certification standard, an operator does not show anything other than compliance with the limitations of the RFM. The WAT is a nomogram format graph, that defines the maximum mass for the procedure to which it is applicable and includes climb data to achieve the minimum performance Category A standard. It will satisfy all critical elements of the profile (i.e. reject ROD, conversion to level flight from the TDP, and distance to TODR) but is not applicable to any known obstacle environment or departure slope - it is performance in a semantic bubble. This is not just the case for vertical procedures/profiles, it also applies to the runway/clear-area procedure.
Depending on the speed(s) specified for the type/procedure, the minimum required performance for the first segment might only provide a climb gradient of 1.6% or 0.9°- which is almost indistinguishable from level flight. Minimum performance in the second segment is almost the same at 1.8% or 1.06°. The shallowest available slope at a PC1 heliport is 4.5% or 2.58°.
It is the State’s regulation that defines the operational standards for approach, departure, and en-route performance – (normally) in conformance with a Code of Performance. This along with the aerodrome/heliport information will determine the required climb gradient and obstacle clearance to meet the operational objective.