...and a finally:
Requirement for, and use of, applicable heliport information/data
It is only possible to take off in PC1 from a heliport when the following are known and/or accounted for (or standard company procedures assuring obstacle clearance is in place):
1. For a runway procedure: the rejected distance, continued take-off distance (which may, or may not, include a clearway), and take-off climb slope;
2. For other procedures (including one within a limited area): the size of the helipad surface (TLOF) and area (FATO) for rejected take-off and OEI landing, the elevation of the take-off climb slope and length of the clearway.
Whatever profile is used, sufficient space must be available to allow the rotorcraft to accelerate from TDP to Vtoss prior to commencing the climb. For 2. above, this will inevitably require a vertical procedure where completion of the acceleration to Vtoss is conducted outside the boundary of the heliport - in most cases over obstacles.
In order for the pilot to ensure that the min-dip remains (the required height) above obstacles in the continued take-off, the provision of an elevated clearway is necessary. This provides a level datum for establishing the height of the TDP and length sufficient to allow completion of the acceleration to Vtoss.
The required procedure will be found in the Category A supplement; the procedure WAT may not meet the required climb gradient (normally 4.5%), even for the runway/clear area, and it may be necessary to establish (with the use of the climb gradient graphs) the gradient in the continued take-off (or balked landing). This may require a reduction in take-off mass.
Almost all modern helicopters provide a suite of Category A (vertical) procedures; most can achieve take-off at a practical operating mass meeting the required gradient[1] even when the clearway is elevated to a substantial height above the take-off surface (to raise it, and the take-off climb surface, above all obstacles). Power reserve provided by the 30-second and 2-minute settings (or 2.5 minutes if no 30-second setting is stipulated) can provide access to heliports (and required climb performance) in even the most complex obstacle environment (i.e. city centres with high-rise buildings).
[1] Some Category A Supplements now include a single gradient flown at one speed instead of two – this will be lower than the Vy, and might even be at Vtoss utilizing the 2.5-minute setting. There will be a precautionary note to the procedure to ensure that, before the limit is reached, a level acceleration segment has been accommodated.
Establishing minimum dimensions when in doubt (see also Appendix C to Chapter 3 of ICAO Doc 9261, Part 1)
The Rejected Take-off Distance (RTOD) in the RFM or Category A supplement (runway/clear area)
For most clear area procedures, the RTOD with complete helicopter containment will be provided in the Category A Supplement. However, that is not always the case, and it may be necessary to check that containment is in accordance with the certification specifications.
A reasonable pointer to the presence of doubt is when the drawing in the RFM does not appear to cover the front part of the rotor and rear part of the helicopter; the indicative drawing appears only to show distance with respect to a reference point on the helicopter; or, another term is used instead of RTOD.
When the RTOD with complete containment is not provided, adding 1 x Design D to the RFM dimension should provide a dimension that includes containment.
The absence of RTOD for the short-field procedure
RTOD is not a term that is usually associated with the short field procedure. Any number of alternative terms may be in use – none of which is likely to have a meaning in regulatory language. In the absence of certainty, adding 1 x Design D to the RFM dimension will provide a FATO that ensures complete helicopter containment.
The absence of RTOD for the helipad procedure
RTOD is a term that is almost never seen in the RFM for the helipad procedure. The term that is most often used is ‘the minimum elevated heliport size demonstrated’ (or another term approximating that meaning). This term indicates that the dimension of the surface area (together with the necessary visual cues)
only has been demonstrated and provided.
It may not be easy to establish the limiting dimension unless the heliport designer (or relevant subject matter expert) has surveyed, or is familiar with, all types that are likely to use the heliport. It would be wrong to assume that the declared dimension for a large helicopter will be greater than that for a smaller one.
When the limiting dimension has been established, if it is based upon ‘the minimum elevated heliport size demonstrated’, adding 1 x Design D will provide a FATO that ensures complete helicopter containment.