The link Alexandre points to in his penultimate post show Dino Paggi explaining the Leonardo solution to the problem mentioned above:
The largest problem with the Category A procedures is the level acceleration segment at 200ft (from Vtoss to Vy) which halts the climb and, in a number of cases, drives the helicopter into the take-off OLS. However, these small and medium twins have the ability with a power-unit failure at TDP, to reach 1000ft within the 2.5 minutes. Manufacturers have become aware of this and are now providing modified profiles that do not require a level climb at 200 ft above the take-off point (or the TDP when that is in excess of 200 ft).
Aibus have chosen a different solution of a more limited nature as those who fly the AH145 will note; Bell have provided an alternative for the B429.
As Dino points out in his very clear presentation, it is not just the basic limitations (first and second segment climb) that have to be applied, the profile has to be adapted to address the obstacle environment of the heliport. This is more of an issue with helipad or short field heliports than runway-type sites.
For most heliports the take-off OLS starts at the end of the rejected take-off area (usually the FATO - which may be no larger than 1.5D); at the inner edge of the take-off OLS the helicopter must at 35ft and have met the requirement of the take-off distance required (TODRH - i.e. Vtoss and positive rate of climb). Dino does not consider this in his presentation - showing a marker at 35ft on the departure curve or, in a later slide, as being over a clear surface.
In Dinos's slides, all of the area below the helicopter up to the point that TODRH is reached is actually a clearway - declared by the heliport, or not (a virtual clearway). A clearway permits the convertion of potential energy (the height at the TDP) to kinetic energy (speed of the helicopter) by descending and accelerating to the TODRH. What is provided by the manufactuers in their performance data, is the distance to the TODRH (from the TDP or back of the FATO) and the drop-down (from the TDP to the min-dip - shown on Dino's slide as 15ft above the surface) but not the distance of the min-dip from either of the two reference points; the PC1 take-off OLS (slope from the end of the FATO/clearway) is not considered. (In the manufacturers world, the surface is regarded as flat but with obstacles.)
For the heliport designer, increasing the PC1 take-off OLS to greater than the current 4.5% (approximately 2.57 degrees) to clear obstacles is not really an option; neither is providing an obstacle free clearway on the surface. The solution is to elevate the origin of the OLS to a point where it clears all obstacles along its length (which may be curved) and provide a virtual clearway. This clearway, of a distance required by the design helicopter, commences directly above the outer edge of the FATO/rejected take-off area and intercepts the (elevated) OLS at the required distance. The origin of the take-off surface is then regarded as being displaced to the outer edge of the clearway at the height of the clearway. The details of the clearway - its height and length, and the origin of the take-off OLS should be promulgated in the heliport data.
The pilot now knows the height of the surface (the clearway) above which the TDP has to be provided (so the distance to the mon-dip is not an issue) and the distance to the take-off distance available (the commencement of the, displaced, take-off surface).
This solution is not just confined to the heliport designer, it also permits an operator to provide similar data at any heliport to which operations are considered (for example a heliport at a hospital). To avoid unecessary calculations, a virtual clearway of 300m could be used; most helicopter will be able to use this. As the height of the TDP increases, the required clearway distance decreases (unless the vertical procedure is a true vertical one i.e. as for the AH145, for which it remains constant).
The gist of this can be seen in the following presentation that uses the relocation of Addenbrookes helipad as an example.
https://www.dropbox.com/s/i5am5zyg5a...sion.pptx?dl=0
It is a pity that Alexandre has reached his temporary limit of seven posts; however, deleting the thread is not the solution to this as it negates the contribution of others.