Vidual,
I think the point that is important is contained in your first sentence:
Almost all these requirements that you mentioned are already fulfilled...
The explanation for why PC2e and not Category A is fully explained in Chapter 3.2.4.4 of Doc 10110 (to which you have provided a reference). Here are a couple of extracts:
‘Performance Class 2 enhanced’ (PC2e) is where exposure is present only for a small percentage of flights – i.e. when the helideck environment prevents engine-failure accountability. It requires performance with deck-edge miss and continued flight* following an engine failure on take-off or landing without meeting Category A criteria.
* In the case where flights are being conducted in conditions of low wind and calm seas, operating in ‘pure performance class 2’ would permit a greater take-off mass than PC2e. This would be subject to ‘deck-edge clearance’ assurance and acceptance by the customer that a safe forced landing (ditching) is an acceptable outcome to an engine failure during take-off.
Category A elevated helideck procedures establish profiles and masses (adjusted for wind, temperature and pressure) which assure a 15 ft deck edge clearance on take-off and landing; drop-down must be calculated and, once clear of the helideck, a helicopter operating in PC1 would be expected to meet the 10.7m (35 ft) obstacle clearance (from the sea).
These procedures and clearances can be assured only when: the helideck is of the required size; the take-off or landing is oriented into the obstacle free sector* (OFS); and, the profile is flown as defined. Because these conditions cannot always be fulfilled in offshore operations, a prescriptive regulation requiring operation in PC1 is not regarded as practical (OEI HOGE could be employed but this would result in a severe and unwarranted restriction on payload/range).
* For offshore helidecks, the Obstacle Free Sector (OFS) should extend through a minimum of 210⁰. This consists of a surface clear of obstacles, out to a specified distance, at the helideck level - within which is a 180⁰ arc that is free of obstacles down to sea level (see Annex 14, Volume II, Figures 4-7 and 4-8).
PC2e mass calculation provides notional* performance. Actual performance is dependent upon:
- accuracy of the calculation;
- how close actual conditions are to those planned;
- whether the optimum profile can be flown; and,
- the orientation of the take-off and landing with respect to the OFS.
Planned obstacle clearances should be achieved when the defined profile is flown, and take-off or landing is directly within the OFS; if these conditions cannot be met, exposure might be present**.
* Notional because of the assumption that: the profile is defined and oriented into the OFS; the deck height above sea level is constant; and, the procedure is flown as published.
** Although exposure may only be present for a very small proportion of arrivals/departures, the requirement for PC2e should be contained within a variation that permits exposure.
The text goes on to provide example of when these assurance cannot be met (not shown here). It then continues:
Under these, and other, circumstances, the Commander might adjust the profiles to address a hazard more serious, or more likely, than that presented by an engine failure; regardless of these issues, the calculation of mass should still remain as defined in above.
Because of these, and other (unforeseen) circumstances, a prescriptive requirement for PC2e obstacle clearance cannot be applied*. However, a target of 15 ft deck-edge, and 10.7 m (35 ft) obstacle, clearance should, where possible, be considered.
* If the requirement for PC2e is stated as an objective within a Code of Performance, the method(s) of compliance should specify how the ‘notional’ take-off/landing mass is calculated.
The basis for provision of procedures in Part 2 of the RFMs is provided on the last clause of the referenced text:
This [ed. the procedure]
will require manufacturers’ information reflecting these elements. It is expected that such information will be produced by utilising performance modelling/simulation using a model validated through limited flight testing.
The flight testing of a category A procedure is complicated and very expensive - when it is known that it will only be used in principle. It is understood that, for PC2e, manufacturers use their library of flight test data to stitch together a profile (procedure) and then model the outcome to establish it meets the specified clearances. The procedure is put into Part 2 of the RFM which does not require approval by the certificating authority. Although the procedure may well satisfy all the elements of a category A procedure, it cannot be regarded as such.
As this response is getting long, I'll pause and move on to the other points in the next post.