hold the phone...
As we all know the 2.5% Jep OCA figures aren't based on s/e BUT then, why isn't the s/e overshoot taken into account.
How do you suggest that we do that? What baseline aircraft type should we use, in determining an appropriate OEI missed approach climb gradient? It's an impossibility because we, as designers, don't know :-
1. WHERE, in the procedure, the failure will occur; and
2. WHAT nett climb gradient will be appropriate.
The protection area would be so broad that the DA/MDA would be completely useless. The 2.5% basis is just that, a basis. What you are being told on that HK approach chart is that, if YOUR aircraft cannot climb at the higher gradient,
for any reason at all, you must either use the higher DA/MDA based on the lower climb gradient, or have already done your own performance appraisal and set a DA/MDA that will be safe for YOUR operation.
Some airlines employ people to do that, others contract the work out to somebody else. Some MIGHT just bury their heads in the sand. I hope, for your sake, that your company isn't in the latter group.
It IS legitimate for a procedure designer to apply a non-standard missed approach gradient, where necessary, to achieve the lowest possible DA/MDA. Pans Ops says we can go up to 5% without industry consultation. The steeper climb gradients recognise that advances in aircraft performance mean that some aircraft types can take good advantage of it, while others cannot.
That is a fact of life.
It also needs to be said that Pans Ops (and probably TERPS as well) regards the missed approach as an emergency situation. That is to say, a situation that should not arise frequently and, therefore, the actual risk associated with the use of it should be minimal. This is why you are given so much less obstacle clearance in the missed approach, compared with the various segments of the approach itself.
I'm not going to enter an argument about the rightness or otherwise of the philosophy of an "emergency situation", I am merely stating the fact. I suspect that what you are really after is the fruits of the performance assessment work that has undoubtedly been done for or by Dragonair, Air Macau, etc. They will have paid a LOT of money for that assessment, so they won't be willing to give it to anyone - that's just a commercial reality.