This is realy a very interesting issue to discuss and to try to obtain a correct answer which is not easy, as we can see.
Nevertheless let me introduce a couple of things for reflection.
1- When operating the aircraft (twin engine for instances) am I realy obliged to comply with the restrictions of FAR25 (or JAR/CS25)? Or this is a matter for the constructor when applying for certification of an aircraft model? Do I realy have to make sure that 2.1 % of climb gradient in AppClimb phase is being obtained? This is FAR 25.
Take a look on FAR 25 initial point:
Sec. 25.1
Applicability.
(a) This part prescribes airworthiness standards for the issue of type certificates, and changes to those certificates, for transport category airplanes.
(b) Each person who applies under Part 21 [New] for such a certificate or change must show compliance with the applicable requirements in this part.
2- If I am operating the aircraft (as a pilot or "Operator"-company) my "rules" are the JAR/EUOPS-1 or FAR 121/135/91. Right or wrong?
JAROPS1 states:
JAR–OPS 1.485 General
(a) An operator shall ensure that, for determining compliance with the requirements of this Subpart, the approved performance data in the Aeroplane Flight Manual is supplemented as necessary with other data acceptable to the Authority if the approved performance Data in the Aeroplane Flight Manual is insufficient in respect of items such as:
(1) Accounting for reasonably expected adverse operating conditions such as take-off and landing on contaminated runways; and
(2) Consideration of engine failure in all
flight phases.
FAA stated in PART 121:
Sec. 121.141
Airplane flight manual.
(a) Each certificate holder shall keep a current approved airplane flight manual for each type of airplane that it operates except for nontransport category airplanes certificated before January 1, 1965.
(b) In each airplane required to have an airplane flight manual in paragraph (a) of this section, the certificate holder shall carry either the manual required by Sec. 121.133, if it contains the information required for the applicable flight manual and this information is clearly identified as flight manual requirements, or an approved Airplane Manual. If the certificate holder elects to carry the manual required by Sec. 121.133, the certificate holder may revise the operating procedures sections and modify the presentation of performance data from the applicable flight manual if the revised operating procedures and modified performance date presentation are--
(1) Approved by the Administrator; and
(2) Clearly identified as airplane flight manual requirements.
Amdt. 121-251, Eff. 1/19/96
For me, it looks like in an OEI situation, the performance that is in AFM might not be the one that we are looking for (because once again it is prepared for the Certification Standards).
3 - What about the 2.5% (or greater) in Missed Approach phase?
This a metter of another "rule" - ICAO Doc 8168 PANSOPS.
This is designed and prepared in the assumption that ALL ENGINES ARE OPERATIVE.
In this case, IF ANY DOUBT EXISTS IN OEI YOU (your company) SHOULD HAVE A CONTINGENCY PROCEDURE (MAY BE AWAY OF THE MISSED APP TRACKING).
Another way to look at it is that weather conditions might interfere in the DECISION PROCESS.
If in VMC why to think in Decision Altitude at 200 feet? You can decide earlier and "COMMITTED TO LAND" at a higher altitude (1000 feet AAL for instance).
In this case if any thing goes wrong and Go Around in OEI is initiated, you are well above the requirement of the Doc 8168 (or TERPs in your case).
Conclusion:
For me what is important is that I AM SAFE (SAFETY FIRST) but I AM OPERATIONAL (Commercial Pilot).
What is SAFE?
The industry says that "have to clear all obstacles by 35 feet (50 feet in turns greater than 15º)"
Which means, IF YOU YOU ARE IN A "NET" CLIMBING AND CLEAR ALL OBSTACLES (even Visually is contemplated) then you are SAFE.
This is legislation then, WE ARE LEGAL complying with it.
Remember that TERPS / PANSOPS design Missed Approach with obstacle clearances of 98 feet and 164 feet in intermediate phase WHICH ARE MUCH HIGHER THAN THE FAR 121 and EU OPS-1 (35 feet).
This is another view of the problem
Best Regards