Aircraft need to be specifically certified for "steep" approaches i.e. 4.5 degrees or greater.
There's currently no official standard regulation for this, and as a result it gets done on an ad hoc basis per type, with the authorities generating "Special Conditions" or "Certification Review Items" for that type detailing the specific requirements.
The following is taken from a statement by EASA on a recent such exercise...
The requirements covering Steep Approach have been under discussion for some years and NPA 25B-267 (Final Rule) dated March 1999 was the last iteration to receive full circulation and comment within the JAA. However, this version has not been published as a change to CS 25, to date, and experience during usage on several projects has produced additional comment. EASA proposes that the safety standard for evaluation of steep approaches should be based on NPA 25B-267 (Final Rule) dated March 1999 and include amendments as agreed for application on another recent EASA certification.
I'd have thought the first places to ask would be (1) the OEM (2) the original certifying authority and (3) your local certifying authority, if different.