Its my understanding that the PANS-OPS requirements (#20) are directed more towards non-precision procedures and the obstacle clearance surfaces, i.e. the airfield environment. The aircraft height loss requirement may be demonstrated or calculated, but in my (dated) experience it might also be waved, particularly in the light of the VNAV / MDA height loss debates (N.B. TERPS may differ).
As an example an aircraft could fly a 5 deg non-precision approach segment, i.e. not landing straight in, without additional clearance (ht loss might apply). However, a 5 deg ILS approach and landing would require special aircraft clearance/certification.
Many years ago the basis for steep approaches was the Canadian (possibly FAA) ‘STOL’ criteria; IIRC this became a draft JAR 25 for aircraft certification. Does anyone have a reference for the current JAR/CS aircraft handling certification requirements, assuming that the draft was adopted, as opposed to using special conditions as per #19?
As a point of interest, back on thread, MLS systems were evaluated with very shallow glide paths to assess their capability of detecting aircraft flying below a nominal glide path. IIRC angles as low as 1.5 deg (obstacles permitting) provided much better warning ability that an ILS display.