And what happens with the so called steep approaches? i.e. EGLC has GS 5.5º, or ENTC has GS 4.0º...
I've been trying to find a good definition of what you should consider as a steep approach without any luck. I just found on the brand new EU OPS that you have to establish procedures and get some kind of approval from the authorities for glide slopes > 4.5º. But once again, there is no definition available, unless you consider that if they speak for approvals if the GS > 4.5º, then no approval is required for GS < 4.5º...
But aircarft and crew qualification is required if you intend to use ENTC ILS to rwy 01 due to the steep angle!!!! What happens with those GS between that "standard" of 3º and 4.5º?
From an
aircraft certification point of view, the threshold values for GS are 3.5 degrees and 4.5 degrees.
Below 3.5 degrees are considered "normal" approaches and the standard certification testing set out in, for example, AC25-7A, and the standard regulations in Part 25 (or whatever) are consider to apply and be sufficient.
Between 3.5 and 4.5 are considered to be "increased glideslope" approaches. For approval of an aircraft to conduct these approaches at an aircraft certification level, Transport Canada has a "Working Note" (I think it's #12, but I'll stand to be corrected there) which specifies certain avionics tests be performed. However, it is assumed that the basic handling and performance3 approval is adequate - unless the OEM is trying to claim credit for the steeper GS in some fashion (usually landing "air distance" or dispersion) in which case corresponding handling or performance tests are required.
Above 4.5 is considered a "steep approach"; the rules here are imposed by "Special Condition" on an aircraft - by - aircraft basis - generally a new Special Condition starts with the last one and makes minor changes if required. So there are an informal set of rules, but technically there is no standard rule. A full set of handling and performance trials are generally required, in addition to avionics type testing.