Originally Posted by
Kerosene Kraut
Point is you will have to add some safety margin making the approach even steeper: Like in LCY it's 5.5 degrees plus 2 = 7.5 degrees that you need to be certified for. If you aim at 4 for noise abatement you'll end up close to six in real life certification. That is way steeper than many a/c can handle. There where quite a few mods done to the A318s computers, avionics, callouts, trim, flaps and speedbrakes in order to get it certified for LCY ops.
That bit in bold isn't quite right. As the certification rules are currently applied (and there is some variability between jurisdictions, and some of the rules are evolving as new aircraft apply) the rules are:
up to 3.5 degrees - nothing special required, standard certification applies (i.e. 3 deg G/S)
between 3.5 and 4.5 (4.49999999 if you like) - additional requirements for autopilot etc.; no additional requirements for SubPart B (i.e. performance and handling)
4.5 and above - considered "Steep Approach" - additional SubPart B requirements added, including the "+2 degrees" abuse case.
So certifying a 4 degree approach would typically require additional avionics work but generally not much in the way of handling and perf tests, and certainly not the 2 degree abuse case. (That's pretty much the TCCA/EASA approach right now, with the FAA not too dissimilar)