Re-reading this thread, I am reminded of the pair of USAF H-53's that were stuck in fog at Eglin AFB. They stopped at a 500 foot hover, IFR, over the field, using the auto-hover coupler, then simply dialed in progressively lower altitudes on the altitude set knob until they could see the ground! This was reported in the aviation press (Rotor and Wing, I think).
That certainly shows the ability of rotorcraft to perform 90 degree approach angles!
Xnr, call or email me on that Cat A stuff. Dave has had the good sense to retire!
Nick