G, memory fades, but subject to that; …
Flap 33 takeoff was initially a RJ100 modification requested by CrossAir for use at LCY. They wished to retain their full silver service galley load!
Subsequently the mod was offered for general issue, and I thought it could be applied to all 146/RJ variants, I have no knowledge of this other than for the RJ100. Check the ex Air UK 146-300s?
I don’t know how much a retrofit costs; it basically changes the takeoff config warning logic, and ensures the integrity of the landing config warnings. There is a switch/annunciator which (automatically?) resets after takeoff.
I don’t have the performance figures, but the aim was to ensure that the max RJ85 performance was achievable by the RJ100 on the original LCY 1100m runway (also with the same/acceptable noise footprint) for the same pax load. IIRC the RJ100 was slightly better getting off the runway but fairly obviously not in the climb.
The steep approach mod was a ‘standard’ retrofit/option which applied to all aircraft variants. The flight deck switch annunciator adjusted the EGPWS warning logic (available within the EGPWS) – basically doubling the approach slope capability. The selection resets automatically after landing.
Either with this mod, or as a separate package, there was a performance benefit applied by AFM amendment (it was ridiculously expensive - cost recovery objective). The LDR was adjusted by the geometric effects of a steep approach, the use of a 35 ft screen for landing, and a further benefit based on actual landing data. Because all of the standard RJ landing data was flight tested from a steep approach, the shortened flare path distance was claimed for steep approach operations. The overall benefit varies with aircraft series.
I don’t recall any handling issues. Steep approaches require the aircraft to be fully configured before the precision approach (ILS/PAPI). The max glideslope varies with aircraft type, 5 kt tail wind limit, no tailwind for the -300/RJ100 and 5.5 deg max; which are very sensible for such operations.
Autoflight systems were either self-adapting or used the switch input. Cat 1 limits were retained. But some authorities (illogically) increased the vis requirement – the over nose view improves with descent angle.
3 eng approaches / GA were authorised, but obviously not for takeoff.