Interestingly enough, some 17 years ago I was "loaned" (no doubt at great expense) by my company complete with an F/O to the FAA to spend 2 days in the 146 simulator at Hatfield. The idea was to see if it was possible to fly 7° approaches with any regularity.
The guy in the back was connected to the FAA computer in Kansas City and we were only given a few minutes warning of which approach we were to fly selected at random by the computer.
In other words, it might be a 3-engine approach flown with a go-around at IFR minima or a 4-engined approach at MLW with a full stop landing on a wet runway. We never knew what was coming next.
We used various critical airfields such as Casper, Wyoming, LCY, and Aspen, Colorado.
We were able to prove that a 7° glide slope is the absolute maximum that can be achieved by a BAe146 in still-air conditions. In order to achieve that, you have to be back at VRef+5, Gear Down, 33° Flap with the Airbrakes out and Power back to FI on G/S intercept otherwise it is impossible to stay on the G/S.
LCY was, I believe, originally looking at a 7° slope for noise abatement but such a notion was not practical for everyday purposes. That is one of the reasons why 5.5° was considered to be more practical.