Historical note...
PVD's were used (to the best of my knowledge) on only one civil American type, a Gulfstream One aircraft, owned and flown at the time by the radio and television personality...Arthur Godfrey.
With this aircraft, CATIIIA hand flown approaches were FAA approved, circa 1960.
The PVD's were certified and provided by the Collins Radio Corporation.
Having used the PVD in TriStar equipment (ex-BA aircraft)...they worked to perfection.
Full marks for the designers of the HS.121 Trident aircraft...they provided CATIII autoland when others couldn't/would't/didn't.
A superb achievement.