Downwind.Maddi-Land
Thank you for posting that source material included in which is the circumstance in which HUD is not required for LTSC 1. It seemed to me however that SEN operations could not meet the requirement: -
"autocoupled to an autoland that needs to be approved for CAT 3A operations." (SPA.LVO.110 General Operation Requirements 2)
As we know, the SEN runways cannot be approved for Cat 3A and for reasons not connected with the ILS performance. Additionally RW05 has a 3.5 degree glideslope, which is outside the certification parameters for a Cat 3 ILS. On that basis SEN would not be exempted from the HUD requirement..
Your view that it only needs the ILS signal to be of Cat 3A standard is an interesting one. To my mind it doesn't seem to be supported by the wording of the above rule and I am curious as to whether your "inter alia" sources give a different slant.
Expressflight
My observation on RVR values was based on research published in the early days of autoland by either the Blind Landing Experimental Unit or BEA's AWOPS team (Can't remember which). It was statistically based then, I have always found it to be broadly accurate in the UK and it is interesting see your own SEN observations reach a similar conclusion nearly 50 years later. At the time it lead to the conclusion that Cat 2 was not very useful in the UK scenario and that airports and airlines should go straight to Cat 3 wherever possible.
As an open question, can anyone tell us the present AOM used by EasyJet at SEN, and whether Cat 1 autoland is authorised ?