DB has not gone quiet....he was thinking.
And a pretty big thinks bubble it was too - good stuff though!
Just a couple of points:
1) as far as I know they were not coming in off an ARA, they made an en-route descent (or at least not a normal ARA), so your points about the ARA minima, whilst maybe valid, are not relevant to this accident.
2) We in BHL have something like your gate in with specified parameters, to run in at until we see the helideck ovality indicating the correct site picture. It certainly empowers PNF to intervene early if you go off the parameters.
3) Be careful not to specify too high a minimum height for the level sector. In an automated aircraft, its all fine and dandy whilst you are running in coupled, the trouble starts when you decouple and fly manually. The higher you are, the further out you are and so the smaller the installation is. At 400' going into a ship with a 50' deck, that's getting on to being too high IMHO. In a 225 its better to be lower and slower coupled, that way when you decouple, the helideck is getting fairly big and visual references are better. I would prefer deck height + 200 for all approaches - keeps the scary bit where its being flown manually to a minimum!
4) If you make me say "call the ball" I shall stop liking you
HC