Geoffers,
I did a google before posting my last reply and most sources do refer to it as "automatic" although I did find one site with your suggestion (altitude). I did decide to go with "automatic" as other functions of AVAD (enhanced AVAD) are not altitude related. Maybe someone in the know can give us a definite answer?
Be careful - your radar should be placarded "NOT TO BE USED FOR NAVIGATIONAL PURPOSES'. Just because the UK CAA (and some others) chooses to allow such IFR techniques does not mean that they are acceptable in other countries.
Geoffers, are you suggesting that for once the CAA does allow something that others do not??? Whatever next .....
Even the JAA/EASA allow this procedure for CAT under JAR-OPS 3. In any case I would suggest, if done properly, it is a far safer approach in low visibility (see above).
Cheers,
Woolf