"Further thought is that is predicating an approach on a barometric altimeter or ADC still valid? (Despite what Nav Canada would like us to beleive about Temperature Compensation). "
We are looking at normal Cat I ILS here, and the height loss values are those in ICAO PANS-OPS (Doc 8168) - NOT the FAA TERPS criteria. Better believe the temerature correction advised by Transport Canada, since they are supported by some very real evidence. Peter Foreman's (IFALPA) report of his discussion with a South American operator who lnaded before him and had a GPWS warning on a very cold day for one, and Don Batgeman's world tour in their instrumented King Air (one UK airport had an 800 ft error). Don Bateman is the engineer who invented the GPWS system. The error is based on the Off Standard atmosphere as defined by the Engneering Sciences Data Unit - it is the standard lapse rate shifted to the required colder temperature. It is recognized that the real lapse rate is often very different (inversions etc), but at least it will prevent some of the CFIT accidents!
"The majority of current Part 121 & 135 aircraft are going to use a radio altimeter below 2500 feet agl and, if an ILS is available, use a Decision Height (aka RADIO) not the BARO Minimum Descent Altitude."
You alarm me a little - For Cat II operations OK, and a radio altimeter OCA/H is normally promulgated. However, for Cat I it is an option but seldom promulgated, while for non-precision, never.
"Future aircraft with Wide Area Augementation System (WAAS) GPS will also not use a baro altimeter but derive it from the GPS for an LPV approach again with a Decision Height lower than the equivalent MDA."
Be sure you know just what is b eing promulgated - there are sites where the terrain in the approach is not suitable for radio altimeters!
Many thanks for your input, so far the best suggestion is the RVSM spec since it willcover those older aircraft that have the modern peizoelectric altimeters.
Robert