I appreciate that the vast majority of responses here relate to the UK, but Boudreaux Bob has already given the Jepps decode which categorically rebuts the use of the rad alt, and my references are to my 'home ground' of Australia. As already mentioned, many ILS runways here have the surrounding land significantly
below the threshold height thus rendering a radalt reading unreliable at DA/MDA.
This is still an International Forum!
Originally Posted by
Pete O'Tewbe
Whilst PEC may indeed apply, I'm not sure that this is what is being discussed here. If you are applying a PEC of, say, 50 ft, what was a DA of 400 ft now becomes 450 ft. In any event, PEC does not apply to NPAs with a published MDA, at least in the UK.
Pete O'Tewbe, the use of PEC relates to whether one is published for the aircrat in use: the +50ft is applicable in Oz for aircraft that
do not have a published PEC. It is derived from the practicality that a published PEC will be of a low value, so 50ft is a reasonable impost on the lag of an baralt during a precision approach. If there is a PEC then you should apply that.
Have you ever checked whether
your aircraft has an approved PEC, and the ramifications if it doesn't?