Originally Posted by
Uplinker
@A320LGW;
Yes exactly; that's why I am suggesting it. With a NPA approach, you are heavily reliant on having set the correct QNH, and have no means of cross checking that you are on the correct profile - as you do with a ground transmitted glide-slope. Bear in mind it may be IMC, with absolutely no external visual references and a bad radio link in a noisy cockpit, with language issues. A surveyed series of Rad Alt heights, for, say, the last 4 miles* written on the NPA plate might be an easy way of providing that cross check, and allowing a safe go-around if something did not match up. Checking altitudes against distance to go on a NPA is useless if the QNH is set wrong, as this near CFIT has shown.
Even if a crew does monitor the Rad Alt, the terrain might not be flat, as you say, so the readings might be quite different from the altitudes - even if using QFE, so not always easy to decide if the Rad Alt figure is reasonable or not. Having a series of surveyed heights vs distances on the plate, might give improved reassurance?
*Or perhaps just one radio altimeter check height printed on the plate for the 4 nm point would serve as a gross error check?
Is the problem with this that, within the acceptable lateral tolerance of flying the approach, there could easily be e.g. a 200’ high building that you may or may not bounce your radalt off?