Originally Posted by
Don Coyote
Apparently it is down to a misunderstanding by the service providers who produce the charts. Because the minima is based on a continuous descent profile, they call the minima (under the new rules) a DA even though it is a non precision approach. For a non precision approach (under the new rules)you will still be unable to pass below the minima regardless of whether it is a MDA or DA; hence the requirement to add an amount appropriate to your aircraft (nominally 50')
With all due respect, I do suggest that you do not appreciate the full picture. The chart providers have very good understanding of regulatory changes in OPS procedures and that is why they correctly show DA for EU-OPS (appendix new to 1.430). As you correctly say, unless you are approved for such operations by local CAA you should not be using those charts.
If, on the other hand, you have the approval, there are two possible solutions. The classical approach/approval that you describe would have you add an increment (i.e. 50 ft) and treat NPA DA as an MDA and there is nothing wrong with that. Other possible approval will allow you to use DA with no additionals and operate with "decison" at DA (and duck under during go around) as opposed to classical "level off" at (M)DA. Extensive reading and good understanding of Doc 8148 both volume
I and II is required to find out that the obstacle distance on NPA with DA is in fact still greater than o.d. on an ILS with DA. And nobody disputes DA on ILS, we'll agree to that.
The previous requirement to avoid flight below MDA was based on the situation that you continue towards MAPt after reaching MDA. As long as your operator addition was 0 (common case) MDA = OCA or system minimum and flight below OCA clearly must be avoided. The
M.O.C. to calculate OCA on NPA is still greater than the
margin used for determine OCA for ILS approaches. Nowdays, level flight to MAPt is about to be prohibited. Ergo, you do not need to treat NPA OCH (or system minimum) as an MDA anymore because the level-off is not an option. So the only remaining problem is the go-around "duck under" called
height loss by 8168. The
margin for precision approaches allows for go around height loss and more. The
minimum obstacle clearance for NPA is greater than
margin and also is based on wider protection areas. With regard to obstacle distance (my generic term) a go around on a NPA DA (no additionals) is safer than GA on an ILS as was always the case - Doc 8168 vol I and II reveal. Hence the possibility to use DA for NPAs because level flight towards MAPt (which would put you below OCA and is clearly forbidden) is no longer an allowed manoeuvre.
Sincerely,
FD (the un-real)