PPRuNe Forums - VOR DME Approach

PPRuNe Forums (https://www.pprune.org/)

- Tech Log (https://www.pprune.org/tech-log-15/)

- - VOR DME Approach (https://www.pprune.org/tech-log/646127-vor-dme-approach.html)

SWH, all that is irrelevant because it doesn't explain why there are 3 different MDAs on that approach.

Wow, what a thread about a single Jepp approach plate! I agree with the comments above that publishing multiple MDAs depending on which stepdown fixes are used is more than unusual and non standard. Jeppesen just copied the AIP info verbatim, as they unfortunately often do - just for perspective: The corresponding chart from Lido just mentions one MDA, of course the lowest, and in the profile view shows the stepdown fixes as per usual.

And I suspect there is a lot of over thinking going on here. The most likely reason, IMHO, is that the AIP MDAs have not been changed from when the stepdowns were either crossing radials from another beacon or markers, i.e. before the advent of DME!

Quote:

Originally Posted by Capn Bloggs (Post 11217334)

SWH, all that is irrelevant because it doesn't explain why there are 3 different MDAs on that approach.

That is just the way Jepp publishes step down fixes inside the FAF, other chart providers only list one MDA. This isn’t the best chart Jepp has done, other providers have Trombay Hill clearly shown on the approach path with a MSA of 2100” shown to the left and below the 3.8 BBB waypoint. It’s a big feature that you fly close to, the Jepp chart gives the impression that it is flat terrain with just one mast.
in the FMC the coding is
FD32 +2600 -3.3
38VOR +1330 -3.3
28VOR +980 -3.3
MD32 350

almost.

The AIP chart posted at #32 by Bloggs (2019 edition) has 3 OCA(H)s. Jeppesen only follows that and Lido gents as well.

https://cimg0.ibsrv.net/gimg/pprune....81074eb35c.png

There is no hidden magic. Why the step-down fixes are there nor what is their effect on MDA and the purpose they serve.

Why the regulator chose to publish the 3 OCA(H)s is the unknown. The first OCA of 1330 can certainly do without (not the SDF, the OCA before it). It's overengineered

Which could lay a foundation for sub-optimal ARINC 424 coding as the database specialist has no way of second-guessing the intention behind an element which is unnecessary from the outset. Then you get various fuzzy / quirky interpretations by onboard installation. Last comes the contemporary pilot who was trained FMS = RNAV = GOOD = NOT MODIFY (does not remember anything more or care, other practical experience largely absent or well-forgotten) and ATTEMPTS to make ad-hoc procedures to tie all the loose ends which are not part of the problem itself.

You've seen it before too.