If the above two problems are addressed then you can fly a perfectly respectable approach
Nothing more respectable as the sight of ground from 500ft agl on NDB with 20G30 and heavy rain 
It’s in turbulences where NDB shine: you get tossed +/-30deg bank while the ADF needle is all over the place, good luck figuring out when you have gone past +/-5deg of the track !
Malibuflyer wrote:
Technically you are right. Practically not: While they can not establish a formal equipment requirement for airspace use, they can still structure it in a way, that only aircraft with the required equipment can actually use it. If they, e.g. define the usable IFR waypoints only in terms of NDB/DME (obviously absurd but theoretically possible), you can not legally plan a flight without carrying this equipment. At least today using the GPS overlay as a replacement would not be allowed.Luckily, the reality moves into the opposite direction: The vast majority of NDB-approaches got a small “(GPS)” in front of the NDB in the AIP and therefore are completely legal to fly in aircraft w/o ADF installed.
Essentially agree. May vary a bit depending on applicable law.
Under FAA regulations, GPS can be used to identify waypoints on any approach type. So any approach that has a locator or NDB or NDB/VOR/DME point-in-space to identify a fix (crossing fix, MAP, Hold, etc), then an ADF is not needed in the aircraft and GPS can be used instead. If an NDB approach does not have a GPS overlay (e.g. “(or GPS)” in the procedure name) then an ADF still legally needs to be available (installed and operational) for tracking the final approach, even if one decides to use GPS guidance instead.
Seems pretty sensible.
One of the EASA committee members posted this on a private site:
So, as more or less correctly identified in posts above, this substitution is basically worthless.
That new AMC that will come into force in NCO.IDE.A.195 is clearly worthless, useless and pretty much out of touch with anything about navigation inside the solar system
CAA went for ORS4 1472, that removes DME requirement until March 2022, then with a bold move into CAP1926
The thread on the UK CAP1926 is here. Not sure it is worth anything either, if you actually read that discussion.
I am writing this from vague memory and I know @ncyankee will correct me but I think the US went through 3 phases
Europe (and the UK in CAP1926) is still in the 1st phase.
Peter wrote:
So, as more or less correctly identified in posts above, this substitution is basically worthless.
Let me first say that I don’t agree with the AMC – I do find it too restrictive. But I don’t agree that it’s worthless. E.g. NDBs/VORs used as fixes in an instrument approach procedure can now be substituted by RNAV fixes. That would address the odd practise of the UK CAA of using NDBs in the missed approach part of RNP approach procedures. (Yes, I know this AMC doesn’t apply to the UK, but I understand the CAA has published very similar guidance.)
Anyway, there are reasons why the AMC is written the way it is and in a discussion you should be aware of the reasons.
First, no substitution for lateral guidance on final approach. I know it is hard to believe, but the theoretical accuracy of an NDB (and certainly a VOR) is in some cases better than the theoretical accuracy of LNAV. For the most common case of an NDB approach with the NDB located about 4 NM from the runway, there is a small area around the NDB itself where this happens. Apparently EASA didn’t want to open the can of worms it would involve to find out exactly what approaches would have significant obstacles in that area.
Secondly, no substitution for DME. There are safety issues with this in the general case, but there are many special cases where it would be perfectly safe – particularly the cases where a DME-based fix is co-located with an RNAV fix in the database. One safety issue is that on an instrument approach, the GPS box would show distance to the runway, but the DME need not be located at the threshold and it could also be offset. Another one is that the DME may have the same ID as a different navaid but not be co-located with it, so there is risk of selecting the wrong navaid from the database. That is thought to have happened in an accident in Scotland (Dundee?) some years ago.
DME substitution was included in the first draft of the AMC. The reason it was removed even for the safe cases was (and this is written explicitly) to not “discourage” the installation of DMEs. Obviously I disagree with that.
so there is risk of selecting the wrong navaid from the database. That is thought to have happened in an accident in Scotland (Dundee?) some years ago.
One has to assume the pilot has read the plate. There are loads of approaches where you have say a VOR somewhere and it involves a DME distance but the DME is not the one belonging to the VOR. Or the other way round. I can’t give you examples but have seen plenty where the DME distance is not the obvious DME.
Many years ago I flew with a pilot who wanted to rent my TB20, so we went for a flight and the first thing he did was fly the Shoreham NDB/DME approach with the DME displaying the Seaford (SFD) DME He didn’t realise it until really late. A famous UK IR holder of many years. He decided to chuck in his IR at that point.
So I don’t buy this at all. It is just committee power politics, and nobody sitting there will go public with who wanted what. You just hear it verbally years later… “Germans wanted this, French wanted that” etc.
the theoretical accuracy of an NDB (and certainly a VOR) is in some cases better than the theoretical accuracy of LNAV
That is BS in all of real life so it is like saying “in theory, bees cannot fly”. Or “this is fine in practice but it will never work in theory” which is a famous cartoon from a certain country.
to not “discourage” the installation of DMEs.
Given that level of idiocy, anything is believable.
Politics is the art of the possible, but why pretend that something is what it is not?
I know it is hard to believe, but the theoretical accuracy of an NDB (and certainly a VOR) is in some cases better than the theoretical accuracy of LNAV
LNAV with WAAS GPS is angular guidance is clearly way better than NDB even when talking about concepts, you can fly 1/2 dot CDI angular deviation, clearly the “theoretical accuracy” of WAAS GPS is far superior than NDB, anyone who think differently seems to live in a different planet
The protected area of LNAV is based on lateral 0.3nm (to support legacy LNAV or TSO129), I am sure you can come up with obstacles on short final where LNAV minima is higher than NDB minima (you can also theorise that LPV & LVNAV DH can be higher and worse than lateral LNAV MDH due to obstacles geometry, in practice this is rarely a concern)
The only reason we need to carry an ADF when you have GPS-W is institutional inertia rather than flying risks: things have evolved since but not for the dinosaurs (“who had their time”)
Airborne_Again wrote:
Let me first say that I don’t agree with the AMC – I do find it too restrictive. But I don’t agree that it’s worthless. E.g. NDBs/VORs used as fixes in an instrument approach procedure can now be substituted by RNAV fixes.
@Airborne_Again, as it is acceptable means of compliance, what stops you from producing your own and using those?
It is NCO, so what is the problem?
