Twin Wasp

Yes, the VOR is one system, the DME another. Different operating freqs, the DME/TACAN freq is linked to the VOR freq so you only dial one. If it is just a TACAN you can track down the ghost freq (VHF) to dial in to get the DME distance but you won't have azmuth.

EvilGN

What "book" did you quote the answer from FLYR?

KC10 FATboy

Crazy. You'll never see me fly one of these approaches unless I have an FMS/GPS backup. Once you lose that radial, all bets are off that you're going to get it back. Just because the FAA says you can do it, doesn't mean it is safe to do so.

USMCFLYR

This was from a Chapter in the TI 8200.52 - Flight Inspection Handbook.
It is bascially the 'How To' book of flight inspection.

KC - Now we aren't talking about the VOR all of the sudden failing - that could happen at any time. This question was specifically addressing that a DME arcing approach could still be inspected and found within tolerance if the arc transversed an area of unusable radials as long as certain radials (described above) where found to be within all tolerances.

In your case of the VOR failing while in that area of restricted use and then missing the inbound radial and you continue to arc around and hit an obstacle, I'm sure there is a TERPs answer to the protection afforded.

Edit: Ok - just had a TERPster walk by and posed the question too.
His answer - first the VOR receiver would flag 'off' and you would know that the VOR is now out of service. I asked him to answer only the obstacle clearnance question and he said "no". The approach is only built to have the protection provided within the tolerances of the DME arc which is part of the approach. If you were arcing another 90 degs around you could run into something (in theory).

Also to be sure we understand what we are talking here - I'm talking about flight inspecting an approach and what constitutes within tolerance. I'm not saying that the FAA is saying fly this approach in hard IMC. Before reading this passage, if I had seen a VOR/DME arcing approach to an airfield, but on the approach plates (or in the AF/D) there was a note that there were unusable radials contained within that DME arc then I would have thought there was a mistake.

USMCFLYR

brianb

I don't know about you guys, but, if im in actual IMC conditions flying a DME arc utilizing a VOR/DME as my course guidance in mountainous terrain and I lost any portion of said VOR/DME, its time to "punch out"!

USMCFLYR

One of the great things about this job is that a vast majority of the inspections must be carried out in VMC conditions! I have a second cup of coffee at the FBO while I watch some of the others launch out into some nasty weather!

USMCFLYR