Temporary loss of VOR/LOC signal on approach

dutch_flyer wrote:

Incidentally it didn’t occur today and I passed.

Congrats! NCYankee wrote:

Never heard of it being used. Not in the PCG or AIM. I have heard of terms such as service volume. Closest is in the AIM Fig 1-1-6, Limits of Localizer Coverage. Otherwise, in my 53 years as a US pilot, I have never come across this acronym.

Same here, never heard of DOC during my IFR training or flying. I was about to look it up when someone posted the explanation. Could it be that it’s used in the UK only?

172driver wrote:

Same here, never heard of DOC during my IFR training or flying. I was about to look it up when someone posted the explanation. Could it be that it’s used in the UK only?

I have seen it several times so it is not UK only. It may well be an ICAO concept which is not used by the FAA.

Definitely not limited to the UK.

dutch_flyer wrote:

It was then that he said he’d made a mistake and we were tracking the VOR instead of the RNP course. The 530 automatically puts the LOC in standby when you call up an ILS, then switches to VLOC when you begin your intercept. Problem is the active was set to the VOR when this happened

That is one reason that I avoid doing an ILS here in the US where I have a choice of an RNAV (GPS) with LPV verses an ILS. ILS is way more complicated. I posted the difference in the setup for an ILS vs an LPV, there are many more opportunities to screw up with an ILS. Here is what I posted in another forum where the question was asked, “Why not just fly the ILS?”

I have a GTN 750 with a G500TXi. and Stec 60-2.

For an ILS, I do the following:

Load the approach
Activate VTF
Clear Lawyer message
Make the Localizer frequency the active Nav frequency.
Confirm the ident and proper display on frequency window on GTN 750.
When on vectors, on the G500TXi, switch to VLOC (this is not automatic, although the GTN 750 will auto switch to VLOC)
Confirm the green needles and Localizer annunciation with the ident on the GTN 750.
Confirm the CRS is correctly set.
When on the missed approach, activate Missed approach procedure on GTN 750.

For an LPV, I do the following:

Load the approach
Activate VTF
Verify LPV is annunciated
When on the missed approach, activate Missed approach procedure on GTN

As a side note, with the GNS430W has more to do as you have to switch back to GPS before doing the missed approach and you have to ident the Localizer frequency by listening to the dot-dash audio. The GNS530W will at least decode the audio and display the localizer ident code.

dutch_flyer wrote:

Speaking of tests and equipment challenges, the examiner did something a bit “creative” that turned into a bit of an exciting approach. He had mentioned I would fly the VOR approach for the 2D requirement, but in the air decided to have me request the RNP but dial in the ILS on the 530W and fly it on GPS instead (so I’d have lateral guidance only). I was in actual IMC, with 1000 BKN or so, and was getting vectors. It seemed like something I would never do in practice but felt preferable to doing the VOR, so I just went along (no other real options right?).

Then as I was getting vectors and intercepting the final approach course, he started playing a bit with the 530, and I really didn’t know what he was doing. I decided just to keep flying the airplane and ignore whatever it was, until my needle suddenly jumped to the right. It was then that he said he’d made a mistake and we were tracking the VOR instead of the RNP course. The 530 automatically puts the LOC in standby when you call up an ILS, then switches to VLOC when you begin your intercept. Problem is the active was set to the VOR when this happened. Anyway, it all worked in the end but was a good reminder to double check everything is set up correctly!

I think automatic switch GPS/VLOC happens right before FAF/FAP but it’s a user option that needs to be ticked in AUX/SETUP menu (same as “North up”), the automatic switch is gradual to avoid AP disconnect, a manual switch is not smooth, if ILS was loaded in GPS then ILS frequency will be active but if you reload VOR in GPS you get VOR frequency in NAV1(GPS) but you could have VOR frequency in NAV2 with another switch to drive CDI, you also have Freq1/Freq2 flip-flop in NAV1 !!

There are two ways to end up with VOR driving CDI,
- You were sending CDI = NAV1 with ILS loaded in NAV1 and VOR = NAV2, then examiner reloaded VOR approach in GPS by mistake or flipped Freq1/Freq2 in NAV1, CDI = NAV1 = VOR
- You were sending CDI = NAV1 with ILS loaded in NAV1 and VOR = NAV2, then examiner switched CDI = NAV2 by mistake, CDI = NAV2 = VOR

Reloading or reactivate any approach in GPS will flip the switch VLOC back to GPS as long as I keep CDI = NAV2 for en-route & emergencies and I do everything in GPS/NAV1 without inputting any frequency by hand, it’s easy to handle, except the day when ILS/VOR frequencies changes and GPS databases has not been updated yet…

NCYankee wrote:

ILS is way more complicated.

NCYankee wrote:

I have a GTN 750 with a G500TXi.

I have the same setup and while I agree in principle (with the additions bra has made), what is really happening here, is a dramatic reduction in redundancy we apply when flying LPV:
NCYankee wrote:

Load the approach
Activate VTF
Verify LPV is annunciated
When on the missed approach, activate Missed approach procedure on GTN

So, compared to what you have described for ILS, you do not check the WAAS-channel used (equivalent to checking the ILS frequency that the GTN attuned), you do not double check if you loaded the right approach (e.g. by checking if CRS is set correctly) and you also do not check if the TXI-Needle is actually showing the deflection from GPS.

If we would set the same redundancy requirements when flying LPV, the only two true differences on a GTN/TXI setup is confirming the “lawyer message” (i.e. that GPS overlay is for information purposes only) and pressing VLOC on the TXI. Not really so much more effort…

Malibuflyer wrote:

So, compared to what you have described for ILS, you do not check the WAAS-channel used (equivalent to checking the ILS frequency that the GTN attuned), you do not double check if you loaded the right approach (e.g. by checking if CRS is set correctly) and you also do not check if the TXI-Needle is actually showing the deflection from GPS.

No I don’t check the WAAS channel used as I see it as an alternative method of selecting the approach and not needed when loading an approach using the approach dialog, On the approach selection, the airport ID, approach name and transition are displayed along with the Channel ID. To utilize the Channel ID, one would view the chart to read the channel ID and enter the Channel ID instead of the airport, approach, transition dialog. That is way more work and more error prone. I can validate I am selecting the proper approach much easier using the airport, approach name and transition. The LPV indication and the CDI showing VTF and the correct FAF is more useful to me. Unlike the ILS where the OBS course is a changeable parameter, the GPS procedure uses point to point and the course is an auto selection by the system and is not changeable by the pilot. Also, unlike the ILS, the GPS procedure does not have to have a frequency tuned to standby and then set into the active navigation frequency and the ident determined. Also, with the GPS, which is used for enroute navigation, there is no need to switch the CDI needle from Magenta needles on any portion of the procedure, either the final approach course or the missed approach course.

In giving IPC or as a safety pilot, I have seen dozens of more errors in the setup for an ILS than an LPV, I even made a few myself.

Malibuflyer wrote:

you do not check the WAAS-channel used

Are you really supposed to do that? In contrast to the ILS frequency, the SBAS “channel” is only an identifier.

Do you guys read the FAS data blocks in AIP text & DB code as well ?