ILS Question

[germb747]

I had someone ask me today whether or not it's legal to fly the ILS or LOC/DME RWY 15 approach into KSKF with the KSY Tacan out of service.

http://204.108.4.16/d-tpp/1009/00371ILD15.PDF

I told him "Yes" because the procedure says "RADAR OR DME REQUIRED" and Tacan isn't listed as part of the title of the approach.

The next question was "Since FEGSA isn't a "/RADAR" fix, how would you identify it without DME?" Besides the fact that you'd be talking to tower (not radar) at FEGSA, how would you verify you were in fact at 2400' at the FAF (in other words, the correct glideslope) as called for in the procedure?

 

[nosehair]

the procedure says "RADAR OR DME REQUIRED" and Tacan isn't listed as part of the title of the approach.

if it's a vortac, the dme information is missing. Is radar available?

 

[z987k]

You don't have to be talking to tower at the FAF. If the tacan was out you should stay with approach until the FAF then call tower, or they should tell you to then call tower. It also says Radar OR DME like you said. Approach would call the FAF for you. Also the one tower I've been in, tower had a scope up top as well. I don't know if they could call the fix for you but they had radar. Don't know if this is how it works at all class C/B.

RADAR REQUIRED- A term displayed on charts and approach plates and included in FDC NOTAMs to alert pilots that segments of either an instrument approach procedure or a route are not navigable because of either the absence or unusability of a NAVAID. The pilot can expect to be provided radar navigational guidance while transiting segments labeled with this term.

 

[Lefty]

if it's a vortac, the dme information is missing. Is radar available?

It is not a VORTAC, it is a TACAN.

 

[z987k]

It is not a VORTAC, it is a TACAN.

But it has DME information on 112.0. So, if the tacan is out, there would be no DME.

 

[Autothrust Blue]

It is not a VORTAC, it is a TACAN.

I would say that you'd need radar identification of FEGSA intersection if the KSY DME (the DME part of the TACAN - without knowing precisely how TACAN works other than knowing that TACANs do provide civil DME as well) is out of service.

I assume FEGSA is depicted on the radar scopes of whichever approach control is responsible (non-DME equipped aircraft REQUIRE radar assistance on this approach), as you'll be pointed towards the approach gate while being vectored and the approach gate starts at the FAF.

 

[Ollie]

I told him "Yes" because the procedure says "RADAR OR DME REQUIRED" and Tacan isn't listed as part of the title of the approach.

The next question was "Since FEGSA isn't a "/RADAR" fix, how would you identify it without DME?" Besides the fact that you'd be talking to tower (not radar) at FEGSA, how would you verify you were in fact at 2400' at the FAF (in other words, the correct glideslope) as called for in the procedure?

This might be a stupid question, but how do you propose to execute the published missed approach procedure with the KSY TACAN OTS? What about with no commo?

It seems like there might be some confusion between the FAF for this approach as a non-precision vs. a precision procedure. If you're executing this as a non-precision procedure then you could, in theory, get ATC to RADAR fix it for you if KSY is OTS then use the appropriate minima. In that case you're not using the glideslope for guidance.

 

[Lefty]

But it has DME information on 112.0. So, if the tacan is out, there would be no DME.

TACAN is very similar to a VOR/DME system, more often than not VOR/DME facilities are located with TACAN. This facility is only a TACAN however. The TACAN utilizes a rotating antenna system so if the antenna fails (ie - stops rotating) only the DME would be operable. This TACAN appears to be located with a civil use type DME that utilizes a VHF frequency. If the TACAN completely fails, you should still have DME info.


So basically what you said but exactly the opposite

Two answers to the proposed question. TACAN is OTS we can assume that both azimuth and DME is inop. The DME information for this SPECIFIC example (Lackland AFB) is on a seperate VHF freq. You would still have DME info.

 

[z987k]

TACAN is very similar to a VOR/DME system, more often than not VOR/DME facilities are located with TACAN. This facility is only a TACAN however. The TACAN utilizes a rotating antenna system so if the antenna fails (ie - stops rotating) only the DME would be operable. This TACAN appears to be located with a civil use type DME that utilizes a VHF frequency. If the TACAN completely fails, you should still have DME info.

I don't know exactly how a tacan works, so please correct me if I'm wrong. Also if you have a link or can explain exactly how it works that would be great.

The rotating part gives the azimuth just like the rotating part is the VOR in civilian. At the field I trained at we had a vortac. If the rotating part of the tacan failed, it would say tacan azimuth ots. If the whole thing(tacan) failed, it would say tacan ots and there would be no dme, but the VOR would still work as the VOR and azimuth are two different systems whereas the DME is integrated into the tacan. That is the tacan transponder performs the function of dme. They are not separate units. It is just broadcast on different frequencies for civilian purposes.

 

[Ollie]

If you're executing this as a non-precision procedure then you could, in theory, get ATC to RADAR fix it for you if KSY is OTS then use the appropriate minima. In that case you're not using the glideslope for guidance.

Whoops, disregard this. I just scanned briefly over this chart and didn't notice that the non-precision approach was a LOC/DME approach. If you were to execute the non-precision approach depicted here, you would require DME. As Lefty mentioned though, just because the TACAN is OTS doesn't mean that the DME is necessarily OTS...

 

[Lefty]

Whoops, disregard this. I just scanned briefly over this chart and didn't notice that the non-precision approach was a LOC/DME approach. If you were to execute the non-precision approach depicted here, you would require DME. As Lefty mentioned though, just because the TACAN is OTS doesn't mean that the DME is necessarily OTS...

What Ollie said ^^^

The reference for this would be in the AIM, 5-4-5, a3(c).

 

[Lefty]

I don't know exactly how a tacan works, so please correct me if I'm wrong. Also if you have a link or can explain exactly how it works that would be great.

The rotating part gives the azimuth just like the rotating part is the VOR in civilian. At the field I trained at we had a vortac. If the rotating part of the tacan failed, it would say tacan azimuth ots. If the whole thing(tacan) failed, it would say tacan ots and there would be no dme, but the VOR would still work as the VOR and azimuth are two different systems whereas the DME is integrated into the tacan. That is the tacan transponder performs the function of dme. They are not separate units. It is just broadcast on different frequencies for civilian purposes.

I see what your saying, the only difference is Lackland does not have a VOR. This facility is a Tacan only, so:

Is the Tacan's DME info broadcasted on 112.0 or is a civil use DME co-located with this TACAN?

 

[Polar742]

Just use GPS in lieu of ground based DME.

Done. :beer:

 

[z987k]

I see what your saying, the only difference is Lackland does not have a VOR. This facility is a Tacan only, so:

Is the Tacan's DME info broadcasted on 112.0 or is a civil use DME co-located with this TACAN?

That's the thing. From my understanding, there is never a "co-located" DME since the DME equipment is the tacan, that is there is no separate physical equipment. At a VORTAC the DME is always just broadcast also on the civilian frequency, as it's the tacan doing the work. Why would a Tacan(Bascially a VOR/DME minus the civilian azimuth in this case) only be any different?

Now this last part of this part I'm guessing on, but it would make sense. DME doesn't actually operate in the VHF range the VOR's do, rather they are in the UHF. The DME frequency is paired to a corresponding VOR VHF. So say you punch in 112.0, the DME equipment on board will know that this corresponds to channel XX on the UHF for the space reserved for DME. That is the same way tacan receivers work. Notice on this approach the tacan says channel 57. I would be willing to bet VHF 112.0 is paired to channel 57 in the 960-1215Mhz range. These frequencies are the frequencies that both DME and Tacan operate on, that is they are in the same band.
Anyways, I am pretty sure there is no difference whatsoever in tacan and dme function or physical device. 2 names, 1 thing. therefore, if the tacan is out, so is the DME. If tacan azimuth is out, DME works.
I'm pulling this information from wikipedia on VOR/VORTAC/DME/TACAN and my personal experience with our tacan at the field and when parts are ots, what doesn't work.

In fact after looking at some charts, it appears all vortacs with a civilian frequency of 112.0 also operate on channel 57. This leads me to believe I am correct in this matter.

 

[Autothrust Blue]

Just use GPS in lieu of ground based DME.

Done. :beer:

But I'm /A WHAT DO YOU MEAN I HAVE NO MOVING MAP?

 

[MikeD]

That's the thing. From my understanding, there is never a "co-located" DME since the DME equipment is the tacan, that is there is no separate physical equipment. At a VORTAC the DME is always just broadcast also on the civilian frequency, as it's the tacan doing the work. Why would a Tacan(Bascially a VOR/DME minus the civilian azimuth in this case) only be any different?

In that respect, correct. TACAN is different with different restrictions in other ways though.


For this particular IAP into KSKF, use radar to ID the FAF, either for FAF purposes or to use the glideslope check altitude, and you're fine.

 

[Lefty]

I did some more research (Avweb, Airnav, AIM) and what z says is legit, so borrowing all info posted above:

-KSY Tacan contains azimuth and DME information.
1)Channel 57 contains azimuth and DME for military acft.
2)DME information is broadcasted on 112.0, paired with Localizer gives you final course guidance and range information.


For the OP:

ILS 15 - YES you can fly this approach if the TACAN is OTS, as long as approach fixes for you.


LOC/DME 15 - NO, as per the info in the AIM (5-4-5, a3(c)) you must have equipment listed in the approach title (ie. LOC/DME), if the Tacan is OTS completely then you have no DME info. If just the azimuth is OTS then you still have DME and could fly this approach. All dependent on what the notams say for the NAVAID.




Please correct if any of this is wrong.

Another interesting tidbit of information, like DME, glideslope information is paired on carrier frequencies associated 1:1 with VHF frequencies. (You can refernce paired frequencies in Table 1-1-4 in the AIM.

 

[z987k]

2)DME information is broadcasted on 112.0, paired with Localizer gives you final course guidance and range information.

This no longer matters at all to the OP, but the DME information is not broadcast on 112.0. Telling the DME equipment in your aircraft the DME is on 112.0 it then knows which frequency in the UHF the DME is actually on because the UHF frequencies are paired to the VOR VHF frequencies, DME frequencies are in the UHF not VHF, but we never deal with them since pairing them makes this transparent to the pilot.

An interesting thing that you should be able to do is, at any tacan only station you should be able to get dme off of it if you know what frequency is paired to the channel the vortac operates on.

 

[Lefty]

This no longer matters at all to the OP, but the DME information is not broadcast on 112.0. Telling the DME equipment in your aircraft the DME is on 112.0 it then knows which frequency in the UHF the DME is actually on because the UHF frequencies are paired to the VOR VHF frequencies, DME frequencies are in the UHF not VHF, but we never deal with them since pairing them makes this transparent to the pilot.

I referenced this above regarding carrier frequencies. It does matter to the OP since it would be the only way to fly it if he does not have a Tacan receiver. It is all in the wording, the DME info is broadcasted (via the associated freq) on 112.0 (since there is no way to input the associated UHF freq.)

An interesting thing that you should be able to do is, at any tacan only station you should be able to get dme off of it if you know what frequency is paired to the channel the vortac operates on.

Incorrect, you have no equipment in your aircraft that you can input a DME UHF frequency.

 

[z987k]

I referenced this above regarding carrier frequencies. It does matter to the OP since it would be the only way to fly it if he does not have a Tacan receiver. It is all in the wording, the DME info is broadcasted (via the associated freq) on 112.0 (since there is no way to input the associated UHF freq.)





Incorrect, you have no equipment in your aircraft that you can input a DME UHF frequency.

No, if you have the channel the tacan is operating on, say 57, then if you knew the paired frequency, in this case 112.0, you could put 112.0 in your dme and should be able to get dme off it. Another example would be you run across a tacan on channel 37. If you put 110.0 into your dme, you should get distance. By putting 110.0 in, the dme knows to look at the uhf frequency that corresponds to channel 37. So you can put in certain uhf frequencies, you just don't know you're doing it.

An no, no DME info is broadcast on 112.0. I don't know if I'm misreading you. The paired frequencies does not mean it is also broadcast on, rather the DME knows where to look because 57 is paired to 112.0. And of course the channels correspond to a frequency. In the ILS case of pairing, since we have a table, when you put 108.1 in, you are also putting 334.7 in. 334.7 is where the glideslope will look for information, not 108.1.

A quick google search even turned this up. To deduce the channel from tacan to it's VHF pair you add 1063 up to channel 57 and add 1053 if it is 70 or above. Nothing was mentioned in between those, but it seems to work with the tacans and vortac's I looked up on a sectional.
channel 57 + 1063 = 1120 channel 37 + 1063 = 1110
And here is a list of the pairings: http://braun-home.net/michael/info/radio_navigation/TACAN-channels.xls

Now you can go around and get DME off of all those tacans, lol.