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Suppose you have a Cessna 208 Grand Caravan Amphibian and you want to use VORTAC stations on military bases (or somewhere else). Is it possible? Is it legal?

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    $\begingroup$ It's legal. Tuning a VOR signal is different to area based restrictions. If the wanted the signal restricted, they would encrypt it like some GPS signals. $\endgroup$ – Rodney Hawkins Dec 25 '17 at 19:26
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    $\begingroup$ @RodneyHawkins I don’t think it is possible to encrypt a VOR signal, which is what you are tuning to when tracking a VORTAC. If they wanted to restrict civilian use they would put in a TACAN and leave off the VOR. $\endgroup$ – JScarry Dec 25 '17 at 19:58
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Totally legal to tune it up & use it. If it is a VORTAC, it will work just like every other VORTAC out there. If it is a TACAN, you may be able to get DME from it, but you won”t get bearing from it without a TACAN receiver.

Many, perhaps most VOR’s out there are in fact VORTAC’s — the TACAN station is colocated with the VOR. It is possible to have a VOR-DME station, which gives a civillian user everything a VORTAC does, but no bearing info to TACAN-only military aircraft. And you can have a VOR station with no associated DME at all.

But you won’t find any rule prohibiting you from tuning up any of the above - doesn’t exist (at least in the U.S., nor anywhere else I’ve ever heard of). If the military wanted a NAVAID they could use that you couldn’t, they could put up a TACAN using a channel that civillian DME receivers can’t pair with (ex ch 16X “pairs” to 135.9 - not a frequency in the range civil VOR receivers can tune to) and not publish it. But realistically, they’d probably just use a GPS coordinate & call it good.

(Edit: as @UnrecognizedFallingObject mentioned, it is not the “Y” TACAN channels that conventional VOR receivers can’t pair with, but there are some channels you can’t get DME from using normal VOR tuning — see this chart.)

Flying over that navaid on a military base may entail issues with the airspace involved, but that is its own issue, unrelated to using or not using the navaid.

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    $\begingroup$ BTW: it seems that most DME receivers can use Y-channels (you'll see plenty of civil DMEs published as "Chan 54(Y)" or whatever, see the I-SAJ DME used with the ILS for KORD RWY 09L for ex.) $\endgroup$ – UnrecognizedFallingObject Dec 25 '17 at 23:03
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    $\begingroup$ @UnrecognizedFallingObject - Good catch! Looks like the X channels pair up to frequencies like 112.30, while the Y channels pair up with .05 higher, so 112.35. Edited post above to reflect that. $\endgroup$ – Ralph J Dec 25 '17 at 23:21
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Absolutely. A VORTAC is nothing more than a VOR colocated with a TACAN. Most VOR-DMEs in the US are VORTACs. If there happens to be one located on a base you are certainly still able to use it.

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Short answer: A VORTAC station combines a VOR-DME and a TACAN. It is the result of a cooperation between civil and military worlds to share the same DME (and the navaid place).

  • Civil aircraft use includes accessing the VOR part (civil), the DME part (civil and military), but not the TACAN bearing transponder, said otherwise they access the VOR-DME equivalent, or for what civilians are concerned, a VORTAC is a VOR-DME.

  • They are not equipped for receiving the TACAN bearing equipment, though nothing prevent them to be equipped with the related UHF receiver.


More details: A VORTAC station is composed of three signal generators:

  • A VOR (VHF) signal used for civil bearing determination.
  • A DME (UHF) signal used for range determination
  • An UHF signal used for military bearing determination, in theory 9 times more accurate than a VOR.

DME and UHF bearing station components are interrogated by the aircraft, contrary to the VOR which broadcasts continuously.

When civilians use a VORTAC, they actually use the two first signals (VOR-DME). Military use the two last signals (TACAN) and the VOR as a backup if they are equipped, which is normally the case.

Pure TACAN have only the UHF bearing determination signal and the DME signal.

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Source

Their little size, compared to a VOR-DME, allow them to be used on ships. More: Wikipedia article on TACAN, and How does Tactical Air Navigation work?

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