In the above illustration (Figure 9), although your position over the ground is 8nm from the
TACAN station, your RMI and DME indicator will indicate 10 DME, your slant range from
At most distances from the TACAN station this range difference is negligible; however,
when the aircraft is directly overhead the TACAN station, the slant range will equal the
aircraft's altitude in nautical miles.
7. TACAN can be used to provide distance between two aircraft.
The air-to-air mode of the TACAN can provide distance from one aircraft to another. In
the A/A mode, the TACAN transmits and receives slant range distance in nautical miles to
another aircraft. No magnetic bearing information is generated in the A/A mode. When using
the A/A mode each aircraft must tune. its TACAN channel 63 channels apart from the other
aircraft. A good gouge number to use is 29/92.
A VORTAC is, quite simply, the physical presence of both a TACAN and a VOR station in
the same location. When a TACAN equipped aircraft tunes in the channel of the VORTAC
station, it is actually tuning to the TACAN portion of the facility. When a VOR equipped
aircraft tunes the 4-digit VHF frequency, it is utilizing the VOR portion. Neither navaid (VOR
or TACAN) affects the display of the other physically co-located navaid.
RADIO AIDS TO NAVIGATION