TACAN is a military UHF navigation aid operating around 1000 MHz.  The ranging function of both TACAN and DME beacons is identical in operation, based on the transponder principle; however, TACAN also provides bearing information to military users in the form of a continuous transmission.  Military aircraft fitted with a TACAN receiver will receive range and bearing information from a TACAN station.  Civil aircraft with a DME receiver can receive the range information but will not see the bearing information as the signal is in the UHF band.  However, a civil aircraft will only ‘see’ a TACAN if the NAVAID is coded into the aircraft’s navigation database.

For a TACAN to be coded into an civil aircraft’s database, the beacon must conform to the standards for DME set out in Annex 10 and the NAVAID must be listed in the State’s AIP.

In Attachment H, Volume I, Annex 10 entitled ‘Strategy for Rationalisation of conventional radio navigation aids and the evolution toward supporting performance-based navigation’ the following statement is made by ICAO for DME considerations:

ANSPs should take maximum advantage of cross-border and military facilities (TACAN), provided the necessary agreements can be put in place

Therefore, when considering GNSS reversion, the ANSP should consider military ranging sources if the terrestrial infrastructure is not robust.

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