BASIC INSTRUMENT PROCEDURES
Confirm that the:
DME OFF flag disappears.
TACAN needle points to 180º.
CDI bar centers.
After 15 seconds, confirm that the:
Test light is extinguished.
Both return to "pretest indications."
If the test light comes on and remains on during, and/or after the completion of the
test, a malfunction is indicated.
TACAN Calibration Checks. Ground checkpoints consist of a certified radial and DME
that should be received at a specific point on the airport surface. Taxiway signs located at hold
short areas usually designate these "checkpoints". Should an error in bearing exist in excess of
+ 4º or in DME of greater than 0.5 NM or 3% of the distance to the station, whichever is greater,
flight should not be attempted without first correcting the source of error. Errors observed which
are within the prescribed limits should be considered as applicable only to the radial and
transmitter checked, and as a check that the receiver is properly operating. Zero error should be
assumed when flying other radials and other TACAN stations, and no compensation made for
the observed error.
VORTAC. VORTAC is a combination VOR (Very-high-frequency Omnidirectional
Range) station and TACAN station, which operate simultaneously. A TACAN-
equipped aircraft receives azimuth and distance information from the TACAN
station, while the VOR/DME-equipped aircraft receives azimuth information from the
VOR station (Figure 1-2) and distance information from the TACAN station. The
two ground installations are usually housed in a single building and the coincident
position of the antennas establishes a common navigational fix for two navigation
systems. VORTAC is not an integration of the VOR and TACAN systems but rather
a coexistence of the two systems, which enables aircraft equipped with different types
of navigation receivers to navigate on the same airways.
BASIC INSTRUMENT PROCEDURES 1-13