T-6A INSTRUMENT NAVIGATION
Airborne and ground checkpoints consist of certified radials that should be received at specific
points on the airport surface or over specific landmarks while airborne in the immediate vicinity
of the airport.
Should an error in excess of + 4° be indicated through use of a ground check, or + 6° using the
airborne check, IFR flight shall not be attempted without first correcting the source of the error.
Locations of airborne checkpoints are published in AP1, and ground checkpoints are published in
the local airfield information and posted via signage at the actual point. These points are usually
located in the runway hold short area.
TACTICAL AIR NAVIGATION
For reasons peculiar to military or naval operations (unusual sitting conditions, the pitching and
rolling of a naval vessel, etc.) the civil VOR/DME system of air navigation was considered
unsuitable for military or naval use. Therefore, a new navigational system, Tactical Air
Navigation (TACAN), was developed by the military and naval forces to address their unique
Although the T-6A has no TACAN azimuth capability, a functional
knowledge is required to understand VORTAC and DME usage.
TACAN ground equipment consists of either a fixed or mobile transmitting unit. The airborne
unit in conjunction with the ground unit reduces the transmitted signal to a visual presentation of
both azimuth and distance information. A TACAN operates in the Ultra High Frequency (UHF)
band of frequencies. The system has a total of 252 channels available and is identified by two
sets of channel numbers from 1 to 126, with suffixes "X" or "Y" for discrimination between the
Several forms of TACAN malfunctions can give false or erroneous information to the navigation
1. Due to the nature of the TACAN signal, it is possible for the TACAN azimuth to lock-on in
multiples of 40º from the true bearing with no warning flag appearing. Aircrew should cross-
check against other available NAVAIDS to verify TACAN azimuth. Re-channeling the airborne
receiver to deliberately cause unlock may correct the problem. Although some TACAN sets are
designed to eliminate 40º lock-on errors, the aircrews should still cross-check the bearing.
2. This occurs when the aircraft is in a position to receive TACAN signals from more than
one ground station on the same channel, normally at high altitudes. DME, azimuth, or
identification from either ground station may be received.
3. False or incorrect lock-on is caused by misalignment or excessive wear of the airborne
equipment channel selection mechanism. Re-channeling from the selected channel number and
1-4 INTRODUCTION TO NAVIGATION SYSTEMS