Tactical Air Navigation

CHAPTER ONE

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

requirements.

NOTE

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

sets.

Several forms of TACAN malfunctions can give false or erroneous information to the navigation

display equipment:

1. Due to the nature of the TACAN signal, it is possible for the TACAN azimuth to lock-on in

multiples of 40 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 40 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