INSTRUMENT FLIGHT RULES WORKBOOK
between like frequencies is inadequate. DME, azimuth, or identification from either
ground station may be received. This is not a malfunction of either air or ground
equipment, but a result of interfering signals of two ground facilities.
False or incorrect lock-on. False or incorrect lock-on indications in the aircraft can be
caused by misalignment or excessive wear of the airborne crystal selector assembly.
Selection of a numbered TACAN channel activates a drum and wiper arrangement
which rotates until the wiper contacts the proper crystal on the drum. These crystal
contact points are very small and close together. Wear or misalignment can cause the
wiper to miss the proper crystal and contact the wrong one. This can result in no
station being tuned in or the wrong station. When this occurs, rechanneling of the
receiver may result in the correct channel being selected.
5. Precautionary actions. The following precautionary actions should be taken to guard
against in-flight use or erroneous navigational signals:
ALWAYS check the identification of any NAVAID station and monitor it during
ALWAYS use all suitable navigational equipment aboard the aircraft and cross-check
heading and bearing information.
NEVER overfly preplanned estimated time of arrivals without careful cross-check of
NAVAIDs and ground checkpoints.
CHECK notices to airmen (NOTAMs) and FLIP before flight for possible
malfunctions or limitations on NAVAIDs to be used.
DISCONTINUE USE of any suspected NAVAID and confirm aircraft position with
radar or other equipment.
1-22 INTRODUCTION TO AIRBORNE NAVIGATION AND COMMUNICATIONS
EQUIPMENT AND PRINCIPLES OF OPERATION