VOR, VORTAC, and TACAN NAVAIDs are classified according to their operational use:
terminal (T), low altitude (L), or high altitude (H). The use of the facilities beyond the
prescribed limitations may result in unreliable indications in the aircraft. You should refer
to Flight Services, FAAO 7110.10, and the AIM for specific altitude and distance
limitations and associated clearance limitations.
VOR Receiver Checks
The FAA VOR test facility (VOT) transmits a test signal that provides users a convenient
means to determine the operational status and accuracy of a VOR receiver while on the
ground where a VOT is located. Airborne use is permitted. Its use is strictly limited to
those areas and altitudes specifically authorized in the Airport/Facility Directory or
Besides the VOT, naval air stations have checkpoints on a taxiway or ramp area
marked to indicate the distance and bearing to the TACAN/VOR.
Instrument Landing System
The most precise enroute navigation system is of little value unless an approach and
landing can be successfully completed at the aircraft's destination. Since the early days
of instrument flight, approach procedures have been developed and used with a high
degree of safety. The Instrument Landing System (ILS) provides an approach path for
exact alignment and descent of an aircraft on final approach to a runway.
The ILS ground equipment has two highly directional transmitting systems and, along
the approach, three (or fewer) marker beacons. The directional transmitters are known
as the localizer and the glide slope transmitter. The system may be divided functionally
into three parts, as shown in Table 2-7.
Localizer and glide slope
Marker beacon and DME
Approach, touchdown, centerline, and runway lights
Table 2-7 -- ILS ground equipment