Limitations - P-12820088

T-45C TS INav 03; ADV INav-01

Use and Operation of TACAN, VOR, VOR/DME

5. Limitations

a. Line of sight

b. Standard Service Volume (SSV)

NOTE: SSV defines the reception limits of unrestricted

NAVAIDs which are usable for random/unpublished route

navigation.

The reason why federal airways are limited to a maximum

Fig 3: VOR

altitude of FL 450 is due to the service volume of VORs. The

Frequency Overlap

service volume is predicated on the limited number of available

VOR frequencies for airway navigation (total of 59). Present

FCC and FAA standards permit as many as 20 VORs to use

the same frequency. The problem with this is that the usable

range of VOR decreases with altitude due to overlapping

signals from VORs using the same frequency.

From 18,000 ft AGL up to and including 45,000 ft AGL at radial

distances out to 130 nm

NOTE: Standard Service Volume limitations do not apply to

published IFR routes or procedures.

6. Identified by 3-letter aural Morse code identifier or recorded automatic

voice alternating with Morse code identifier

7. Most can be used to transmit voice communications to aircraft as

well as scheduled and/or urgent weather information. An example

is Hazardous In-flight Weather Advisory Service/HIWAS, a

program for broadcasting hazardous weather information

Fig 4: Cones of Confusion

(Significant Meteorological Information, Center Weather Advisories,

Airman’s Meteorological Information, Severe Weather Forecast

Alerts, and urgent Pilot Weather Reports) on a continuous basis

over selected VORs

8. There is a negligible “cone of confusion” over a VOR antenna. Due

to its size, station passage over a VOR is a recognized fix. Therefore,

“over the station holding” can be conducted directly over a VOR

station

Page 3-7

(2-02) Original