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NAVAID SERVICE VOLUME
Each class of VHF NAVAID (VOR/DME/TACAN)
has an established operational service volume to
ensure adequate signal coverage and frequency protection
from other NAVAIDs on the same frequency.
The maximum distance at which NAVAIDs are usable
varies with altitude and the class of the facility. When
using VORs for direct route navigation, the following
guidelines apply:
- For operations above FL 450, use aids not more
than 200 NM apart. These are High Altitude (H)
class facilities and are depicted on en route high
altitude charts.
- For operations that are off established airways
from 18,000 feet MSL to FL 450, use aids not
more than 260 NM apart. These are High Altitude
(H) class facilities and are depicted on en route
high altitude charts.
- For operations that are off established airways
below 18,000 feet MSL, use aids not more than
80 NM apart. These are Low Altitude (L) class
facilities and are shown on en route low altitude
charts.
- For operations that are off established airways
between 14,500 feet MSL and 17,999 feet MSL
in the conterminous United States, use H-class
facilities not more than 200 NM apart.
The use of satellite based navigation systems has
increased pilot requests for direct routes that take the
aircraft outside ground based NAVAID service volume
limits. These direct route requests are approved only in
a radar environment, and approval is based on pilot
responsibility for staying on the authorized direct route.
ATC uses radar flight following for the purpose of aircraft
separation. On the other hand, if ATC initiates a
direct route that exceeds NAVAID service volume limits,
ATC also provides radar navigational assistance as
necessary. More information on direct route navigation
is located in the En Route RNAV Procedures section
later in this chapter.
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