AIM
12/2/21
and TACAN aids are assigned certain frequency
protected areas of airspace which are intended for
application to established airway and route use, and
to provide guidance for planning flights outside of
established airways or routes. These areas of airspace
are expressed in terms of cylindrical service volumes
of specified dimensions called “class limits” or
“categories.”
REFERENCE
−
AIM, Para 1
−
1
−
8, Navigational Aid (NAVAID) Service Volumes.
3.
An operational service volume has been
established for each class in which adequate signal
coverage and frequency protection can be assured. To
facilitate use of VOR, VORTAC, or TACAN aids,
consistent with their operational service volume
limits, pilot use of such aids for defining a direct route
of flight in controlled airspace should not exceed the
following:
(a)
Operations above FL 450
−
Use aids not
more than 200 NM apart. These aids are depicted on
en route high altitude charts.
(b)
Operation off established routes from
18,000 feet MSL to FL 450
−
Use aids not more than
260 NM apart. These aids are depicted on en route
high altitude charts.
(c)
Operation off established airways below
18,000 feet MSL
−
Use aids not more than 80 NM
apart. These aids are depicted on en route low altitude
charts.
(d)
Operation off established airways be-
tween 14,500 feet MSL and 17,999 feet MSL in the
conterminous U.S.
−
(H) facilities not more than 200
NM apart may be used.
4.
Increasing use of self
−
contained airborne
navigational systems which do not rely on the
VOR/VORTAC/TACAN system has resulted in pilot
requests for direct routes which exceed NAVAID
service volume limits.
5.
At times, ATC will initiate a direct route in a
surveillance environment which exceeds NAVAID
service volume limits. Pilots must adhere to the
altitude specified in the clearance.
6.
Appropriate airway or jet route numbers may
also be included to describe portions of the route to be
flown.
EXAMPLE
−
MDW V262 BDF V10 BRL STJ SLN GCK Spelled out: from
Chicago Midway Airport via Victor 262 to Bradford, Victor
10 to Burlington, Iowa, direct St. Joseph, Missouri, direct
Salina, Kansas, direct Garden City, Kansas.
NOTE
−
When route of flight is described by radio fixes, the pilot
will be expected to fly a direct course between the points
named.
7.
Pilots are reminded that they are responsible
for adhering to obstruction clearance requirements on
those segments of direct routes that are outside of
controlled airspace and ATC surveillance capability.
The MEAs and other altitudes shown on IFR en route
charts pertain to those route segments within
controlled airspace, and those altitudes may not meet
obstruction clearance criteria when operating off
those routes.
NOTE
−
Refer to 14 CFR 91.177 for pilot responsibility when flying
random point to point routes.
d. Area Navigation (RNAV)/Global Navigation
Satellite System (GNSS)
1.
When not being radar monitored, GNSS
−
equipped RNAV aircraft on random RNAV routes
must be cleared via or reported to be established on
a point
−
to
−
point route.
(a)
The points must be published NAVAIDs,
waypoints, fixes or airports recallable from the
aircraft’s navigation database. The points must be
displayed on controller video maps or depicted on the
controller chart displayed at the control position.
When applying non
−
radar separation the maximum
distance between points must not exceed 500 miles.
(b)
ATC will protect 4 miles either side of the
route centerline.
(c)
Assigned altitudes must be at or above the
highest MIA along the projected route segment being
flown, including the protected airspace of that route
segment.
2.
Pilots of aircraft equipped with approved area
navigational equipment may file for RNAV routes
throughout the National Airspace System in
accordance with the following procedures:
(a)
File airport
−
to
−
airport flight plans.
(b)
File the appropriate indication of RNAV
and/or RNP capability in the flight plan.
(c)
Plan the random route portion of the flight
plan to begin and end over appropriate arrival and
5
−
1
−
12
Preflight