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AIM

10/12/17

5−1−14

Preflight

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

enroute 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 enroute

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 enroute 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. These direct route requests

will be approved only in a radar environment, with

approval based on pilot responsibility for navigation

on the authorized direct route. Radar flight following

will be provided by ATC for ATC purposes.

5. At times, ATC will initiate a direct route in a

radar environment which exceeds NAVAID service

volume limits. In such cases ATC will provide radar

monitoring and navigational assistance as necessary.

6. Airway or jet route numbers, appropriate to

the stratum in which operation will be conducted,

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. The MEAs and other altitudes

shown on low altitude IFR enroute charts pertain to

those route segments within controlled airspace, and

those altitudes may not meet obstruction clearance

criteria when operating off those routes.

d. Area Navigation (RNAV)

1. Random impromptu routes can only be

approved in a radar environment. Factors that will be

considered by ATC in approving random impromptu

routes include the capability to provide radar

monitoring and compatibility with traffic volume and

flow. ATC will radar monitor each flight, however,

navigation on the random impromptu route is the

responsibility of the pilot.

2. Pilots of aircraft equipped with approved area

navigation equipment may file for RNAV routes

throughout the National Airspace System and may be

filed for in accordance with the following procedures.

(a) File airport-to-airport flight plans.
(b) File the appropriate RNAV capability

certification suffix in the flight plan.

(c) Plan the random route portion of the flight

plan to begin and end over appropriate arrival and

departure transition fixes or appropriate navigation

aids for the altitude stratum within which the flight

will be conducted. The use of normal preferred

departure and arrival routes (DP/STAR), where

established, is recommended.

(d) File route structure transitions to and from

the random route portion of the flight.

(e) Define the random route by waypoints.

File route description waypoints by using degree-

distance fixes based on navigational aids which are

appropriate for the altitude stratum.

(f) File a minimum of one route description

waypoint for each ARTCC through whose area the

random route will be flown. These waypoints must be

located within 200 NM of the preceding center’s

boundary.

(g) File an additional route description

waypoint for each turnpoint in the route.