AIM

4/3/14

1−2−1

Area Navigation (RNAV) and Required Navigation Performance (RNP)

Section 2. Area Navigation (RNAV) and Required

Navigation Performance (RNP)

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1. Area Navigation (RNAV)

a. General.

RNAV is a method of navigation that

permits aircraft operation on any desired flight path

within the coverage of ground or space based

navigation aids or within the limits of the capability

of self−contained aids, or a combination of these. In

the future, there will be an increased dependence on

the use of RNAV in lieu of routes defined by

ground−based navigation aids.

RNAV routes and terminal procedures, including

departure procedures (DPs) and standard terminal

arrivals (STARs), are designed with RNAV systems

in mind. There are several potential advantages of

RNAV routes and procedures:

1.

Time and fuel savings,

2.

Reduced dependence on radar vectoring,

altitude, and speed assignments allowing a reduction

in required ATC radio transmissions, and

3.

More efficient use of airspace.

In addition to information found in this manual,

guidance for domestic RNAV DPs, STARs, and

routes may also be found in Advisory Circu-

lar 90−100A, U.S. Terminal and En Route Area

Navigation (RNAV) Operations.

b. RNAV Operations.

RNAV procedures, such

as DPs and STARs, demand strict pilot awareness and

maintenance of the procedure centerline. Pilots

should possess a working knowledge of their aircraft

navigation system to ensure RNAV procedures are

flown in an appropriate manner. In addition, pilots

should have an understanding of the various

waypoint and leg types used in RNAV procedures;

these are discussed in more detail below.

1. Waypoints.

A waypoint is a predetermined

geographical position that is defined in terms of

latitude/longitude coordinates. Waypoints may be a

simple named point in space or associated with

existing navaids, intersections, or fixes. A waypoint

is most often used to indicate a change in direction,

speed, or altitude along the desired path. RNAV

procedures make use of both fly−over and fly−by

waypoints.

(a) Fly

−by waypoints. Fly−by waypoints

are used when an aircraft should begin a turn to the

next course prior to reaching the waypoint separating

the two route segments. This is known as turn

anticipation.

(b) Fly

−over waypoints. Fly−over way-

points are used when the aircraft must fly over the

point prior to starting a turn.

NOTE

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FIG 1

−2−1 illustrates several differences between a fly−by

and a fly

−over waypoint.

FIG 1

−2−1

Fly

−by and Fly−over Waypoints

2. RNAV Leg Types.

A leg type describes the

desired path proceeding, following, or between

waypoints on an RNAV procedure. Leg types are

identified by a two−letter code that describes the path

(e.g., heading, course, track, etc.) and the termination

point (e.g., the path terminates at an altitude, distance,

fix, etc.). Leg types used for procedure design are

included in the aircraft navigation database, but not

normally provided on the procedure chart. The

narrative depiction of the RNAV chart describes how

a procedure is flown. The “path and terminator

concept” defines that every leg of a procedure has a

termination point and some kind of path into that

termination point. Some of the available leg types are

described below.