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AIM

10/12/17

1−2−2

Performance−Based Navigation (PBN) and Area Navigation (RNAV)

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.

(a) Waypoints. A waypoint is a predeter-

mined 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.

(1) 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.

(2) Fly−over waypoints. Fly−over way-

points are used when the aircraft must fly over the

point prior to starting a turn.

NOTE−

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

and a fly−over waypoint.

FIG 1−2−2

Fly−by and Fly−over Waypoints

(b) 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.

(1) Track to Fix. A Track to Fix (TF) leg

is intercepted and acquired as the flight track to the

following waypoint. Track to a Fix legs are

sometimes called point−to−point legs for this reason.

Narrative: “direct ALPHA, then on course to

BRAVO WP.” See FIG 1−2−3.

(2) Direct to Fix. A Direct to Fix (DF) leg

is a path described by an aircraft’s track from an initial

area direct to the next waypoint. Narrative: “turn

right direct BRAVO WP.” See FIG 1−2−4.

FIG 1−2−3

Track to Fix Leg Type