Index   89 -- Page 90 -- 91

AIM                                                                                                          12/10/15



should possess a working knowledge of their aircraft                 (b) RNAV Leg Types. A leg type describes
navigation system to ensure RNAV procedures are              the desired path proceeding, following, or between
flown in an appropriate manner. In addition, pilots          waypoints on an RNAV procedure. Leg types are
should have an understanding of the various                  identified by a two-letter code that describes the path
waypoint and leg types used in RNAV procedures;              (e.g., heading, course, track, etc.) and the termination
these are discussed in more detail below.                    point (e.g., the path terminates at an altitude, distance,
                                                             fix, etc.). Leg types used for procedure design are
        (a) Waypoints. A waypoint is a predeter-
                                                             included in the aircraft navigation database, but not
mined geographical position that is defined in terms
                                                             normally provided on the procedure chart. The
of latitude/longitude coordinates. Waypoints may be
                                                             narrative depiction of the RNAV chart describes how
a simple named point in space or associated with
                                                             a procedure is flown. The "path and terminator
existing navaids, intersections, or fixes. A waypoint
                                                             concept" defines that every leg of a procedure has a
is most often used to indicate a change in direction,
                                                             termination point and some kind of path into that
speed, or altitude along the desired path. RNAV
                                                             termination point. Some of the available leg types are
procedures make use of both fly-over and fly-by
                                                             described below.
waypoints.
          (1) Fly-by waypoints. Fly-by waypoints                       (1) Track to Fix. A Track to Fix (TF) leg
are used when an aircraft should begin a turn to the         is intercepted and acquired as the flight track to the
next course prior to reaching the waypoint separating        following waypoint. Track to a Fix legs are
the two route segments. This is known as turn                sometimes called point-to-point legs for this reason.
anticipation.                                                Narrative: "direct ALPHA, then on course to
                                                             BRAVO WP." See FIG 1-2-3.
         (2) Fly-over waypoints. Fly-over way-
points are used when the aircraft must fly over the                    (2) Direct to Fix. A Direct to Fix (DF) leg
point prior to starting a turn.                              is a path described by an aircraft's track from an initial
                                                             area direct to the next waypoint. Narrative: "turn
NOTE-                                                        right direct BRAVO WP." See FIG 1-2-4.
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                                             FIG 1-2-3
                                                                              Track to Fix Leg Type




1-2-2                                             Performance-Based Navigation (PBN) and Area Navigation (RNAV)