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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 waypoints
are used when the aircraft must fly over the
point prior to starting a turn.
NOTEFIG
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.
AIM 2/14/08
1-2-2 Area Navigation (RNAV) and Required Navigation Performance (RNP)
(a) 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: “via 087 track to CHEZZ WP.” See
FIG 1-2-2.
(b) 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: “left
turn direct BARGN WP.” See FIG 1-2-3.
FIG 1-2-2
Track to Fix Leg Type
FIG 1-2-3
Direct to Fix Leg Type
2/14/08 AIM
Area Navigation (RNAV) and Required Navigation Performance (RNP) 1-2-3
(c) Course to Fix. A Course to Fix (CF) leg
is a path that terminates at a fix with a specified course
at that fix. Narrative: “via 078 course to PRIMY
WP.” See FIG 1-2-4.
FIG 1-2-4
Course to Fix Leg Type
(d) Radius to Fix. A Radius to Fix (RF) leg
is defined as a constant radius circular path around a
defined turn center that terminates at a fix. See
FIG 1-2-5.
FIG 1-2-5
Radius to Fix Leg Type
(e) Heading. A Heading leg may be defined
as, but not limited to, a Heading to Altitude (VA),
Heading to DME range (VD), and Heading to Manual
Termination, i.e., Vector (VM). Narrative: “climb
runway heading to 1500”, “heading 265, at 9 DME
west of PXR VORTAC, right turn heading 360”, “fly
heading 090, expect radar vectors to DRYHT INT.”
3. Navigation Issues. Pilots should be aware
of their navigation system inputs, alerts, and
annunciations in order to make better-informed
decisions. In addition, the availability and suitability
of particular sensors/systems should be considered.
(a) GPS. Operators using TSO-C129 systems
should ensure departure and arrival airports are
entered to ensure proper RAIM availability and CDI
sensitivity.
(b) DME/DME. Operators should be aware
that DME/DME position updating is dependent on
FMS logic and DME facility proximity, availability,
geometry, and signal masking.
(c) VOR/DME. Unique VOR characteristics
may result in less accurate values from
VOR/DME position updating than from GPS or
DME/DME position updating.
(d) Inertial Navigation. Inertial reference
units and inertial navigation systems are often
coupled with other types of navigation inputs,
e.g.,DME/DME or GPS, to improve overall
navigation system performance.
NOTESpecific
inertial position updating requirements may
apply.
4. Flight Management System (FMS). An
FMS is an integrated suite of sensors, receivers, and
computers, coupled with a navigation database.
These systems generally provide performance and
RNAV guidance to displays and automatic flight
control systems.
Inputs can be accepted from multiple sources such as
GPS, DME, VOR, LOC and IRU. These inputs may
be applied to a navigation solution one at a time or in
combination. Some FMSs provide for the detection
　
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