Aeronautical Information Manual (AIM), page 80

Index   79 -- Page 80 -- 81

placing the receiver in the non-sequencing mode.
When the receiver is in the non-sequencing mode,
bearing and distance are provided to the selected
waypoint and the receiver will not sequence to the
next waypoint in the route until placed back in the
auto sequence mode or the pilot selects a different
waypoint. The pilot may have to compute the ATD
to stepdown fixes and other points on overlay
approaches, due to the receiver showing ATD to the
next waypoint rather than DME to the VOR or ILS
ground station.
(k) Impact of Magnetic Variation on PBN

(1) Differences may exist between PBN
systems and the charted magnetic courses on
ground-based NAVAID instrument flight procedures
(IFP), enroute charts, approach charts, and Standard
Instrument Departure/Standard Terminal Arrival

(SID/STAR) charts. These differences are due to the
magnetic variance used to calculate the magnetic
course. Every leg of an instrument procedure is first
computed along a desired ground track with reference
to true north. A magnetic variation correction is then
applied to the true course in order to calculate a
magnetic course for publication. The type of
procedure will determine what magnetic variation
value is added to the true course. A ground-based
NAVAID IFP applies the facility magnetic variation

of record to the true course to get the charted magnetic

course. Magnetic courses on PBN procedures are

calculated two different ways. SID/STAR procedures

use the airport magnetic variation of record, while
IFR enroute charts use magnetic reference bearing.
PBN systems make a correction to true north by
adding a magnetic variation calculated with an
algorithm based on aircraft position, or by adding the
magnetic variation coded in their navigational
database. This may result in the PBN system and the
procedure designer using a different magnetic
variation, which causes the magnetic course
displayed by the PBN system and the magnetic course
charted on the IFP plate to be different. It is important
to understand, however, that PBN systems, (with the
exception of VOR/DME RNAV equipment) navigate
by reference to true north and display magnetic
course only for pilot reference. As such, a properly
functioning PBN system, containing a current and
accurate navigational database, should fly the
correct ground track for any loaded instrument
procedure, despite differences in displayed magnetic

course that may be attributed to magnetic variation
application. Should significant differences between
the approach chart and the PBN system avionics'
application of the navigation database arise, the
published approach chart, supplemented by NOT-
AMs, holds precedence.
(2) The course into a waypoint may not
always be 180 degrees different from the course
leaving the previous waypoint, due to the PBN
system avionics' computation of geodesic paths,
distance between waypoints, and differences in
magnetic variation application. Variations in
distances may also occur since PBN system
distance-to-waypoint values are ATDs computed to
the next waypoint and the DME values published on
underlying procedures are slant-range distances
measured to the station. This difference increases
with aircraft altitude and proximity to the NAVAID.

(l) GPS Familiarization

Pilots should practice GPS approaches in visual
meteorological conditions (VMC) until thoroughly
proficient with all aspects of their equipment
(receiver and installation) prior to attempting flight
in instrument meteorological conditions (IMC).
Pilots should be proficient in the following areas:
(1) Using the receiver autonomous integ-
rity monitoring (RAIM) prediction function;

(2) Inserting a DP into the flight plan,

including setting terminal CDI sensitivity, if required,

and the conditions under which terminal RAIM is

available for departure;

(3) Programming the destination airport;
(4) Programming and flying the ap-
proaches (especially procedure turns and arcs);
(5) Changing to another approach after
selecting an approach;

(6) Programming and flying "direct"
missed approaches;
(7) Programming and flying "routed"
missed approaches;
(8) Entering, flying, and exiting holding
patterns, particularly on approaches with a second
waypoint in the holding pattern;

(9) Programming and flying a "route" from
a holding pattern;
(10) Programming and flying an approach
with radar vectors to the intermediate segment;

1-1-26 Navigation Aids

Page 80 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   79 -- Page 80 -- 81