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AIM 

6/17/21 

VOR, NDB, ILS) final approach fixes on GPS 
overlay approaches. These CNFs provide the GPS 
with points on the procedure that allow the overlay 
approach to mirror the ground-based sensor 
approach. These points should only be used by the 
GPS system for navigation and should not be used by 
pilots for any other purpose on the approach. The 
CNF concept has not been adopted or recognized by 
the International Civil Aviation Organization 
(ICAO). 

(3) 

GPS approaches use fly

over and 

fly

by waypoints to join route segments on an 

approach. Fly

by waypoints connect the two 

segments by allowing the aircraft to turn prior to the 
current waypoint in order to roll out on course to the 
next waypoint. This is known as turn anticipation and 
is compensated for in the airspace and terrain 
clearances. The MAWP and the missed approach 
holding waypoint (MAHWP) are normally the only 
two waypoints on the approach that are not fly

by 

waypoints. Fly

over waypoints are used when the 

aircraft must overfly the waypoint prior to starting a 
turn to the new course. The symbol for a fly-over 
waypoint is a circled waypoint. Some waypoints may 
have dual use; for example, as a fly

by waypoint 

when used as an IF for a NoPT route and as a fly-over 
waypoint when the same waypoint is also used as an 
IAF/IF hold-in-lieu of PT. When this occurs, the less 
restrictive (fly-by) symbology will be charted. 
Overlay approach charts and some early stand

alone 

GPS approach charts may not reflect this convention. 

(4) 

Unnamed waypoints for each airport 

will be uniquely identified in the database. Although 
the identifier may be used at different airports (for 
example, RW36 will be the identifier at each airport 
with a runway 36), the actual point, at each airport, is 
defined by a specific latitude/longitude coordinate. 

(5) 

The runway threshold waypoint, nor-

mally the MAWP, may have a five

letter identifier 

(for example, SNEEZ) or be coded as RW## (for 
example, RW36, RW36L). MAWPs located at the 
runway threshold are being changed to the RW## 
identifier, while MAWPs not located at the threshold 
will have a five

letter identifier. This may cause the 

approach chart to differ from the aircraft database 
until all changes are complete. The runway threshold 
waypoint is also used as the center of the Minimum 
Safe Altitude (MSA) on most GPS approaches. 

(j)  Position Orientation. 

Pilots should pay particular attention to position 
orientation while using GPS. Distance and track 
i n f o r m a t i on a r e provided to the next active 
waypoint, not to a fixed navigation aid. Receivers 
may sequence when the pilot is not flying along an 
active route, such as when being vectored or 
deviating for weather, due to the proximity to another 
waypoint in the route. This can be prevented by 
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 

Systems 

(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 

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