AIM 

3/21/24 

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

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over and fly

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by waypoints to join route segments on an approach. Fly

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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 missed approach waypoint (MAWP) will always be a fly

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over waypoint. A holding 

waypoint will always be designed as a fly

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over waypoint in the navigational database but may be charted as a 

fly

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by event unless the holding waypoint is used for another purpose in the procedure and both events require 

the waypoint to be a fly

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over event. Some waypoints may have dual use; for example, as a fly

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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

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in

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lieu of PT. Since the waypoint can only be charted one way, when this situation occurs, the fly

−

by 

waypoint symbol will be charted in all uses of the waypoint. 

(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, normally the MAWP, may have a five

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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. 

(i)  Position Orientation. 

Pilots should pay particular attention to position orientation while using 

GPS. Distance and track information are 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. 

(j)  Impact of Magnetic Variation on PBN Systems 

(1) 

Differences may exist between PBN systems and the charted magnetic courses on ground

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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 

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Navigation Aids