AIM

4/20/23

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37

Navigation Aids

EXAMPLE

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Here is an example of a GPS testing NOTAM: 
!GPS 

06/001

 ZAB NAV GPS (INCLUDING WAAS, GBAS, AND ADS-B) MAY NOT BE AVAILABLE WITHIN A 468NM

RADIUS CENTERED AT 330702N1062540W (TCS 093044) FL400-UNL DECREASING IN AREA WITH A DECREASE
IN ALTITUDE DEFINED AS: 425NM RADIUS AT FL250, 360NM RADIUS AT 10000FT, 354NM RADIUS AT 4000FT
AGL, 327NM RADIUS AT 50FT AGL. 1406070300-1406071200.

7.

When the approach chart is annotated with the 

 symbol, site

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specific WAAS MAY NOT BE AVBL

NOTAMs or Air Traffic advisories are not provided for outages in WAAS LNAV/VNAV and LPV vertical
service. Vertical outages may occur daily at these locations due to being close to the edge of WAAS system
coverage. Use LNAV or circling minima for flight planning at these locations, whether as a destination or
alternate. For flight operations at these locations, when the WAAS avionics indicate that LNAV/VNAV or LPV
service is available, then the vertical guidance may be used to complete the approach using the displayed level
of service. Should an outage occur during the procedure, reversion to LNAV minima may be required.

NOTE

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Area

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wide WAAS NOT AVBL NOTAMs apply to all airports in the WAAS NOT AVBL area designated in the NOTAM,

including approaches at airports where an approach chart is annotated with the 

 symbol.

8.

GPS/WAAS was developed to be used within GEO coverage over North America without the need for

other radio navigation equipment appropriate to the route of flight to be flown. Outside the WAAS coverage or
in the event of a WAAS failure, GPS/WAAS equipment reverts to GPS

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only operation and satisfies the

requirements for basic GPS equipment. (See paragraph 1

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17 for these requirements).

9.

Unlike TSO

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C129 avionics, which were certified as a supplement to other means of navigation, WAAS

avionics are evaluated without reliance on other navigation systems. As such, installation of WAAS avionics
does not require the aircraft to have other equipment appropriate to the route to be flown. (See paragraph
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17 d for more information on equipment requirements.)

(a)

Pilots with WAAS receivers may flight plan to use any instrument approach procedure authorized for

use with their WAAS avionics as the planned approach at a required alternate, with the following restrictions.
When using WAAS at an alternate airport, flight planning must be based on flying the RNAV (GPS) LNAV or
circling minima line, or minima on a GPS approach procedure, or conventional approach procedure with “or
GPS” in the title. Code of Federal Regulation (CFR) Part 91 non

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precision weather requirements must be used

for planning. Upon arrival at an alternate, when the WAAS navigation system indicates that LNAV/VNAV or
LPV service is available, then vertical guidance may be used to complete the approach using the displayed level
of service. The FAA has begun removing the 

 

NA

 (Alternate Minimums Not Authorized) symbol from select

RNAV (GPS) and GPS approach procedures so they may be used by approach approved WAAS receivers at
alternate airports. Some approach procedures will still require the 

 

NA

 for other reasons, such as no weather

reporting, so it cannot be removed from all procedures. Since every procedure must be individually evaluated,
removal of the 

NA

 from RNAV (GPS) and GPS procedures will take some time.

NOTE

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Properly trained and approved, as required, TSO-C145() and TSO-C146() equipped users (WAAS users) with and using
approved baro-VNAV equipment  may plan for LNAV/VNAV DA at an alternate airport. Specifically authorized WAAS users
with and using approved baro-VNAV equipment may also plan for RNP 0.3 DA at the alternate airport as long as the pilot
has verified RNP availability through an approved prediction program.

d. Flying Procedures with WAAS

1.

WAAS receivers support all basic GPS approach functions and provide additional capabilities. One of

the major improvements is the ability to generate glide path guidance, independent of ground equipment or
barometric aiding. This eliminates several problems such as hot and cold temperature effects, incorrect altimeter
setting, or lack of a local altimeter source. It also allows approach procedures to be built without the cost of
installing ground stations at each airport or runway. Some approach certified receivers may only generate a glide
path with performance similar to Baro

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VNAV and are only approved to fly the LNAV/VNAV line of minima

on the RNAV (GPS) approach charts. Receivers with additional capability (including faster update rates and