AIM

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Navigation Aids

GPS−only operation and satisfies the requirements

for basic GPS equipment.

7.

Unlike TSO−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.

(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

nonprecision 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 individu-
ally evaluated, removal of the 

NA

 from RNAV

(GPS) and GPS procedures will take some time.

NOTE

−

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 capabilit-

ies. 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−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 smaller integrity limits) are approved to fly the

LPV line of minima. The lateral integrity changes

dramatically from the 0.3 NM (556 meter) limit for

GPS, LNAV and LNAV/VNAV approach mode, to 40

meters for LPV. It also provides vertical integrity

monitoring, which bounds the vertical error to 50

meters for LNAV/VNAV and LPVs with minima of

250’ or above, and bounds the vertical error to 35

meters for LPVs with minima below 250’.

2.

When an approach procedure is selected and

active, the receiver will notify the pilot of the most

accurate level of service supported by the combina-

tion of the WAAS signal, the receiver, and the

selected approach, using the naming conventions on

the minima lines of the selected approach procedure.

For example, if an approach is published with LPV

minima and the receiver is only certified for

LNAV/VNAV, the equipment would indicate

“LNAV/VNAV available,” even though the WAAS

signal would support LPV. If flying an existing

LNAV/VNAV procedure with no LPV minima, the

receiver will notify the pilot “LNAV/VNAV

available,” even if the receiver is certified for LPV

and the signal supports LPV. If the signal does not

support vertical guidance on procedures with LPV

and/or LNAV/VNAV minima, the receiver annunci-

ation will read “LNAV available.” On lateral only

procedures with LP and LNAV minima the receiver

will indicate “LP available” or “LNAV available”

based on the level of lateral service available. Once

the level of service notification has been given, the

receiver will operate in this mode for the duration of

the approach procedure, unless that level of service

becomes unavailable. The receiver cannot change

back to a more accurate level of service until the next

time an approach is activated.

NOTE

−

Receivers do not “fail down” to lower levels of service
once the approach has been activated. If only the