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Navigation Aids

improvement is sufficient to enable approach
procedures with GPS/WAAS glide paths (vertical


The FAA has completed installation of 3

GEO satellite links, 38 WRSs, 3 WMSs, 6 GES, and
the required terrestrial communications to support
the WAAS network including 2 operational control
centers. Prior to the commissioning of the WAAS for
public use, the FAA conducted a series of test and
validation activities. Future dual frequency opera-
tions are planned.


GNSS navigation, including GPS and

WAAS, is referenced to the WGS

84 coordinate

system. It should only be used where the Aeronautical
Information Publications (including electronic data
and aeronautical charts) conform to WGS

84 or

equivalent. Other countries’ civil aviation authorities
may impose additional limitations on the use of their
SBAS systems.

b. Instrument Approach Capabilities


A class of approach procedures which

provide vertical guidance, but which do not meet the
ICAO Annex 10 requirements for precision ap-
proaches has been developed to support satellite
navigation use for aviation applications worldwide.
These procedures are not precision and are referred to
as Approach with Vertical Guidance (APV), are
defined in ICAO Annex 6, and include approaches
such as the LNAV/VNAV and localizer performance
with vertical guidance (LPV). These approaches
provide vertical guidance, but do not meet the more
stringent standards of a precision approach. Properly
certified WAAS receivers will be able to fly to LPV
minima and LNAV/VNAV minima, using a WAAS
electronic glide path, which eliminates the errors that
can be introduced by using Barometric altimetry.


LPV minima takes advantage of the high

accuracy guidance and increased integrity provided
by WAAS. This WAAS generated angular guidance
allows the use of the same TERPS approach criteria
used for ILS approaches. LPV minima may have a
decision altitude as low as 200 feet height above
touchdown with visibility minimums as low as 




mile, when the terrain and airport infrastructure
support the lowest minima. LPV minima is published
on the RNAV (GPS) approach charts (see Paragraph


5, Instrument Approach Procedure Charts).


A different WAAS-based line of minima,

called Localizer Performance (LP) is being added in
locations where the terrain or obstructions do not
allow publication of vertically guided LPV minima.
LP takes advantage of the angular lateral guidance
and smaller position errors provided by WAAS to
provide a lateral only procedure similar to an ILS
Localizer. LP procedures may provide lower minima
than a LNAV procedure due to the narrower obstacle
clearance surface.


WAAS receivers certified prior to TSO

C145b and


C146b, even if they have LPV capability, do not

contain LP capability unless the receiver has been
upgraded. Receivers capable of flying LP procedures must
contain a statement in the Aircraft Flight Manual (AFM),
AFM Supplement, or Approved Supplemental Flight
Manual stating that the receiver has LP capability, as well
as the capability for the other WAAS and GPS approach
procedure types.


WAAS provides a level of service that

supports all phases of flight, including RNAV (GPS)
approaches to LNAV, LP, LNAV/VNAV, and LPV
lines of minima, within system coverage. Some
locations close to the edge of the coverage may have
a lower availability of vertical guidance.

c. General Requirements


WAAS avionics must be certified in

accordance with Technical Standard Order (TSO)

C145(), Airborne Navigation Sensors Using

the (GPS) Augmented by the Wide Area Augmenta-
tion System (WAAS); or TSO

C146(), Stand


Airborne Navigation Equipment Using the Global
Positioning System (GPS) Augmented by the Wide
Area Augmentation System (WAAS), and installed in
accordance with AC 20

138, Airworthiness Ap-

proval of Positioning and Navigation Systems.


GPS/WAAS operation must be conducted in

accordance with the FAA

approved aircraft flight

manual (AFM) and flight manual supplements. Flight
manual supplements will state the level of approach
procedure that the receiver supports. IFR approved
WAAS receivers support all GPS only operations as
long as lateral capability at the appropriate level is
functional. WAAS monitors both GPS and WAAS
satellites and provides integrity.


GPS/WAAS equipment is inherently capable

of supporting oceanic and remote operations if the
operator obtains a fault detection and exclusion
(FDE) prediction program.