background image




Navigation Aids

improvement is sufficient to enable approach

procedures with GPS/WAAS glide paths (vertical


5. 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.

6. 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

1. 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.

2. 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

5−4−5, Instrument Approach Procedure Charts).

3. 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

TSO−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.

4. 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

1. WAAS avionics must be certified in

accordance with Technical Standard Order (TSO)

TSO−C145(), Airborne Navigation Sensors Using

the (GPS) Augmented by the Wide Area Augmenta-

tion System (WAAS); or TSO−C146(), Stand−Alone

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.

2. 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.

3. GPS/WAAS equipment is inherently capable

of supporting oceanic and remote operations if the

operator obtains a fault detection and exclusion

(FDE) prediction program.