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4. In addition to providing the correction signal,
the WAAS GEO provides an additional pseudorange
measurement to the aircraft receiver, improving the
availability of GPS by providing, in effect, an
additional GPS satellite in view. The integrity of GPS
is improved through real-time monitoring, and the
accuracy is improved by providing differential
corrections to reduce errors. The performance
improvement is sufficient to enable approach
procedures with GPS/WAAS glide paths (vertical
guidance).
5. The FAA has completed installation of
25 WRSs, 2 WMSs, 4 GUSs, and the required
terrestrial communications to support the WAAS
network. Prior to the commissioning of the WAAS for
public use, the FAA has been conducting a series of
test and validation activities. Enhancements to the
initial phase of WAAS will include additional master
and reference stations, communication satellites, and
transmission frequencies as needed.
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 new class of approach procedures which
provide vertical guidance, but which do not meet the
ICAO Annex 10 requirements for precision approaches has been developed to support satellite
navigation use for aviation applications worldwide.
These new procedures called Approach with Vertical
Guidance (APV), are defined in ICAO Annex 6, and
include approaches such as the LNAV/VNAV
procedures presently being flown with barometric
vertical navigation (Baro-VNAV). 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 these
LNAV/VNAV procedures using a WAAS electronic
glide path, which eliminates the errors that can be
introduced by using Barometric altimetery.
2. A new type of APV approach procedure, in
addition to LNAV/VNAV, is being implemented to
take 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. The resulting approach procedure
minima, titled LPV (localizer performance with
vertical guidance), may have a decision altitude as
low as 200 feet height above touchdown with
visibility minimums as low as 1
/2 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). |
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