5/19/22
AIM
NOTE
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To remain consistent with international terminology, the
FAA will use the term GBAS in place of the former term
Local Area Augmentation System (LAAS).
b.
An aircraft’s GLS approach capability relies on
the broadcast from a GBAS Ground Facility (GGF)
installation. The GGF installation includes at least
four ground reference stations near the airport’s
runway(s), a corrections processor, and a VHF Data
Broadcast (VDB) uplink antenna. To use the GBAS
GGF output and be eligible to conduct a GLS
approach, the aircraft requires eligibility to conduct
RNP approach (RNP APCH) operations and must
meet the additional, specific airworthiness require-
ments for installation of a GBAS receiver intended to
support GLS approach operations. When the aircraft
achieves GLS approach eligibility, the aircraft’s
onboard navigation database may then contain
published GLS instrument approach procedures.
c.
During a GLS instrument approach procedure,
the installation of an aircraft’s GLS capability
provides the pilot three
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dimensional (3D) lateral and
vertical navigation guidance much like an ILS
instrument approach. GBAS corrections augment the
GPS signal
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in
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space by offering position correc-
tions, ensures the availability of enhanced integrity
parameters, and then transmits the actual approach
path definition over the VDB uplink antenna. A
single GBAS ground station can support multiple
GLS approaches to one or more runways.
d.
Through the GBAS ground station, a GLS
approach offers a unique operational service volume
distinct from the traditional ILS approach service
volume (see FIG 1
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1
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9). However, despite the
unique service volume, in the final approach
segment, a GLS approach provides precise 3D
angular lateral and vertical guidance mimicking the
precision guidance of an ILS approach.
e.
Transitions to and segments of the published
GLS instrument approach procedures may rely on use
of RNAV 1 or RNP 1 prior to an IAF. Then, during the
approach procedure, prior to the aircraft entering the
GLS approach mode, a GLS approach procedure
design uses the RNP APCH procedure design criteria
to construct the procedural path (the criteria used to
publish procedures titled “RNAV (GPS)” in the US).
Thus, a GLS approach procedure may include paths
requiring turns after the aircraft crosses the IAF, prior
to the aircraft’s flight guidance entering the GLS
approach flight guidance mode. Likewise, the missed
approach procedure for a GLS approach procedure
relies exclusively on the same missed approach
criteria supporting an RNP APCH.
f.
When maneuvering the aircraft in compliance
with an ATC clearance to intercept a GLS approach
prior to the final approach segment (e.g. “being
vectored”), the pilot should adhere to the clearance
and ensure the aircraft intercepts the extended GLS
final approach course within the specified service
volume. Once on the GLS final approach course, the
pilot should ensure the aircraft is in the GLS approach
mode prior to reaching the procedure’s glidepath
intercept point. Once the aircraft is in the GLS flight
guidance mode and captures the GLS glidepath, the
pilot should fly the GLS final approach segment
using the same pilot techniques they use to fly an ILS
final approach or the final approach of an RNAV
(GPS) approach flown to LPV minimums. See also
the Instrument Procedures Handbook for more
information on how to conduct a GLS instrument
approach procedure.
Navigation Aids
1
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1
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37