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Navigation Aids

receivers use menus where the pilot selects the
airport, the runway, the specific approach procedure
and finally the IAF, there is also a channel number
selection method. The pilot enters a unique 5


number provided on the approach chart, and the
receiver recalls the matching final approach segment
from the aircraft database. A list of information
including the available IAFs is displayed and the pilot
selects the appropriate IAF. The pilot should confirm
that the correct final approach segment was loaded by
cross checking the Approach ID, which is also
provided on the approach chart.


The Along

−Track Distance (ATD) during the

final approach segment of an LNAV procedure (with
a minimum descent altitude) will be to the MAWP. On
LNAV/VNAV and LPV approaches to a decision
altitude, there is no missed approach waypoint so the

−track distance is displayed to a point normally

located at the runway threshold. In most cases, the
MAWP for the LNAV approach is located on the
runway threshold at the centerline, so these distances
will be the same. This distance will always vary
slightly from any ILS DME that may be present, since
the ILS DME is located further down the runway.
Initiation of the missed approach on the LNAV/
VNAV and LPV approaches is still based on reaching
the decision altitude without any of the items listed in
14 CFR Section 91.175 being visible, and must not be
delayed while waiting for the ATD to reach zero. The
WAAS receiver, unlike a GPS receiver, will
automatically sequence past the MAWP if the missed
approach procedure has been designed for RNAV.
The pilot may also select missed approach prior to the
MAWP; however, navigation will continue to the
MAWP prior to waypoint sequencing taking place.


−1−19. Ground Based Augmentation

System (GBAS) Landing System (GLS)

a. General


The GLS provides precision navigation

guidance for exact alignment and descent of aircraft
on approach to a runway. GBAS equipment provides
localized differential augmentation to the Global
Positioning System (GPS).


To remain consistent with international terminology, the
FAA will use the term GBAS in place of the former term
Local Area Augmentation System (LAAS).


GLS displays three

−dimension vertical and

horizontal navigation guidance to the pilot much like

ILS. GLS navigation is based on GPS signals
augmented by position correction, integrity parame-
ters, and approach path definition information
transmitted over VHF from the local GBAS ground
station. One GBAS station can support multiple GLS
precision approaches to nearby runways within the
GBAS’s maximum use distance.


GLS provides guidance similar to ILS

approaches for the final approach segment, though
the approach service volume has different dimen-
sions (see FIG 1

−1−8). The GLS approach is

constructed using the RNP approach (RNP APCH)
navigation specification, and may include vertically

guided turn(s) after the IAF or on the missed approach
procedure. Portions of the approach prior to an IAF
and after the final approach segment may also require
Area Navigation (RNAV) typically using the
Required Navigation Performance 1 (RNP 1)
navigation specification. See paragraph 1

−2−1 for

more information on navigation specifications.




consists of a GBAS Ground Facility

(GGF), at least four ground


reference stations, a

corrections processor, a VHF Data Broadcast (VDB)
uplink antenna, an aircraft GBAS receiver, and a
charted instrument approach procedure.

b. Procedure


Pilots will select the five digit GBAS channel

number of the associated GLS approach within the
Flight Management System (FMS) menu or
manually select the five digits (system dependent).
Selection of the GBAS channel number also tunes the


Following procedure selection, confirmation

that the correct GLS procedure is loaded can be
accomplished by cross checking the charted
Reference Path Indicator (RPI) or approach ID with
the cockpit displayed RPI or audio identification of
the RPI with Morse Code (for some systems).
Distance to the runway threshold will be displayed to
the pilot once the aircraft is inside the approach
service volume.


The pilot will fly the GLS approach using

many of the same techniques as ILS


including using

a heading or lateral steering mode to intercept the
GLS final approach course and then switching to the
appropriate approach navigation mode once the
aircraft is within the approach service volume and
prior to the glide path intercept point.  See also the
Instrument Procedures Handbook for more informa-
tion on GLS.


7110.65R CHG 2