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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−digit

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.

7. 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

along−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.

1−1−19. Ground Based Augmentation

System (GBAS) Landing System (GLS)

a. General

1. 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).

2. 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.

3. 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.

4. GLS


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

1. 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


2. 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.

3. 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