Garmin 255A User Manual

GNC 255A/255B

Pilot’s Guide

© 2012 Garmin Ltd. or its subsidiaries. All rights reserved.

This manual reflects the operation of System Software version 2.00, or later. Some differences in operation
may be observed when comparing the information in this manual to later software versions.

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Tel: [phone] Fax: [phone]

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Tel : [phone] Fax : ( 65 ) 63480278

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November 2012 Printed in the U.S.A.

LIMITED WARRANTY

All Garmin avionics products are warranted to be free from defects in materials or workmanship for:
two years from the date of purchase for new Remote-Mount and Panel-Mount products; one year
from the date of purchase for new portable products and any purchased newly-overhauled products;
six months for newly-overhauled products exchanged through a Garmin Authorized Service Center;
and 90 days for factory repaired or newly-overhauled products exchanged at Garmin in lieu of repair.
Within the applicable period, Garmin will, at its sole option, repair or replace any components that
fail in normal use. Such repairs or replacement will be made at no charge to the customer for parts
or labor, provided that the customer shall be responsible for any transportation cost. This warranty
does not apply to: (i) cosmetic damage, such as scratches, nicks and dents; (ii) consumable parts,
such as batteries, unless product damage has occurred due to a defect in materials or workmanship;
(iii) damage caused by accident, abuse, misuse, water, flood, fire, or other acts of nature or external
causes; (iv) damage caused by service performed by anyone who is not an authorized service
provider of Garmin; or (v) damage to a product that has been modified or altered without the written
permission of Garmin. In addition, Garmin reserves the right to refuse warranty claims against
products or services that are obtained and/or used in contravention of the laws of any country.

THE WARRANTIES AND REMEDIES CONTAINED HEREIN ARE EXCLUSIVE AND IN LIEU OF ALL OTHER
WARRANTIES, WHETHER EXPRESS, IMPLIED OR STATUTORY, INCLUDING ANY LIABILITY ARISING
UNDER ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE,
STATUTORY OR OTHERWISE. THIS WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS, WHICH MAY
VARY FROM STATE TO STATE.

IN NO EVENT SHALL GARMIN BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR CONSEQUENTIAL
DAMAGES, WHETHER RESULTING FROM THE USE, MISUSE OR INABILITY TO USE THE PRODUCT OR
FROM DEFECTS IN THE PRODUCT. SOME STATES DO NOT ALLOW THE EXCLUSION OF INCIDENTAL OR
CONSEQUENTIAL DAMAGES, SO THE ABOVE LIMITATIONS MAY NOT APPLY TO YOU.

Garmin retains the exclusive right to repair or replace (with a new or newly-overhauled replacement
product) the product or software or offer a full refund of the purchase price at its sole discretion.
SUCH REMEDY SHALL BE YOUR SOLE AND EXCLUSIVE REMEDY FOR ANY BREACH OF WARRANTY.

Online Auction Purchases: Products purchased through online auctions are not eligible for
warranty coverage. Online auction confirmations are not accepted for warranty verification. To obtain
warranty service, an original or copy of the sales receipt from the original retailer is required. Garmin
will not replace missing components from any package purchased through an online auction.

International Purchases: A separate warranty may be provided by international distributors for
devices purchased outside the United States depending on the country. If applicable, this warranty is
provided by the local in-country distributor and this distributor provides local service for your device.
Distributor warranties are only valid in the area of intended distribution. Devices purchased in the
United States or Canada must be returned to the Garmin service center in the United Kingdom, the
United States, Canada, or Taiwan for service.

To obtain warranty service, contact your local Garmin Authorized Service Center. For assistance in
locating a Service Center near you, visit the Garmin web site at http://www.garmin.com or contact
Garmin Customer Service at 866-739-5687.

Garmin GNC 255A/255B Pilot’s Guide

i190-01182-01 Rev. A

WARNING: For safety reasons, GNC 255 operational procedures must be
learned on the ground.

CAUTION: The Garmin GNC 255 does not contain any user-serviceable
parts. Repairs should only be made by an authorized Garmin service center.
Unauthorized repairs or modifications could void both the warranty and
the pilot’s authority to operate this device under FAA/FCC regulations.

CAUTION: The GNC 255 display uses a lens coated with a special anti­reflective coating that is very sensitive to skin oils, waxes, and abrasive
cleaners. CLEANERS CONTAINING AMMONIA WILL HARM THE ANTI­REFLECTIVE COATING. It is very important to clean the lens using a clean,
lint-free cloth and an eyeglass lens cleaner that is specified as safe for
anti-reflective coatings.

NOTE: Garmin recommends that if flying in a region with 8.33 kHz COM
channel spacing, the radio should remain in 8.33 kHz mode. This will prevent
the loss of stored user and recent frequencies.

NOTE: Do not use outdated database information. Databases used in the
system must be updated regularly in order to ensure that the information
remains current. Pilots using an outdated database do so entirely at their
own risk.

NOTE: All visual depictions contained within this document, including
screen images of the GNC 255 bezel and displays, are subject to change
and may not reflect the most current GNC 255 software. Depictions of
equipment may differ slightly from the actual equipment.

NOTE: This device complies with part 15 of the FCC Rules. Operation is
subject to the following two conditions: (1) this device may not cause
harmful interference, and (2) this device must accept any interference
received, including interference that may cause undesired operation.

NOTE: This product, its packaging, and its components contain chemicals
known to the State of California to cause cancer, birth defects, or
reproductive harm. This notice is being provided in accordance with
California’s Proposition 65. If you have any questions or would like
additional information, please refer to our web site at www.garmin.com/
prop65.

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Garmin GNC 255A/255B Pilot’s Guide

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NOTE: Canadian installations: In accordance with Canadian Radio
Specifications Standard 102 (RSS 102), RF field strength exposure to
persons from an antenna connected to this device should be limited to 60
V/m for controlled environment and 28 V/m for uncontrolled environment.

Garmin GNC 255A/255B Pilot’s Guide

iii190-01182-01 Rev. A

NOTE: This device complies with Part 15 of

the FCC limits for Class B digital devices. This

equipment generates, uses, and can radiate
radio frequency energy and, if not installed

Help us better support you by completing our

and used in accordance with the instructions,

may cause harmful interference to radio

communications. Furthermore, there is no

guarantee that interference will not occur in a

or stolen unit tracking. Please, have the serial

particular installation.

web site (www.garmin.com) and look for our

If this equipment does cause harmful

interference, the user is encouraged to try

to correct the interference by relocating the
equipment or connecting the equipment to a
different circuit than the affected equipment.

Consult an authorized dealer or other qualified

avionics technician for additional help if these

remedies do not correct the problem.

anti-reflective coating which is very sensitive to
skin oils, waxes and abrasive cleaners. It is very

important to clean the lens using an eyeglass

lens cleaner which is specified as safe for anti-

reflective coatings and a clean, lint-free cloth.

Operation of this device is subject to the
following conditions: (1) This device may

not cause harmful interference, and (2) this
device must accept any interference received,

including interference that may cause undesired

operation.

To obtain accessories for your unit, please

contact your Garmin dealer.

on-line registration form today! Registration

ensures that you will be notified of product

updates and new products and provides lost

number of your unit handy, connect to our

Product Registration link on the Home page.

The display surface is coated with a special

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Garmin GNC 255A/255B Pilot’s Guide

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Product Registration and Support

Help us better support you by completing your online registration today!

Have the serial number of your product handy and connect to the Garmin
web site (www.garmin.com or https://fly.garmin.com/fly-garmin). Look for the
Product Registration link on the Home page. Also, be sure to record your serial
number in the space provided.

If you have any questions, the Garmin Product Support department may be

reached Monday through Friday, 7:00 AM to 7:00 PM Central Time.

US: 913-397-8200

US Toll Free: 1-866-739-5687

Canada Toll Free: 1-866-429-9296

Garmin GNC 255A/255B Pilot’s Guide

v190-01182-01 Rev. A

Record of Revisions

Part Number Revision Date Description

190-01182-01 A 11/19/12 Initial release

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Contents

Product Registration and Support ......................................................................v

1 Getting Started ....................................................................................1-1

1.1 Product Description .............................................................................. 1-1

1.2 Pilot Controls ....................................................................................... 1-2

1.2.1 Power/Com Volume/Squelch Knob ......................................... 1-2

1.2.2 Nav Volume/ID Knob ............................................................. 1-2

1.2.3 Tuning LARGE/SMALL Concentric (Cursor) Knobs ................... 1-3

1.2.4 FLIP/FLOP Key ....................................................................... 1-3

1.2.5 C/N (Com/Nav) Key ............................................................... 1-3

1.2.6 OBS Key ................................................................................ 1-3

1.2.7 T/F (To/From) Key ...................................................................1-3

1.2.8 CLR (Clear) Key ..................................................................... 1-3

1.2.9 ENT (Enter) Key ..................................................................... 1-3

1.2.10 FUNC (Function) Key..............................................................1-4

1.2.11 MON (Monitor) Key ............................................................... 1-4

1.3 USB Port .............................................................................................. 1-4

2 Basic Operation ....................................................................................2-1

2.1 Power On ............................................................................................2-1

2.2 Com Radio ..........................................................................................2-1

2.2.1 Selecting a Com Frequency .................................................... 2-1

2.2.2 Monitoring the Standby Com Channel ...................................2-2

2.2.3 Saving a Com Channel ..........................................................2-2

2.2.4 Com Database Look-Up ......................................................... 2-4

2.2.5 Frequency Database Reverse Look-Up .................................... 2-4

2.2.6 Emergency Channel ............................................................... 2-5

2.2.7 Stuck Mic .............................................................................. 2-5

2.2.8 Remote Frequency Selection Control ...................................... 2-5

2.3 Nav Radio ...........................................................................................2-6

2.3.1 Selecting a Nav Frequency ..................................................... 2-6

2.3.2 Saving a Nav Channel ...........................................................2-6

2.3.3 Listening to the Nav Audio Channel ....................................... 2-7

2.4 OBS Mode ........................................................................................... 2-8

2.5 Distance/Speed/Time (DST) Display ....................................................... 2-9

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3 Functions ..............................................................................................3-1

3.1 Functions Description ........................................................................... 3-1

3.2 Com Frequencies .................................................................................3-2

3.2.1 Recent Com Frequencies ........................................................ 3-2

3.2.2 Com User Frequencies ........................................................... 3-3

3.2.2.1 Viewing the Com User Frequency ........................................... 3-3

3.2.2.2 Deleting the Com User Frequency ..........................................3-3

3.2.2.3 Editing a Com User Frequency ...............................................3-4

3.2.3 Com Database Frequencies .................................................... 3-5

3.2.4 Com Nearest Airports (APT) ................................................... 3-6

3.2.5 Com Nearest Area Control Center (ACC) Frequencies .............3-7

3.2.6 Com Nearest Flight Service Station (FSS) Frequencies ............. 3-8

3.2.7 Com Nearest Weather (WX) Frequencies ................................ 3-9

3.3 Nav Frequencies ................................................................................3-10

3.3.1 Recent Nav Frequencies ....................................................... 3-10

3.3.2 Nav User Frequencies .......................................................... 3-11

3.3.2.1 Viewing the Nav User Frequency .......................................... 3-11

3.3.2.2 Deleting the Nav User Frequency .........................................3-11

3.3.2.3 Editing a Nav User Frequency ..............................................3-12

3.3.3 Nav Database Frequencies ................................................... 3-13

3.3.4 Nav Nearest VOR ................................................................. 3-14

3.4 ICS Configuration ..............................................................................3-15

3.4.1 Adjust Intercom ................................................................... 3-15

3.4.2 Aux Audio ........................................................................... 3-16

3.4.3 Intercom On/Off ..................................................................3-17

3.4.4 Speaker On/Off .................................................................... 3-17

3.5 System Configuration ......................................................................... 3-18

3.5.1 Com Spacing ....................................................................... 3-18

3.5.2 Display Brightness ...............................................................3-19

3.5.3 Display Contrast .................................................................. 3-20

3.5.4 Database Info ...................................................................... 3-20

3.5.5 Load Database ....................................................................3-21

3.5.6 Software Version .................................................................3-22

3.5.7 Serial Number .....................................................................3-22

3.6 Timers ...............................................................................................3-23

3.6.1 Setting Up the Count Down Timer ........................................ 3-23

3.6.2 Setting Up the Count Up Timer ............................................ 3-24

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3.6.3 Viewing Timers in the Com Display .......................................3-24

4 Appendix ..............................................................................................4-1

4.1 Troubleshooting ................................................................................... 4-1

4.2 Updating the Frequency Database ........................................................ 4-3

4.2.1 Downloading the Frequency Database ................................... 4-3

4.2.2 Updating the GNC 255 Frequency Database .......................... 4-3

4.3 Messages ............................................................................................ 4-4

Index .....................................................................................................Index-1

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Garmin GNC 255A/255B Pilot’s Guide

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1 GETTING STARTED

1.1 Product Description

Combining a powerful VHF communications transceiver with 200 channel

VOR, Localizer and Glideslope receivers, the GNC 255 provides a full-functioned
navigation and communications solution in a small footprint at a very affordable
price. Besides traditional Nav/Com features, the GNC 255 also incorporates
workload-reducing functions such as automatic decoding of the Morse code
station identifier for VOR/LOC, most-used frequency storage in memory, built­in course deviation indicator, and more.

The GNC 255 has the ability to monitor the standby Com frequencies. The

GNC 255’s Com radio operates in the aviation voice band, from 118.000 to

136.975 MHz, in 25 kHz steps (default). For European operations, a Com
radio configuration of 8.33 kHz steps is also available. The GNC 255 VHF Nav
receiver operates from 108 MHz to 117.95 MHz decoding both the VHF Omni
Range and Localizer navigation signals. The built-in Glideslope receiver will
automatically tune the corresponding glideslope paired frequencies (328 MHz
to 335 MHz) when the localizer is tuned. The GNC 255 is available in 10 and 16
watt com transmitter versions. The GNC 255A is available with a 10 watt com
transmitter. The GNC 255B is available with a 16 watt com transmitter.

Power On/Off,

Com Volume,

Squelch On/Off

Nav (VLOC)

Volume, Nav ID

On/Off

Frequency

Monitor Key

Com or Nav

Frequency Selection

OBS Selection

Photo Sensor

To/From Selection

Figure 1-1 GNC 255 Front Panel Description

Garmin GNC 255A/255B Pilot’s Guide

Locking

Screw

Frequency Transfer

(FLIP/FLOP) Key

Function Selection

USB Port

LARGE and
SMALL Knobs
(Frequency
Adjust)

Enter Key

Clear Data Key

1-1190-01182-01 Rev. A

1.2 Pilot Controls

The GNC 255 controls have been designed to simplify operation of the

system and minimize workload and the time required to access sophisticated
functionality. Controls are comprised of dual concentric knobs for frequency
tuning, Com volume/squelch knob, Nav volume/ID knob, and bezel keys.

1.2.1 Power/Com Volume/Squelch Knob

The Power/Com Volume/Squelch knob located in the top left

corner of the bezel controls audio volume for the Com radio.
Rotating the knob clockwise past the detent turns power on
and counter-clockwise turns power off. When the Com radio is
active, press the Power/Com Volume/Squelch knob to toggle
automatic squelch control On/Off for the Com radio.

Com Mode

Annunciator

Squelch, TX, or RX

Annunciator

Active Frequency

Annunciator

Active Nav
Frequency

Com Volume Bar Graph

Figure 1-2 Com Volume and Squelch Display Description

Standby Frequency
Annunciator

The Com radio features an automatic squelch to reject many localized noise

sources. You may override the squelch function by pressing the

Volume/Squelch

knob. This facilitates listening to a distant station or setting

Power/Com

the desired volume level.

To override the automatic squelch, press the

knob momentarily. Press the

Power/Com Volume/Squelch

Power/Com Volume/Squelch

knob again to
return to automatic squelch operation. A “SQ” indication appears to the left of
the active Com frequency window in the upper left corner of the display when
automatic squelch is overridden.

1.2.2 Nav Volume/ID Knob

The Nav Volume/ID knob located in the bottom left corner

of the bezel controls audio volume for the Nav radio. Press the
Nav Volume/ID knob and the Morse code tones will be heard.
When Morse code tone is active, “ID” will appear to the left of
the Nav active frequency.

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Garmin GNC 255A/255B Pilot’s Guide

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1.2.3 Tuning LARGE/SMALL Concentric (Cursor)

Knobs

The LARGE right and

frequencies and data entry.

LARGE, Outer Knob

SMALL right

knobs are used for tuning

SMALL, Inner Knob

1.2.4 FLIP/FLOP Key

Press and release the FLIP/FLOP key to switch between the

active (left-most) and standby (right-most) frequency. Switching
between Com frequencies is disabled while you are transmitting.

1.2.5 C/N (Com/Nav) Key

Press the C/N key to select the Com or Nav (VLOC) radio

mode.

1.2.6 OBS Key

Press the OBS key to see the current OBS setting and graphic

CDI. The OBS page will be disabled if the unit is installed with
an external converter.

1.2.7 T/F (To/From) Key

Press the T/F key to toggle between the bearing TO or radial

FROM the active VOR. The T/F page also shows Distance/Speed/
Time information. The T/F key does not operate for Localizer
frequencies.

1.2.8 CLR (Clear) Key

Pressing the CLR key erases information, cancels entries, and

resets timers.

1.2.9 ENT (Enter) Key

Press the ENT key to save selected values, to confirm a prompt,

or to save the Standby frequency.

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1.2.10 FUNC (Function) Key

The FUNC (Function) key accesses function categories for the

following: the Com Radio, Nav Radio, ICS Configuration, System
Configuration, and Timer. Pressing the FUNC key once displays
the Function mode. Pressing the FUNC key a second time exits
the Function mode.

1.2.11 MON (Monitor) Key

The MON (Monitor) key will engage the monitor function where

the Standby frequency may be monitored while still listening to
the Active frequency.

1.3 USB Port

The USB port is used to update the frequency database in the GNC 255.

NOTE: Garmin recommends the use of a USB 2.0 compatible USB flash
drive for updating the database.

1-4

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2 BASIC OPERATION

2.1 Power On

Turn the GNC 255 on by either turning the Power/Com Volume/

Squelch knob clockwise to turn the power on or, if installed,

turning on the master switch that powers the radios.

2.2 Com Radio

2.2.1 Selecting a Com Frequency

New frequencies are first selected as a Standby frequency and then toggled to
the Active side with the
display, use the LARGE and SMALL knobs on the right side of the GNC 255 to
select the desired frequency.

1. Press C/N, if necessary, to reach the Com radio function. The

2. Turn the LARGE knob to change the values in one MHz

3. Turn the SMALL knob to change the values in 25 kHz or 8.33

FLIP/FLOP

COM annunciator on the top line of the display will show.

increments. The MHz selection range is between 118 and 136
in one MHz steps.

kHz increments. The kHz selection range is between 000 and
975 kHz in 25 kHz steps or 000 and 990 kHz in 8.33 kHz steps.

key. While viewing the Standby frequency

4. Turn the LARGE and SMALL knobs clockwise to increase and

counterclockwise to decrease the frequency values. Standby
frequency selection is not inhibited during transmit.

5. When connected to a position source, nearby station identifiers

will be shown for the selected frequency. Frequencies with
multiple types will have an asterisk next to the identifier.

Asterisk Indicates Multiple Types

Exist For The Selected Frequency
Identifier and Type Shown For
The Selected Frequency

Figure 2-1 Com Frequency Selection

6. Press and release the FLIP/FLOP key to toggle the Standby
frequency to the Active frequency.

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2-1190-01182-01 Rev. A

2.2.2 Monitoring the Standby Com Channel

The Frequency Monitoring function allows you to monitor the Standby

frequency for activity, while listening to the Active frequency.

Press the MON key in the Com function to listen to the standby

frequency. A small “MN” will replace the “STB” to the left of the
Standby frequency.

Monitor

Annunciation

Figure 2-2 Com Frequency Monitor Annunciation

Standby
Frequency Being
Monitored

When the Active frequency receives a signal, the unit will switch automatically
to the Active frequency. The Active frequency quality is not affected. The
Frequency Monitor function is turned off by pressing the MON key again.
Monitoring is not canceled by switching to Nav mode.

2.2.3 Saving a Com Channel

The current Standby frequency may be saved into the Com User Frequency
database from the Com display or the Com User Function. The Com User
Frequency database can hold up to 15 frequencies.

NOTE: When switching from 8.33 kHz to 25 kHz mode, any 8.33 kHz­specific user frequencies will be deleted from the user frequency list. This
only affects the user frequencies within the 8.33 kHz spectrum.

1. Press ENT. The Standby frequency is selected and the Waypoint

name field will be active.

2. Turn the SMALL knob to select characters.

3. Turn the LARGE knob to move the cursor.

Number of
Frequencies Saved

Turn SMALL Knob
To Select Character

Press the ENT Key to Save
the Displayed Value

Figure 2-3 Com User Frequency Name Selection

Press the CLR Key To Revert
to the Previous Value

Turn LARGE Knob

To Move Cursor

4. After selecting the desired characters, press ENT.

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Garmin GNC 255A/255B Pilot’s Guide

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5. Turn the LARGE knob to select the waypoint Type.

6. Turn the SMALL knob to select the Type from the list.

Selected Wpt Type

Figure 2-4 Com User Frequency Type Selection

Frequency Type Symbol Description

TWR Tower
GND Ground
ATIS Automatic Terminal Information Service
AWS Automated Weather Observing System

ATF Aerodrome Traffic Frequency

ARR Arrival

APPR Approach

DEP Departure
CLR Clearance

CTAF Common Traffic Advisory Frequency

FSS Flight Service Station
RFS Remote Flight Service Station

MF Mandatory Frequency

UNI Unicom

Blank None

Table 2-1 - Com Frequency Type List

7. After making a selection, press ENT.

Garmin GNC 255A/255B Pilot’s Guide

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2.2.4 Com Database Look-Up

1. Press the CURSOR knob from the Com display to activate the
database look-up function.

Identifier Field Active
for Selection

Figure 2-5 Database Identifier Active for Selection

2. Turn the SMALL knob to select characters and turn the LARGE
knob to move the cursor.

Figure 2-6 Database Identifier Selection

3. After selecting the desired characters, press ENT. Turn the
SMALL knob to scroll through the list of waypoint types.

Waypoint Types with a “+” sign will have more frequencies
for the same type. After selection, the selected waypoint and
type will be remembered for 30 minutes.

Turn SMALL Knob
To Select Character

Turn LARGE Knob

To Move Cursor

Selected Identifier

Turn the SMALL Knob To
Select Frequency Type

Figure 2-7 Database Waypoint Type Selection

4. Press ENT to copy the frequency into the Standby frequency
location. Press and release the FLIP/FLOP key to swap the
Active and Standby frequencies.

2.2.5 Frequency Database Reverse Look-Up

The identifier and frequency type will be shown for Com and Nav frequencies

that are in the database when the unit is receiving a valid position input.

Waypoint Types with a “+” sign will have more frequencies for the same type.

Airport Identifier Shown

For Freqs In Database

Figure 2-8 Frequency Database Reverse Look-Up

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