Garmin | GNC 255 | Garmin GNC 255 GNC 255A/255B Pilot's Guide

Garmin GNC 255 GNC 255A/255B Pilot's Guide
GNC 255A/255B
Pilot’s Guide
© 2012-2015 Garmin Ltd. or its subsidiaries. All rights reserved.
This manual reflects the operation of system software version 2.10 or later. Some differences in operation
may be observed when comparing the information in this manual to later software versions.
Garmin International, Inc., 1200 East 151st Street, Olathe, KS 66062, U.S.A.
Tel: 913/397.8200
Fax: 913/397.8282
Garmin AT, Inc., 2345 Turner Road SE, Salem, OR 97302, U.S.A.
Tel: 503/391.3411
Fax 503/364.2138
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SO40 9LR, U.K.
Tel. +44 (0) 870 850 1243 Fax +44 (0) 23 8052 4004
Garmin Singapore Pte. Ltd., 46 East Coast Road, #05-06 Eastgate, Singapore 428766
Tel : (65) 63480378
Fax : ( 65 ) 63480278
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April 2015
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.
190-01182-01 Rev. C
Garmin GNC 255A/255B Pilot’s Guide
i
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 uses a display coated with a special anti-reflective
coating that is very sensitive to skin oils, waxes, and abrasive cleaners.
CLEANERS CONTAINING AMMONIA WILL HARM THE ANTI-REFLECTIVE
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
190-01182-01 Rev. C
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.
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
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
particular installation.
To obtain accessories for your unit, please
contact your Garmin dealer.
The display surface is coated with a special
anti-reflective material which is very sensitive
to skin oils, waxes and abrasive cleaners. It is
very important to clean the display using an
eyeglass lens cleaner which is specified as safe
for anti-reflective coatings and a clean, lint-free
cloth.
If this equipment causes harmful interference,
the user is encouraged to try to correct the
interference by relocating the equipment or
connecting the equipment to a different circuit
other than the affected equipment. Consult an
authorized dealer or other qualified avionics
technician for additional help if these remedies
do not correct the problem.
Operation of this device is subject to the
following conditions: (1) This device may
not cause harmful interference. (2) This
device must accept any interference received,
including interference that may cause undesired
operation.
190-01182-01 Rev. C
Garmin GNC 255A/255B Pilot’s Guide
iii
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
website (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 CT.
US: 913-397-8200
US Toll Free: 1-866-739-5687
Canada Toll Free: 1-866-429-9296
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Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
Record of Revisions
Part Number Revision Date
Description
190-01182-01
A
11/19/12 Initial release
B
3/30/15 Added v2.10 functionality
C
4/7/15 Corrected Part Number on back cover
190-01182-01 Rev. C
Garmin GNC 255A/255B Pilot’s Guide
v
Contents
Product Registration and Support......................................................................iv
1
1.1
1.2
1.3
2
Getting Started.....................................................................................1-1
Product Description............................................................................... 1-1
Pilot Controls........................................................................................... 2
USB Port.................................................................................................. 4
Basic Operation.....................................................................................2-1
2.1
COM Radio........................................................................................... 2-1
2.1.1
Selecting a COM Frequency.................................................... 2-1
2.1.2
Monitoring the Standby COM Channel.................................... 2-2
2.1.3
Saving a COM Channel........................................................... 2-2
2.1.4
COM Database Look-Up......................................................... 2-4
2.1.5
Emergency Channel................................................................ 2-5
2.1.6
Stuck Mic............................................................................... 2-5
2.1.7
Frequency Database Reverse Look-Up..................................... 2-5
2.1.8
Remote Frequency Selection Control....................................... 2-6
2.2 NAV Radio............................................................................................ 2-6
2.2.1
Selecting a NAV Frequency..................................................... 2-6
2.2.2
Saving a NAV Channel............................................................ 2-7
2.2.3
Listening to the NAV Audio Channel....................................... 2-8
2.3 OBS Mode............................................................................................ 2-8
2.4 Distance/Speed/Time (DST) Display........................................................ 2-9
3
Functions...............................................................................................3-1
3.1
3.2
Functions.............................................................................................. 3-1
COM Frequencies.................................................................................. 3-2
3.2.1
Recent COM Frequencies........................................................ 3-2
3.2.2
COM User Frequencies........................................................... 3-2
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.............. 3-6
3.2.6
COM Nearest Flight Service Station (FSS) Frequencies.............. 3-7
3.2.7
COM Nearest Weather (WX) Frequencies................................ 3-7
3.3 NAV Frequencies................................................................................... 3-8
3.3.1
Recent NAV Frequencies......................................................... 3-8
3.3.2
NAV User Frequencies............................................................ 3-8
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Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
3.3.3
NAV Database Frequencies................................................... 3-11
3.3.4
NAV Nearest VOR................................................................. 3-12
3.4 ICS Configuration............................................................................... 3-13
3.4.1
Adjust Intercom.................................................................... 3-13
3.4.2
AUX Audio........................................................................... 3-14
3.4.3
Intercom On/Off................................................................... 3-15
3.4.4
Speaker On/Off..................................................................... 3-15
3.5 System Configuration.......................................................................... 3-16
3.5.1
COM Spacing....................................................................... 3-16
3.5.2
COM Sidetone (Software v2.10 or later)................................ 3-17
3.5.3
Display Brightness................................................................ 3-18
3.5.4
Display Contrast................................................................... 3-19
3.5.5
Database Info....................................................................... 3-19
3.5.6
Load Database..................................................................... 3-20
3.5.7
Software Version.................................................................. 3-21
3.5.8
Serial Number...................................................................... 3-21
3.6 Timers................................................................................................ 3-22
3.6.1
Setting Up the Count Down Timer......................................... 3-22
3.6.2
Setting Up the Count Up Timer............................................. 3-22
3.6.3
Viewing Timers in the COM Display....................................... 3-23
4
4.1
4.2
5
5.1
DATABASE INFORMATION.....................................................................4-1
Downloading the Frequency Database................................................... 4-1
Updating the GNC 255 Frequency Database.......................................... 4-1
TROUBLESHOOTING..............................................................................5-1
Messages............................................................................................. 5-3
Index......................................................................................................Index-1
190-01182-01 Rev. C
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Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
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 fullfunctioned 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, built-in 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,
configuration for 8.33 kHz steps is provided with the GNC 255A (10 watt)
and GNC 255B (16 watt). 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.
Power On/Off,
COM Volume,
Squelch On/Off
Photo Sensor
Locking
Screw
Frequency Transfer
(FLIP/FLOP) Key
USB Port
Outer and
Inner Knobs
(Frequency
Adjust)
Enter Key
NAV (VLOC)
Volume, NAV
ID On/Off
Frequency
Monitor Key
COM or NAV
Frequency Selection
Clear Data Key
OBS Selection
Function Selection
To/From Selection
GNC 255 Front Panel Description
190-01182-01 Rev. C
Garmin GNC 255A/255B Pilot’s Guide
1-1-1
1.2 Pilot Controls
The GNC 255 controls are designed to simplify systems operation, minimize
workload, and reduce time required to access functionality. Controls are
comprised of dual concentric knobs for frequency tuning, COM volume/
squelch knob, NAV volume/ID knob, and bezel keys.
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. To power on, turn the knob
clockwise past detent. Turn the knob counterclockwise to 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
Standby Frequency
Annunciator
COM Volume and Squelch Display
The COM radio has an automatic squelch to reject many localized noise
sources. You may override the squelch function by pressing the Power/COM
Volume/Squelch knob. This facilitates listening to a distant station or setting
the desired volume level.
To override the automatic squelch, press the Power/COM Volume/Squelch
knob momentarily. Press the Power/COM Volume/Squelch knob again
to return to automatic squelch operation. When the automatic squelch is
overriden, an “SQ” indicator appears in the upper left corner of the display, left
of the active COM frequency window.
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Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
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.
The outer right and inner right knobs are used for tuning frequencies and data
entry.
Outer Knob
Inner Knob
To switch between the active (left-most) and standby (rightmost) frequency press and release the FLIP/FLOP key. Switching
between COM frequencies is disabled when transmitting.
To select the COM or NAV (VLOC) radio mode press the C/N
key.
To see the current OBS setting and graphic CDI press the OBS
key. The OBS page will be disabled if the unit is installed with an
external converter.
To toggle between the bearing TO or radial FROM the active
VOR press the T/F key. The T/F page also shows Distance/Speed/
Time information. The T/F key does not operate for Localizer
frequencies.
To erase information, cancel entries, or reset timers press the
CLR key.
To save selected values, to confirm a prompt, and to save the
standby frequency press the ENT key.
190-01182-01 Rev. C
Garmin GNC 255A/255B Pilot’s Guide
1-3
The FUNC (Function) key accesses function categories for
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.
The MON (Monitor) key engages the monitor function. The
standby frequency can 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: For updating the databases, Garmin recommends the use of a USB
2.0 compatible flash drive. The flash drive must be formatted as FAT32.
1-4
Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
2 BASIC OPERATION
2.1 COM Radio
2.1.1 Selecting a COM Frequency
New frequencies are first selected as a standby frequency and then toggled
to the active side with the FLIP/FLOP key. While viewing the standby
frequency display, use the outer and inner knobs on the right side of the
GNC 255 to select the desired frequency.
Identifier and Type
Asterisk Indicates Multiple Types
Exist For The Selected Frequency
COM Frequency Selection
1. Press C/N, if necessary, to reach the COM radio function. The COM
annunciator on the top line of the display will show.
2. Turn the outer knob to change the values in one MHz increments. The
MHz selection range is between 118 and 136 in one MHz steps.
3. Turn the inner knob to change the values in 25 kHz or 8.33 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.
4. Turn the outer and inner 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, the nearest station identifier will
be shown for the selected frequency. Frequencies with multiple types will
have an asterisk next to the identifier.
6. Press and release the FLIP/FLOP key to toggle the standby frequency to
the active frequency.
190-01182-01 Rev. C
Garmin GNC 255A/255B Pilot’s Guide
2-1
2.1.2 Monitoring the Standby COM Channel
Monitor
Annunciation
Monitored
Standby
Frequency
COM Frequency Monitor Annunciation
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.
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.
2.1.3 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 fifteen 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.
Number of Saved
Frequencies
COM User Frequency Name Selection
1. Press ENT.
2. Turn the inner knob to select characters.
3. Turn the outer knob to move the cursor.
4. After selecting characters, press ENT.
5. Turn the outer knob to select the waypoint type.
6. Turn the inner knob to select the type from the list.
7. Press ENT to save displayed value.
Press CLR to cancel the changes.
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Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
Waypoint Type
COM User Frequency Type Selection
COM Frequency Type List
Frequency Type Symbol
TWR
GND
ATIS
AWS
ATF
ARR
APPR
DEP
CLR
CTAF
FSS
RFS
MF
UNI
Blank
190-01182-01 Rev. C
Description
Tower
Ground
Automatic Terminal Information Service
Automated Weather Observing System
Aerodrome Traffic Frequency
Arrival
Approach
Departure
Clearance
Common Traffic Advisory Frequency
Flight Service Station
Remote Flight Service Station
Mandatory Frequency
Unicom
None
Garmin GNC 255A/255B Pilot’s Guide
2-3
2.1.4 COM Database Look-Up
1. Press the inner knob from the COM display to activate the database
look-up function.
Identifier Field
Character
Database Identifier Active for Selection
2. Turn the inner knob to select characters and turn the outer knob to move
the cursor.
Selected Identifier
Database Identifier Selection
3. After selecting characters, press ENT.
4. Turn the inner 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 stored for 30 minutes.
Turn Inner Knob to
Select Frequency Type
Database Waypoint Type Selection
5. Press ENT to copy the frequency into the standby frequency location.
6. The nearest station identifier will show for the selected frequency if
connected to a GPS position source.
7. Press and release the FLIP/FLOP key to swap the active and standby
frequencies.
2-4
Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
2.1.5 Emergency Channel
Press and hold the FLIP/FLOP key or the COM Remote Transfer (COM RMT
XFR) key for approximately two seconds. The Emergency Channel will be
inserted into the active frequency position and the previous active Frequency
will become the standby frequency.
Emergency Channel
NOTE: Pressing and holding the COM Remote Transfer (COM RMT XFR)
key for approximately two seconds, on units so configured, will lock the
COM board, preventing further changes in COM frequency until the COM
board is unlocked, by pressing the COM Remote Transfer key again for two
seconds. The following message will notify the pilot that the COM board
has been locked: “COM LOCKED TO 121.5 MHZ. HOLD REMOTE COM
TRANSFER KEY TO EXIT.”
NOTE: Under some circumstances if the COM system loses communication
with the main system, the radio will automatically tune to 121.50 MHz for
transmit and receive regardless of the displayed frequency.
2.1.6 Stuck Mic
The GNC 255 helps protect you from a situation where the microphone may
get stuck in the ON or Transmit position. If the microphone is keyed for longer
than 35 seconds, the GNC 255 will return to the receive mode on the selected
frequency.
A “Stuck Mic” message will display until the transmit key is released. Alerts
will display until the error clears or the user acknowledges it.
2.1.7 Frequency Database Reverse Look-Up
When the unit is receiving a valid position input, the identifier and frequency
type will show for COM and NAV frequencies for the nearest facilities.
Waypoint types with a “+” sign will have more frequencies for the same type.
Airport Identifier Shown For
Frequencies In Database
Frequency Database Reverse Look-Up
190-01182-01 Rev. C
Garmin GNC 255A/255B Pilot’s Guide
2-5
2.1.8 Remote Frequency Selection Control
On units configured for remote COM frequency recall, pressing the remote
recall switch will load the next preset COM frequency into the unit’s standby
frequency box. The remote recall switch can be pressed multiple times to scroll
the entire preset frequency list through the standby frequency box (the list will
wrap from the bottom of the list back up to the top, skipping any empty preset
positions).
The standby frequency isn’t activated until either the bezel-mounted COM
FLIP/FLOP key or remote COM RMT XFR switch is pressed. Remote
Frequency Selection only functions on units configured for a remote COM
Frequency recall switch.
2.2 NAV Radio
2.2.1 Selecting a NAV Frequency
The selection of NAV frequencies is the same as for the COM frequencies.
1. Press the C/N key to reach the NAV radio function. The NAV annunciator
on the top line of the display will show.
2. Turn the outer knob to change the MHz values. The MHz selection range
is between 118 and 136 in one MHz steps.
3. Turn the inner knob to change the kHz values.
Identifier and Type Shown For
The Selected Frequency
NAV Frequency Selection
CAUTION: The Identifier is determined from the database and is not the
decoded NAV Identifier.
4. Press and release the FLIP/FLOP key to toggle the standby frequency to
the active frequency.
NOTE: Both NAV and COM frequencies cannot be displayed at the same
time.
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Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
2.2.2 Saving a NAV Channel
The current standby frequency may be saved into the NAV User Frequency
database from the NAV or the NAV User Function. The NAV User Frequency
database can hold up to fifteen frequencies.
1. Press ENT.
2. Turn the inner knob to select characters.
3. Turn the outer knob to move the cursor.
NAV User Frequency Name Selection
4. After selecting characters, press ENT.
5. Turn the outer knob to select the waypoint type.
6. Turn the inner knob to select the type from the list.
NAV User Frequency Type Selection
7. Press ENT to save displayed values.
Press CLR to cancel the changes.
NAV Frequency Type List
Frequency Type Symbol
VOR
DME
LOC
ILS
01-36
Blank
190-01182-01 Rev. C
Description
Very High Frequency Omni-Directional Range
Distance Measuring Equipment
Localizer
Instrument Landing System
Runway Heading
None
Garmin GNC 255A/255B Pilot’s Guide
2-7
2.2.3 Listening to the NAV Audio Channel
NAV ident is enabled by pressing the NAV Volume knob when the NAV
display is active. When NAV ident is enabled, the ID annunciation will appear
to the left of the active NAV frequency.
Listening to the ID for a NAV Frequency
NAV audio volume is adjusted using the NAV Volume knob. Turn the NAV
Volume knob clockwise to increase volume, or counterclockwise to decrease
volume.
2.3 OBS Mode
There are four different CDI configurations, which allow the installer to
configure the GNC 255 to the type of CDI indicator that is connected. The
installer-set CDI configuration will determine the operation of the OBS Mode.
If the system is configured with an analog or digital external CDI/HSI, the OBS
radial of the remote display will be decoded and displayed on the screen of the
GNC 255.
Press the OBS key to see the current OBS setting and graphic CDI.
NOTE: The Identifier is the decoded NAV identifier from the Morse code
broadcast by the station.
If the system is configured with a composite external indicator, the OBS mode
will be unavailable. If there is no external CDI/HSI providing OBS control, the
outer and inner knobs can be used to change the displayed OBS value.
The GNC 255 graphic CDI is shown as a graph of five dots right or left of the
triangle icon. Each dot indicates two degrees deflection with ten degrees full
deflection to each side. Fly towards the bar to be on-course.
Active NAV
Frequency
Reference COM
Frequency
Identifier
OBS Setting
To/From Indication for
Selected Station
CDI Deflection
CDI Display
2-8
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2.4 Distance/Speed/Time (DST) Display
When the GNC 255 has received data from a GPS receiver or DME sensor
through the serial port, DST data will be available. If the GNC 255 is not
connected to an external sensor, this display will not be available.
If DST data is not shown, press the T/F key to show DST data in the lower part
of the display.
Station Identifier
Bearing To/From Station
Active NAV Frequency
Time To Station In
Hours and Minutes
Distance To Station
In Nautical Miles
Ground Speed From
GPS Unit In Knots
DST Data Display
NOTE: The If both GPS and DME data sources are connected to the GNC
and dashes are displayed when distance/speed/time data is expected to
be displayed, press the T/F key to prompt the GNC to display DST data.
NOTE: DST information will only be displayed for stations that are within
200 NM.
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3 FUNCTIONS
Information about COM Frequencies, NAV Frequencies, ICS Configuration,
SYS Configuration, and Timer Configuration is provided in this section.
3.1 Functions
COM
Frequency
List
NAV
Frequency
List
ICS
Configuration
SYS
Configuration
TMR
Configuration
Recent Freqs
User Freqs
Database
Nearest Apt
Nearest ACC
Nearest FSS
Nearest WX
Recent Freqs
User Freqs
Database
Nearest VOR
Adjust Intrcom
Aux Audio
Intrcom On/Off
Speaker On/Off
COM Spacing
COM Sidetone
DSPL Brt
DSPL Contrast
Database Info
Load Database
Software Ver
Serial Number
Count Down
ENT - Start/Stop
CLR - Reset
Push CRSR - Settings
ENT - Accept
Count Up
ENT - Start/Stop
CLR - Reset
Functions Diagram
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3-1
3.2 COM Frequencies
The COM Frequency List contains recently used frequencies (Recent), userdefined frequencies (User), a database of all frequencies provided in the
standard default memory (Database), and nearest airport, Area Control Center
(ACC), Flight Service Station (FSS), and weather frequencies (WX).
3.2.1 Recent COM Frequencies
The last twenty COM frequencies used are kept in the list of recent COM
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.
Entry
Selected Frequency
Recent COM Frequencies
1. Press FUNC.
2. Turn the inner knob to RECENT FREQS.
3. Press ENT.
4. Turn the inner knob to select an entry (1-20).
5. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the selected frequency as the standby frequency.
3.2.2 COM User Frequencies
Fifteen COM user frequencies can be saved with an assigned waypoint (WPT)
identifier and type.
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.
Frequency
Waypoint Type
Waypoint Name
COM User Frequencies
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Viewing a COM User Frequency
1. Press FUNC.
2. Turn the inner knob to USER FREQS.
3. Press ENT.
4. Turn the inner knob to cycle through COM user frequencies.
5. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the selected frequency as the standby frequency.
Deleting a COM User Frequency
Position In List
Active Frequency
Deleting User COM Frequencies
1. Press FUNC.
2. Turn the inner knob to USER FREQS.
3. Press ENT.
4. Turn the inner knob to cycle through COM user frequencies.
5. Press CLR to delete selected frequency.
6. Press ENT to confirm selection.
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Editing a COM User Frequency
User Frequency
COM User Frequency Selection
1. Press FUNC.
2. Turn the inner knob to USER FREQS.
3. Press ENT.
4. Turn the inner knob to the COM user frequency to edit.
5. Press the inner knob to start editing the COM user frequency.
6. Turn the inner knob to select the MHz values.
7. Turn the outer knob to select the kHz field.
8. Turn the inner knob to select the kHz values.
9. Turn the outer knob to select the WPT field.
10. Turn the inner knob to select characters and turn the outer knob to move
the cursor.
Waypoint Name
COM User Frequency Name Selection
11. Press ENT.
12. Turn the outer knob to select the TYPE field.
13. Turn the inner knob to select the waypoint type.
Waypoint Type
COM User Frequency Type Selection
14. Press ENT to accept changes.
Press CLR to cancel changes.
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3.2.3 COM Database Frequencies
The GNC 255 contains a database of COM frequencies that may be recalled by
identifier.
Character
COM Database Frequencies
1. Press FUNC.
2. Turn the inner knob to DATABASE.
3. Press ENT.
4. Turn the inner knob to select the character.
5. Turn the outer knob to move the cursor to highlight a character.
6. Press ENT.
7. If the frequency type is available, turn the inner knob to select the
frequency type.
8. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the selected frequency as the standby frequency.
NOTE: The nearest station identifier for the selected frequency will be
shown below the active or standby frequency, when connected to a GPS
position source.
Frequency
Frequency Type
Waypoint Identifier
Selected COM Database Frequency
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3.2.4 COM Nearest Airports (APT)
When interfaced with a GPS receiver, the GNC 255 will report the twenty-five
nearest airports (APT).
Available Airports
COM Nearest Airport Frequencies
1. Press FUNC.
2. Turn the inner knob to NEAREST APT.
3. Press ENT.
4. Turn the inner knob to scroll through the list of available APT frequencies.
5. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the selected frequency as the standby frequency.
Press CLR to return to the functions display.
3.2.5 COM Nearest Area Control Center (ACC)
Frequencies
When interfaced with a GPS receiver, the GNC 255 will report the twenty-five
nearest Area Control Center (ACC) frequencies. ACCs are also known as Air
Route Traffic Control Centers (ARTCC).
Available ACC Frequencies
COM Nearest Area Control Center Frequencies
1. Press FUNC.
2. Turn the inner knob to NEAREST ACC.
3. Press ENT.
4. Turn the inner knob to scroll through the list of available ACC frequencies.
5. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the selected frequency as the standby frequency.
Press CLR to return to the functions display.
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3.2.6 COM Nearest Flight Service Station (FSS)
Frequencies
When interfaced with a GPS receiver, the GNC 255 will report the twenty-five
nearest Flight Service Station (FSS) frequencies.
Available FSS
Frequencies
COM Nearest Flight Service Station Frequencies
1. Press FUNC.
2. Turn the inner knob to NEAREST FSS.
3. Press ENT.
4. Turn the inner knob to scroll through the list of available FSS frequencies.
5. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the selected frequency as the standby frequency.
Press CLR to return to the functions display.
3.2.7 COM Nearest Weather (WX) Frequencies
When interfaced with a GPS receiver, the GNC 255 will report the twenty-five
nearest weather (WX) frequencies.
Available Frequencies
COM Nearest Weather Frequencies
1. Press FUNC.
2. Turn the inner knob to NEAREST WX.
3. Press ENT.
4. Turn the inner knob to scroll through the list of available weather
frequencies.
5. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the selected frequency as the standby frequency.
Press CLR to return to the functions display.
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3.3 NAV Frequencies
The NAV Frequencies list contains recently used frequencies (Recent), userdefined frequencies (User), a database of all frequencies provided in the
standard default memory (Database), and nearest VOR frequencies.
3.3.1 Recent NAV Frequencies
The last twenty NAV frequencies used are kept in the list of recent NAV
frequencies.
1. Press FUNC.
2. Turn the outer knob to NAV FREQUENCY LIST.
3. Turn the inner knob to RECENT FREQS.
4. Press ENT.
Active
Frequency
List Entry
Selected Frequency
Recent NAV Frequencies
5. Turn the inner knob to select an entry (1-20).
6. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the displayed frequency as the standby frequency.
3.3.2 NAV User Frequencies
Fifteen NAV user frequencies can be saved with an assigned waypoint (WPT)
identifier and type.
Active
Frequency
Position In List
Selected Frequency
Viewing User NAV Frequencies
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Viewing a NAV User Frequency
1. Press FUNC.
2. Turn the outer knob to NAV FREQUENCY LIST.
3. Turn the inner knob to USER FREQS.
4. Press ENT.
5. Turn the inner knob to view the NAV user frequencies.
6. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the displayed frequency as the standby frequency.
Deleting a NAV User Frequency
Active
Frequency
Position In List
Deleting User NAV Frequencies
1. Press FUNC.
2. Turn the outer knob to NAV FREQUENCY LIST.
3. Turn the inner knob to USER FREQS.
4. Press ENT.
5. Turn the inner knob to cycle through NAV user frequencies.
6. Press the CLR key to delete the selected user frequency.
7. Press ENT to confirm deleting the selection.
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Editing a NAV User Frequency
Waypoint Type
Waypoint Name
NAV User Frequency Name and Type Selection
1. Press FUNC.
2. Turn the outer knob to NAV FREQUENCY LIST.
3. Turn the inner knob to USER FREQS.
4. Press ENT.
5. Turn the inner knob to the NAV user frequency to edit.
6. Press the inner knob to start editing NAV user frequency.
7. Turn the inner knob to select the MHz values.
8. Turn the outer knob to select the kHz field.
9. Turn the inner knob to select the kHz values.
10. Turn the outer knob to select the WPT field.
11. Turn the inner knob to select characters and turn the outer knob to move
the cursor.
12. Press ENT.
13. Turn the outer knob to select the TYPE field.
14. Turn the inner knob to select the waypoint type.
15. Press ENT to accept changes.
Press CLR to cancel changes.
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3.3.3 NAV Database Frequencies
The GNC 255 contains a database of NAV frequencies that may be recalled by
identifier.
Character
NAV Database Frequencies
1. Press FUNC.
2. Turn the outer knob to NAV FREQUENCY LIST.
3. Turn the inner knob to DATABASE.
4. Press ENT.
5. Turn the inner knob to select the character.
6. Turn the outer knob to move the cursor to highlight a character.
7. Press ENT.
8. If the frequency type is available, turn the inner knob to select the
frequency type.
9. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the selected frequency as the standby frequency.
Frequency
Waypoint Identifier
Frequency Type
Selected NAV Database Frequency
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Duplicate Identifiers
1. When duplicate identifiers are found, press ENT.
Duplicate Identifiers
Found
Selected NAV Database Frequency
2. Turn the inner knob to select the identifier.
3. Press ENT.
Selected Ident from NAV Database
4. Press FLIP/FLOP to set the selected frequency as the active frequency.
Press ENT to set the displayed frequency as the standby frequency.
Selected Frequency
Wpt Type
Selected Identifier
Set Selected Frequency as Active or Standby
3.3.4 NAV Nearest VOR
When interfaced with a GPS receiver, the GNC 255 will report the twenty five
nearest VORs.
List of Available VORs
NAV Nearest VOR Frequencies
1. Press FUNC.
2. Turn the outer knob to NAV FREQUENCY LIST.
3. Turn the inner knob to NEAREST VOR.
4. Press ENT.
5. Turn the inner knob to display the available VORs.
6. Press ENT to set the displayed VOR frequency as standby.
Press CLR to exit without changes.
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3.4 ICS Configuration
ICS Configuration adjusts the intercom, sets the NAV/AUX volume, and turns
the intercom and speaker on or off.
3.4.1 Adjust Intercom
The Adjust Intercom function sets the values for the intercom squelch,
intercom volume, and sets the intercom audio to mute when COM
transmissions are received. The Intercom On/Off function must be set to ON to
make the Adjust Intercom function available.
NOTE: To enable ICS auto squelch, turn the knob one click counterclockwise
past 0. When squelch is set to auto, the squelch sensitivity adjusts
automatically. When squelch is set to 0, squelch is usually open. When
squelch is set to 100, squelch is usually closed. ICS auto squelch is available
with software v2.10 or later.
Intercom Squelch
Intercom Volume
Mute On RX
Adjust the Intercom Settings
1. Press FUNC.
2. Turn the outer knob to ICS CONFIGURATION.
3. Turn the inner knob to ADJUST INTRCOM.
4. Press ENT.
5. Turn the inner knob to set the ICS squelch (SQ).
6. Turn the outer knob to move to ICS volume (VOL) field.
7. Turn the inner knob to set the ICS volume level.
8. Turn outer knob to MUTE ON RX (software v2.10 or later).
9. Turn the inner knob to ON or OFF. To mute when a radio transmission is
received, select ON.
10. Press ENT to save changes.
Press CLR to cancel the changes.
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3.4.2 AUX Audio
The AUX Audio function turns AUX Audio on or off, sets the AUX volume
level, and sets the AUX audio to mute when a COM radio transmission is
received.
AUX Audio Status
AUX Audio Volume
Adjust AUX Audio
1. Press FUNC.
2. Turn the outer knob to ICS CONFIGURATION.
3. Turn the inner knob to AUX AUDIO.
4. Press ENT.
5. Turn the inner knob to turn the AUX audio ON or OFF.
6. Turn the outer knob to VOL.
7. Turn the inner knob to set the AUX volume level.
8. Turn the outer knob to MUTE ON RX (available with software v2.10 or
later).
9. Turn the inner knob to ON or OFF. To mute the AUX audio when a radio
transmission is received, select ON.
10. Press ENT to save new values.
Press CLR to cancel the changes.
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3.4.3 Intercom On/Off
The Intercom On/Off fuction toggles the intercom on or off. If installed with
a remote switch, the intercom can also be remotely toggled on or off. The
Intercom On/Off function must be set to ON to make the Adjust Intercom
function available.
Intercom On or Off
Intercom On/Off
1. Press FUNC.
2. Turn the outer knob to ICS CONFIGURATION.
3. Turn the inner knob to INTRCOM ON/OFF.
4. Press ENT.
5. Turn the inner knob to set the intercom ON or OFF.
6. Press ENT to save the selected value.
Press CLR to cancel the change.
3.4.4 Speaker On/Off
Speaker On or Off
Speaker On/Off
1. Press FUNC.
2. Turn the outer knob to ICS CONFIGURATION.
3. Turn the inner knob to SPEAKER ON/OFF.
4. Press ENT.
5. Turn the inner knob to set the speaker output ON or OFF.
6. Press ENT to save the selected value.
Press CLR to cancel the change.
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3.5 System Configuration
The System Configuration function displays the software version, database
information, and serial number. This information is helpful when contacting
customer support. It also allows setting the COM spacing, display brightness
and contrast, and to update databases.
3.5.1 COM Spacing
COM spacing may be selected between 8.33 kHz and 25 kHz to allow for
regional requirements.
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.
Channel Spacing
COM Spacing Display
1. Press FUNC.
2. Turn the outer knob to SYS CONFIGURATION.
3. Turn the inner knob to COM SPACING.
4. Press ENT.
5. Turn the inner knob to set the COM spacing.
6. Press ENT to save the selected value.
Press CLR to cancel the change.
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3.5.2 COM Sidetone (Software v2.10 or later)
COM sidetone is the audio spoken into the COM microphone. This setting
affects the volume of the sidetone in the headsets for the COM during PTT.
The COM Sidetone Offset adjusts the amount that the COM sidetone volume
level is offset from the COM receiver volume level. The range can be adjusted
from -10 (lowest) to 10 (highest), with 0 as the default.
NOTE: COM sidetone pilot control must be enabled by the installer.
Offset Mode
Offset Value
COM Sidetone Page
1. Press FUNC.
2. Turn the outer knob to SYS CONFIGURATION.
3. Turn the inner knob to COM SIDETONE.
4. Press ENT.
5. Turn the inner knob to set mode of COM sidetone.
OFFSET: COM sidetone volume changes with adjustments of the COM
volume knob.
FIXED: COM sidetone volume is at level set at installation.
6. If offset mode is selected, turn the outer knob to OFFSET.
7. Turn the inner knob to set the offset value.
8. Press ENT to save selected values.
Press CLR to cancel the changes.
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3.5.3 Display Brightness
From the factory, the GNC 255 automatically adjusts its display brightness for
the current lighting conditions. A small sensor on the display is used for this
function. A manual adjustment is available for controlling the brightness level
of the display as an offset from the normal or zero position.
The limits of the adjustment range are: -10 (Low Display Intensity) and 100
(High Display Intensity). A value above zero means brighter than normal and
a value below zero means darker than normal. The range can be adjusted by
using the inner knob.
The GNC 255 will either control dimming based on the photocell or the
lighting bus. This is set in configuration mode during installation and is not
selectable by the pilot.
Current Display Brightness
Offset Value
Display Brightness Page
1. Press FUNC.
2. Turn the outer knob to SYS CONFIGURATION.
3. Turn the inner knob to DSPL BRT.
4. Press ENT.
5. Turn the inner knob to set the value.
6. Press ENT to save selected value.
Press CLR to cancel change.
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3.5.4 Display Contrast
The display contrast has a range from -50 (low) and 50 (high) with 0 as the
default. The range can be adjusted by using the inner knob.
Offset Value
Display Contrast Page
1. Press FUNC.
2. Turn the outer knob to SYS CONFIGURATION.
3. Turn the inner knob to DSPL CONTRAST.
4. Press ENT.
5. Turn the inner knob to set the offset value.
6. Press ENT to save selected value.
Press CLR to cancel change.
3.5.5 Database Info
Database Cycle
Database Effectivity Date
Database Info Page
1. Press FUNC.
2. Turn the outer knob to SYS CONFIGURATION.
3. Turn the inner knob to DATABASE INFO.
4. Press ENT.
5. Press FUNC to exit page.
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3.5.6 Load Database
The GNC 255 has a USB port to allow for easily updating the system
databases.
NOTE: Garmin recommends the use of a USB 2.0 compatible USB flash
drive, formatted as FAT32, for updating the database.
USB Port
USB Cable
USB Flash Drive
1. Insert the supplied cable into the USB port of the unit.
2. Insert the USB flash drive into the other end of the cable.
3. Press FUNC.
4. Turn the outer knob to SYS CONFIGURATION.
5. Turn the inner knob to LOAD DATABASE.
6. Press ENT.
Database Update Page
7. Verify the database version on flash drive.
Version On Unit
Version On Flash Drive
Database Version Page
8. Press ENT to begin update.
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9. Wait until the updating process is complete, then verify the correct
database is loaded onto the unit.
3.5.7 Software Version
Display Software Version
COM Software Version
NAV Software Version
Software Versions Page
1.
Press FUNC.
2.
Turn the outer knob to SYS CONFIGURATION.
3.
Turn the inner knob to SOFTWARE VER.
4.
Press ENT.
5.
Press FUNC to return to the main menu.
3.5.8 Serial Number
NOTE: The ID consists of a combination of numbers 0-9 and letters A-F.
The number 8 and the letter B are distinguishable as depicted in the Serial
Number screenshot.
Unit Serial Number
ID Is Used With The
flyGarmin Services
8 B
Serial Number Page
1. Press FUNC.
2. Turn the outer knob to SYS CONFIGURATION.
3. Turn the inner knob to SERIAL NUMBER.
4. Press ENT.
5. Press FUNC to return to the main menu.
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3.6 Timers
The GNC 255 has both count up and count down timers, which may operate
simultaneously, and are shown in the lower right of the COM/NAV displays.
The countdown timer always takes precedence if it is running.
3.6.1 Setting Up the Count Down Timer
Default Start Time
Minutes
Hours
Seconds
Count Down Timer Page
1. Press FUNC.
2. Turn the outer knob to TMR CONFIGURATION.
3. Turn the inner knob to COUNT DOWN.
4. Press ENT.
5. Press the inner knob to enter a starting timer value.
6. Turn the outer knob to move to set seconds, minutes, or hours.
7. Press ENT to confirm entry.
8. Press ENT to start or stop the timer.
9. Press the CLR key to reset the timer to the starting value.
10. Press the inner knob to change the starting timer value.
3.6.2 Setting Up the Count Up Timer
The Default (Starting) Value
Count Up Timer Page
1. Press FUNC.
2. Turn the outer knob to TMR CONFIGURATION.
3. Turn the inner knob to COUNT UP.
4. Press ENT.
5. Press the ENT key to start the timer.
6. Press the ENT key again to stop the timer.
7. Press CLR to reset the timer to 0:00 and stop counting.
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3.6.3 Viewing Timers in the COM Display
When a timer is active, the timer value will be shown in the lower right corner
of the COM display. While both timers may be actively counting at the same
time, the count down timer will have precedence in being shown. If the count
down timer is paused, the count up timer will then be shown until the count
down timer is restarted.
Timer Value
Timer Value Shown in the COM Display
Clearing and Stopping Displayed Timers
Clearing and Stopping Timers
1. To reset timer, press CLR and then ENT.
2. To stop the displayed timer, press ENT twice.
When the Count Down Timer reaches 0:00, it will continue counting as
a count up timer. The count down timer, which is counting up, will be
highlighted. A count up timer will continue counting separately.
Count Down Timer Value
Highlighted When Counting Up
COM Display with Count Down Timer Now Counting Up
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4 DATABASE INFORMATION
NOTE: The data contained in the frequency database comes from
government agencies. Garmin accurately processes and cross-validates the
data, but cannot guarantee the accuracy and completeness of the data.
The GNC 255 uses a standard USB flash drive to load the frequency database
into the GNC 255. The flash drive is not provided by Garmin. The frequency
database is stored internally and the USB flash drive is only used to transfer the
database into the unit.
The following equipment is required to perform the update:
• Windows-compatible PC computer (Windows 2000, XP, Vista, or
Windows 7 recommended)
• USB 2.0 compatible USB flash drive formatted as FAT32.
• External USB cable
• Updated database obtained from the Garmin website
4.1 Downloading the Frequency Database
NOTE: The GNC 255’s system ID is required when downloading the
Frequency database. See section 3.5.8 for details on the system ID.
The Garmin databases can be updated by following the instructions on
https://fly.garmin.com/fly-garmin. The frequency database is updated on 28-day
cycle.
4.2 Updating the GNC 255 Frequency Database
See section 3.5.6 for details on loading the database into the GNC 255.
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5 TROUBLESHOOTING
If efforts to resolve the problem are not successful, contact your dealer or the
factory for technical assistance. Please have the following information ready:
• System configuration (products, antennas, mounting locations, etc.)
• Model number, part number, and serial number
• Software versions
• Description of the problem
• Efforts made to isolate/solve the problem
Garmin International, Inc.
Aviation Products Customer Service Department
1200 East 151st Street
Olathe, KS 66062-3426 USA
If you have any questions, the Garmin Product Support department may be
reached Monday through Friday, 7:00 AM to 7:00 PM CT.
US: 913-397-8200
US Toll Free: 1-866-739-5687
Canada Toll Free: 1-866-429-9296
Email: support.gat@garmin.com
http://www.garmin.com
https://fly.garmin.com/fly-garmin
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5-1
Troubleshooting
Problem
GNC 255 does not power on
Possible Cause
No power to the
GNC 255
Faulty electrical
wiring or connection
No NAV audio
NAV audio in COM
GNC 255 does not transmit
Intercom doesn’t function
Unable to change active
frequency
OBS readout displays “---”
5-2
Output disabled or
set to a low level
Mixed with COM
feature
No power to COM
Mic key connection
It can be enabled
or disabled via a
remote mounted
switch or via the
menu.
No voice activation,
or if must talk too
loud
COM Radio not
communicating. The
radio may also be in
lockout mode. In this
case the radio would
be tuned to 121.50
and the active freq
would not be able to
be changed.
Resolver failure
Calibration error
Garmin GNC 255A/255B Pilot’s Guide
Action
Check power connections,
breakers, and main
avionics switch
Contact your dealer to
perform electrical system
test
Contact dealer
Contact dealer
Check power connections
Check Mic key input
connection
Check connections
Check ICS page, Intercom
On/Off, Adjust Intercom
If in Lock Out mode,
press the external COM
FLIP/FLOP key for two
seconds to return to
normal operation or cycle
the avionics power. If the
condition persists, contact
dealer.
Contact dealer
Recalibrate resolver
190-01182-01 Rev. C
Problem
Display shows
“Incorrect Calibration
Checksum” at start-up
Possible Cause
Corrupted system
calibration
parameters
Action
Contact factory
5.1 Messages
When a message has been issued by the unit, the message will be shown on
the display. After viewing the messages, press the ENT key to acknowledge the
message and return to the previously viewed page. An acknowledged message
will not be redisplayed even if the condition persists. Messages provide an aid
to troubleshooting system operation.
Message
Display of Message
Messages
Message
COM RADIO COM radio needs
service.
Description
The COM radio is
reporting that it needs
service. The COM
radio may continue to
function.
The COM radio is not
COM RADIO COM radio may be communicating properly
with the system.
inoperative.
COM RADIO COM overtemp
or undervoltage.
Reducing
transmitter power.
190-01182-01 Rev. C
Action
Cycle the power to the COM radio.
Contact dealer for service.
Press and hold the volume knob or
the external COM remote transfer
(COM RMT XFR) switch, if installed
– this will force the COM radio
to 121.5 MHz. Contact dealer for
service.
COM radio is
Decrease length of COM
in overtemp or
transmissions, decrease cabin
undervoltage mode
temperature and increase cabin
and transmitting power airflow (especially near the GNC).
has been reduced to
Check aircraft voltage and reduce
prevent damage to the electrical load as necessary.
COM radio. Radio range Contact dealer for service if this
will be reduced.
message persists.
Garmin GNC 255A/255B Pilot’s Guide
5-3
Message
Description
COM radio is locked to
COM RADIO 121.5 MHz.
COM locked to
121.5 MHz. Hold
remote COM
transfer key to exit.
COOLING FAN - The GTN cooling fan is
The cooling fan has powered, but it is not
turning at the desired
failed.
RPM.
DISPLAY Display board
needs service.
FEATURE
UNLOCK
FAILURE
The display board is
indicating that it needs
service.
The database on the
USB flash drive is
corrupt or the system
ID in the database does
not match the unit’s
system ID.
The glideslope board is
GLIDESLOPE Glideslope receiver indicating that it needs
service. The glideslope
needs service.
board may continue to
function.
The glideslope board
GLIDESLOPE Glideslope receiver is not communicating
property with the
has failed.
system.
5-4
Action
The external COM remote transfer
(COM RMT XFR) switch has been
held and the COM radio is tuned
to 121.5. To exit this mode, hold
the COM remote transfer (COM
RMT XFR) switch for two seconds.
Decrease cabin temperature and
increase cabin airflow (especially
near the GTN) to prevent damage
to the unit. Contact dealer for
service.
Contact dealer for service.
Verify that the correct system ID
is entered into flyGarmin.com
when downloading the database.
Contact Garmin Customer Support
if this message persists.
Verify glideslope deviation
indications with another source
and crosscheck final approach
fix crossing altitude. If another
glideslope source is not available
for verification, fly a GPS based
approach. Contact dealer for
service.
Fly an approach that does not use
the glideslope receiver (VOR, LOC,
GPS). Contact dealer for service.
Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
Message
Description
NO UNLOCK FILE The USB flash drive
is missing the feature
unlock file for the
frequency database.
Action
Verify that the correct system ID
is entered on flyGarmin.com and
that the frequency database is
downloaded onto the USB flash
drive. Contact Garmin Customer
Support if this message persists.
NOTE: The GNC 255’s system ID is required when downloading the
frequency database. See section 3.4.8 for details on the system ID.
POWER ALERT Unit will shut down
if power switch
is not restored
immediately.
REMOTE KEY
STUCK COM push-to-talk
key is stuck.
REMOTE KEY
STUCK COM remote
transfer key is
stuck.
190-01182-01 Rev. C
Power has been
removed from the unit.
Re-apply power to the unit.
The Push To Talk key
or switch has been in
pressed position for
at least 30 seconds.
This input will now be
ignored and the COM
radio will no longer
transmit.
The remote COM
transfer (COM RMT
XFR) key or switch
has been in pressed
position for at least 30
seconds. This input will
now be ignored. This
input is not available in
all installations.
Verify the Push To Talk key or
switch is not stuck. Contact dealer
for service if this message persists.
Verify the COM RMT XFR key or
switch is not stuck. Contact dealer
for service if this message persists.
Garmin GNC 255A/255B Pilot’s Guide
5-5
Message
REMOTE KEY
STUCK COM remote
frequency
increment key is
stuck.
Description
The remote COM
frequency increment
(COM CHAN UP) key
or switch has been in
pressed position for
at least 30 seconds.
This input will now
be ignored. This input
is not available in all
installations.
The remote COM
REMOTE KEY
frequency decrement
STUCK (COM CHAN DN) key
COM remote
or switch has been in
frequency
pressed position for
decrement key is
at least 30 seconds.
stuck.
This input will now
be ignored. This input
is not available in all
installations.
The remote NAV
REMOTE KEY
transfer (NAV RMT XFR)
STUCK key or switch has been
NAV remote
in pressed position for
transfer key is
at least 30 seconds.
stuck.
This input will now
be ignored. This input
is not available in all
installations.
VLOC RECEIVER - The NAV radio is
Navigation receiver reporting that it needs
service. The NAV
needs service.
radio may continue to
function.
5-6
Action
Verify the COM CHAN UP key or
switch is not stuck. Contact dealer
for service if this message persists.
Verify the COM CHAN DN key or
switch is not stuck. Contact dealer
for service if this message persists.
Verify the NAV RMT XFR key or
switch is not stuck. Contact dealer
for service if this message persists.
Contact dealer for service.
Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
Message
Description
VLOC RECEIVER - The NAV radio is
Navigation receiver not communicating
property with the
has failed.
system.
190-01182-01 Rev. C
Action
Contact dealer for service.
Garmin GNC 255A/255B Pilot’s Guide
5-7
This page intentionally left blank
5-8
Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
INDEX
G
Getting started 1-1
A
I
AUX Audio 3-14
ICS 3-13
Intercom 3-15
B
Basic operation 2-1
Brightness 3-18
K
Knobs 3
C
Cautions ii, 2-6
CLR key 1-3
C/N key 1-3
COM database frequencies 3-5, 3-6, 3-7
COM frequencies 3-2
COM PTT 3-16
COM radio 2-1
COM select frequency 2-1
COM sidetone 3-17
COM spacing 3-16
COM user frequencies 3-2
COM volume 1-2
Contrast 3-19
Controls 1-2
Customer service i
D
Database frequencies 3-5, 3-11
Database Information 4-1
Database look-up 2-4
Display brightness 3-18
DST 2-9
Duplicate identifiers 3-12
E
Emergency channel 2-5
ENT key 1-3
F
Flight Service Station 3-7
FLIP/FLOP key 1-3
Fly.Garmin iv, 5-1
Frequency monitoring 2-2
Front panel description 1-1
FSS 3-7
FUNC key 1-4
190-01182-01 Rev. C
L
Locking screw 1-1
M
Message 5-3
Monitoring 2-2
MON key 1-4
Morse code 1-1
N
NAV audio 2-8
NAV database frequencies 3-11
NAV frequencies 3-8
NAV ID 1-3
NAV radio 2-6
NAV frequency select 2-6
NAV user frequencies 3-8
NAV volume 1-3, 2-3
Nearest airport 3-6
O
OBS key 1-3
OBS mode 2-8
P
Pilot controls 1-2
Product description 1-1
Product Support iv, 5-1
R
Recent COM frequencies 3-2
Recent NAV frequencies 3-8
Record of Revisions v
Registration iv
Remote frequency control 2-6
Reverse look-up 2-5
Revisions v
Garmin GNC 255A/255B Pilot’s Guide
Index-1
S
Saving a COM channel 2-2
Saving a NAV channel 2-7
Serial Number 3-21
Software version 3-21
Speaker On/Off 3-15
Squelch 1-2
Stuck mic 2-5
Support iv
System configuration 3-16
T
T/F key 1-3
Timers 3-22
Troubleshooting 5-3
U
Updating frequency database 4-1
USB 1-4, 3-20
User frequencies 3-2, 3-8
V
Volume 1-2
W
Warranty i
Index-2
Garmin GNC 255A/255B Pilot’s Guide
190-01182-01 Rev. C
© 2012-2015 Garmin Corporation
Garmin International, Inc.
1200 East 151st Street, Olathe, Kansas 66062, U.S.A.
Tel. 913/397.8200 or 866/739.5687
Fax 913/397.8282
Garmin AT, Inc.
2345 Turner Rd., S.E., Salem, Oregon 97302, U.S.A.
Tel. 503/581.8101 or 800/525.6726
Fax. 503/364.2138
Garmin (Europe) Ltd.
Liberty House, Bulls Copse Road, Hounsdown Business Park,
Southampton, SO40 9LR, U.K.
Tel. +44 (0) 87 0850 1243
Fax +44 (0) 23 8052 4004
Garmin Singapore Pte. Ltd.
46 East Coast Road
#05-06 Eastgate
Singapore 428766
Tel. (65) 63480378
Fax (65) 63480278
www.garmin.com
https://fly.garmin.com/fly-garmin
Part Number 190-01182-01 Rev. C
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