Garmin GPS 155 Manual

The Garmin GPS 155 is a panel-mounted TSO-C129a certified GPS receiver and navigation system designed for general aviation. It provides VFR and IFR enroute, terminal, and non-precision approach capability. Below are key sections for safety, features, installation, setup, operation, and troubleshooting.

Features at a Glance

Key components: 3.5-inch monochrome LCD display, Front panel controls, Antenna connector, Serial data ports, Audio output, Power connector.

Feature	Description
Display	3.5-inch high-contrast LCD with backlight
Navigation Modes	Enroute, Terminal, Oceanic, Non-Precision Approach
Database	Jeppesen NavData (28-day cycle)
Antenna connector	For external GPS antenna (typically TNC)
Serial ports	For connection to other avionics (HSI, CDI, autopilot)
Audio output	For aural annunciations and alerts
Power connector	For aircraft 14/28V DC power
PWR/VOL knob	Combined power switch and volume control
Cursor/ENT knob	For menu navigation and data entry
Direct-to Key	Direct navigation to a waypoint

Installation

Unpack and inspect contents. Installation must be performed by a certified avionics technician.

1. Mount unit: Secure in standard 3 ATI panel cutout.
2. Connect antenna: Route coaxial cable to external GPS antenna location.
3. Connect power: Wire to aircraft bus per wiring diagram (typically pins 1 & 2).
4. Connect avionics: Wire serial data ports to HSI, CDI, or autopilot as required.
5. Connect audio: Wire audio output to aircraft intercom or audio panel.

WARNING! Installation and wiring must comply with FAA regulations and aircraft maintenance manuals. Ensure power is OFF during installation.

First-Time Setup

Power on unit; follow initialization prompts.

1. Initialization: Unit will perform self-test and acquire satellite signals (may take several minutes).
2. Set position: If required, enter current aircraft position manually or allow GPS to acquire.
3. Configure interfaces: In SETUP menu, configure serial port data formats (NMEA 0183, ARINC 429) to match connected equipment.
4. Set preferences: Configure units (nm/km), north reference (True/Mag), time format, etc.

CAUTION! Do not use for primary navigation until satellite acquisition is complete and position is verified.

Specifications

• Display: 3.5-inch monochrome LCD, 240 x 128 pixels.
• Channels: 8 parallel channel receiver.
• Update Rate: 1 second.
• Accuracy: <15 meters RMS, 100 meters non-precision approach.
• Velocity Accuracy: 0.1 knot RMS.
• Database: Jeppesen NavData, includes airports, VORs, NDBs, intersections, approaches, SIDs/STARs.
• Interfaces: 2 RS-232 serial ports, ARINC 429 (optional), audio output.
• Power Requirements: 11-33V DC, 1.5A max.
• Operating Temp: -15°C to +55°C.
• TSO: C129a Class A1.

Controls and Settings

Access functions via front panel knobs and soft keys. Primary controls: PWR/VOL knob, Cursor/ENT knob, Direct-to key, CLR key, MENU key.

Primary Pages: NAV (compass rose & data), WPT (waypoint information), AUX (auxiliary functions), NRST (nearest airports).

Setup Menu: Configure system (units, alarms, interfaces), calibrate external magnetometer (if connected), view system status (satellites, signal strength). Database: View and verify current database effective dates. Alerts: Set minimum safe altitude (MSA), airspace alerts.

Connecting Devices

GPS Antenna: TNC connector on rear. Serial Data: Port 1 & 2 for HSI/CDI/Autopilot. Audio: To audio panel or intercom.

1. Ensure aircraft power is OFF.
2. Use shielded cables for all data connections.
3. Configure baud rate and protocol in SETUP menu to match connected device.
4. Verify data transfer on appropriate navigation pages.

Tip: Refer to the Interface Specification document for detailed pinouts and data formats.

Database & Updates

Uses Jeppesen NavData card (28-day cycle).

1. Power off unit.
2. Insert new database card into front slot.
3. Power on. Unit will automatically recognize and load new data.
4. Verify new effective dates on AUX > Database page.
5. Remove and securely store old data card.

WARNING! Navigation using expired database is prohibited for IFR operations. Always verify database is current.

Flight Planning

Create and activate flight plans.

1. From AUX page, select FLIGHT PLAN.
2. Create new plan: Enter departure, destination, and optional enroute waypoints.
3. Activate plan: Select plan and press ACTIVATE.
4. Modify in flight: Insert or delete waypoints as needed.
5. Direct-to: Press D-> key and enter waypoint identifier for immediate navigation.
6. Nearest airports: Press NRST key for list of closest fields with runway and frequency data.

Note: Flight plans are stored in volatile memory and will be lost if power is removed.

Care & Maintenance

Power off before cleaning. Use a soft, dry cloth for display and bezel. Do not use liquids or aerosols.

CAUTION! Ensure air vents on side and rear are not obstructed. Have unit inspected and tested periodically by qualified avionics personnel.

Regulatory Information

TSO-C129a Class A1 certified for IFR enroute, terminal, and non-precision approach operations when installed per applicable guidelines. This device complies with part 15 of the FCC Rules. Copyright © Garmin Ltd. or its subsidiaries. For technical support, contact Garmin Aviation Support or visit www.garmin.com.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No Power	Power connection, circuit breaker	Check aircraft power; verify circuit breaker; check wiring at connector.
"Acquiring Satellites" message persists	Antenna, obstruction, initialization	Verify antenna connection; ensure clear view of sky; allow more time for first acquisition.
Inaccurate position	Poor satellite geometry, RAIM	Check satellite page for adequate coverage and geometry; RAIM prediction available on AUX page.
No data to HSI/Autopilot	Serial configuration, wiring	Verify serial port settings match connected device; check wiring continuity.
Database not recognized	Card insertion, card damage	Ensure card is fully inserted; try a different database card.

Reset: Power cycle unit. For persistent issues, perform Master Reset from AUX page (erases all user settings and flight plans).

Service: Contact Garmin Aviation Product Support. Do not attempt internal repairs.