Avionics Troubleshooting

This avionics troubleshooting guide comes from R.C. Avionics. It is a great compilation of tips and guidance in troubleshooting avionics problems. R.C. Avionics suggests keeping a copy of this guide in the airplane.

General Troubleshooting
• Check the aircraft breaker or fuses. Reset only once.
• Is the electrical system properly charging?
• Could water have leaked onto the avionics?
• Could a connector be loose or wire broken from recent maintenance?
• Do you hear alternator or mag noise?
• Are any antennas missing, corroded, dirty, broken, oil coated, or delaminated?
• Is the problem intermittent?
• Could heat, cold, altitude or time be a factor?

Loran
• Has the correct triad been selected?
• Is manual triad mode selected?
• Verify the correct waypoint.
• Is there a NORAM of any outages?
• Are the signal and SNR levels adequate?
• Are you in a fringe coverage area?
• Is precipitation static a factor?
• Does it have the latest hardware/software updates?
• Check present position or nearest airport.
• Are there any warning or error messages?
• Is interference also affecting the ADF?
• Are you near a thunderstorm?
• Is the NAV selected to an ILS frequency locking out course deviation?

Transponder
• Is ATC receiving both Mode-A (squawk code) and Mode-C (altitude)?
• Has the problem occurred with more than one ATC facility?
• Is Mode-C inoperative or just reporting the wrong altitude?
• Does the reply light illuminate in radar coverage?
• Is the reply light dimmer turned down?
• Is it in the correct mode (stand-by/on/altitude)?
• Does it recycle (power off, then on, then wait 30 seconds)?
• Does turning off the DME resolve the problem?

Com/Audio Panel/Intercom
• Is the correct frequency active (not stand-by)?
• Are the audio switches set correctly?
• Is the auto mode being used?
• Is the same radio selected for transmit and receive?
• Is the volume turned down?
• Is a mic key stuck?
• Are both the headphone and speaker working?
• Does it both receive and transmit?
• Do you hear your voice in the headphone during transmit (sidetone)?
• Did ATC say they heard carrier only without voice?
• Is there background noise when in test mode (squelch off)?
• Try a different headset or microphone.
• Try emergency or isolation modes.
• Are the plugs or jacks dirty, corroded or loose?
• Do all crew and passenger headset locations have the same problem?
• Does another com act the same way?
• Is the oxygen mic switch in the proper position?

Autopilot
• Review operating procedures.
• Does it pass self-test on the ground?
• Does the auto trim work?
• Does the manual electric trim work?
• Does it engage?
• Can you overpower it on the ground?
• Do the controls lock when engaged?
• Could the cables be loose from maintenance?
• Is the aircraft out of trim?
• Is the horizon gyro precessing?
• Is the gyro vacuum within limits?
• Does it hold the wings level?
• Does it hold heading?
• Does it lose altitude in a turn?
• Does it porpoise?
• Does it respond in NAV mode?
• How does it respond on an ILS?

Radar
• Does it paint rain and ground clutter?
• Is the gain turned down?
• Is the brightness turned down?
• Does it test?
• Does it display wheel spokes?
• Does the tilt work?
• Are the images smeared?
• Does it lose targets within 40 miles?
• Is the radome damaged or delaminating or leaking?
• Is stabilization working?

DME
• Does it receive an ident code? (Listen for 60 seconds.)
• Is the remote channeling switch set?
• Is the display dimmed?
• Does the GS and TTS function? (Flying directly to/from but not over station.)
• Is the problem present on other frequencies?
• Does it test?
• Is there a NOTAM of any outages?

ADF
• Is it on the correct frequency?
• Is the unit in ADF mode?
• Does it point to the station?
• Does the needle move in test?
• Does the unit receive in ANT mode?
• Does the unit receive in ADF mode?
• Do all three frequency bands work – (200-399, 400-799, 800-1699)?
• Do you hear alternator or mag noise?
• Is the reception better on the ground with the engine(s) off?
• Are other radios interfering with the ADF?
• Are there thunderstorms in the area?
• Is there a NOTAM of any outages?

Lightning Detection
• Does it pass self test?
• Does it display aircraft electrical noise?
• Is heading orientation functioning?
• In a turn, are the dots all in the same relative direction?
• Is the brightness turned down?

GPS
• Verify the correct waypoint.
• Check present position or nearest airport.
• Are at least three satellites being tracked (VFR) or four satellites (IFR)?
• Is the satellite geometry poor?
• Are the satellite signal levels adequate?
• Has the unit been inactive for a few months?
• Is the hold or OBS mode selected?
• Is the NAV selected to an ILS frequency locking out course indication?
• Is there a NOTAM of any outages?
• Are there any warning or error messages?
• Does it have the latest hardware/software updates?

VOR/ILS
• Is the correct frequency active (not stand-by)?
• Does it receive the ident code?
• Do the needles or flags move at all?
• Can you select a reciprocal OBS course?
• Does the To/From indicator work?
• How many degrees off is the VOR?
• Does the NAV test (self or VOT)?
• Does it have 20° course width peg to peg?
• Do both NAV radios have the same problem?
• Does the localizer work but not the VOR?
• Are you close or far from the station?
• Does a change in engine rpm have an effect?
• Is the RNAV or PAR mode active?
• Is the Loran/GPS switched to the indicator?
• Is there a NOTAM of any outages?
• Is the problem present on different frequencies?
• Does VOR station position relative to the aircraft have an effect?

Marker Beacon
• Do the lamps illuminate over markers?
• Do lamps test?
• Are the lamps dimmed?
• Is problem resolved when high sensitivity is selected?
• Is the audio turned down or not selected?
• Are lights seen but tones not heard?
• Are the correct tones heard?