Functional Testing Page

TRANSPONDER REPAIRS

FLIGHT CONTROL SERVICES FAA CRS#OFHR414L

USE THE ORDER FORM LINK ABOVE TO ORDER SERVICE

Updated DEC 2023

THE FUNCTIONAL TESTING AND EVALUATIONS IN THIS SECTION MAY BE CONDUCTED BY A PRIVATE PILOT IN ACCORDANCE WITH MANUFACTURER’S OPERATING PROCEDURES IF THE TRANSPONDER IS NOT REMOVED.

TO VIEW FAR PART 43 APPENDIX A

THIS SECTION DEALS WITH THE TRANSPONDER ITSELF AND IS WHERE YOU SHOULD START EVEN IF YOU ALREADY SUSPECT AN AIRFRAME RELATED ISSUE OR HAVE MODE C (ALTITUDE REPORTING) PROBLEMS.

INTERACTIVE PARTICIPATION IS IN BLUE BOLD TEXT. COMMENTS OR ADVICE IS IN BLACK TEXT. CLICK ON ANY BUTTONS THAT MAY APPLY AND IGNORE THE REST.

SOME GENERIC TERMS WE USE MAY NOT BE RELEVANT. FOR EXAMPLE TRANSPONDERS WITH ELECTRONIC DISPLAYS DO NOT HAVE REPLY LAMPS AND MAY HAVE BUTTONS RATHER THAN KNOBS.

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WE'LL ASSUME YOU HAVE OBSERVED NO OBVIOUS FAULTS SUCH AS PHYSICAL DAMAGE, MISSING ANTENNA OR OTHER PROBLEMS THAT DEVELOPED AT THE SAME EXACT TIME.

BACKGROUND DETAILS

HAS THERE BEEN ANY MAINTENANCE, UPGRADES OR CHANGES TO YOUR AIRCRAFT THAT CORRESPOND WITH YOUR TRANSPONDER'S FAILURE?

WHEN WAS THE LAST TIME YOUR TRANSPONDER RECEIVED IT'S FAR 91.413 24 MONTH CERTIFICATION?

WAS THIS A INTERMITTENT, PARTIAL OR COMPLETE FAILURE?

HAS THIS TRANSPONDER EVER FAILED BEFORE, BEEN REPAIRED, AND FAILED AGAIN IN THE EXACT SAME WAY?

LET'S ACCESS YOUR ABILITY TO PERFORM MAINTENANCE ON YOUR TRANSPONDER

IF YOU ARE AN A&P MECHANIC OR APPROPRIATELY RATED REPAIRMAN

IF YOU ARE A PRIVATE PILOT OR THE AIRCRAFT'S OWNER.

DO YOU NEED HELP IN SELECTING OR FINDING A LICENSED MECHANIC?

WHAT DO YOU REMEMBER FROM YOUR LAST FLIGHT(s)?
DID THE FAILURE OCCUR DURING AN IFR FLIGHT?

DID YOUR TRANSPONDER REPORT THE WRONG CODE? EXAMPLE: 2200 RATHER THAN 1200.

DID YOUR REPLY LAMP SEEM TO FLASH AS IT NORMALLY DOES?

DID YOU EXPERIENCED INTERMITTENT BEHAVIOR SUCH AS ONE CONTROLLER SEES YOU FINE BUT THE NEXT ONE LOOSES YOU WHEN YOU ARE HANDED OFF?

IF ALTITUDE REPORTING (MODE C) IS INOP OR IN ERROR.

AIRFRAME FUNCTIONAL TESTS AND EVALUATION

INSPECT BELLY MOUNTED ANTENNA

TEST ADJACENT RADIO/BULBS/SYSTEMS FOR OPERATION?

DO THE INTERNAL "PILOT LIGHTS" COME ON WHEN YOU SELECT NIGHT LIGHTING?

THE MOST IMPORTANT ASPECT HERE IS UNDERSTANDING THE BEHAVIOR OF YOUR REPLY LAMP (OR ICON) ESPECIALLY WHEN YOU MANUALLY SELECT THE TEST FUNCTION.

WHEN YOU SELECT TEST, YOU ARE ACTUALLY INJECTING A SIGNAL THAT MIMICS AN ACTUAL ATC INTERROGATION DIRECTLY INTO THE RECEIVER, “TRICKING” IT INTO TRIGGERING A REPLY AFTER PASSING THROUGH THE DECODING, ENCODING AND MOST OR THE REPLY CIRCUITRY. THE REPLY LAMP WILL ILLUMINATE ONLY IF ALL (OR MOST) OF THE CIRCUITS ARE FUNCTIONING.

A SUCCESSFUL TEST DOES NOT MEAN YOU ARE SENDING THE PROPER CODES, ON THE CORRECT FREQUENCY OR HAVE ANTENNA ISSUES. HOWEVER IT GENERALLY INDICATES AN OTHERWISE "HEALTHY" TRANSPONDER.

TRANSPONDER FUNCTIONAL TESTS AND EVALUATION

THE BEHAVIOR OF YOUR REPLY LAMP IS DIRECTLY CONNECTED IN SEVERAL WAYS TO YOUR TRANSPONDER'S HEALTH. IT COULD BE THE KEY IN YOUR DECISION TO SEND THE UNIT IN FOR REPAIR OR TO HAVE THE WIRING AND ANTENNA INSPECTED AND REPAIRED LOCALLY.

IF YOUR TRANSPONDER HAS AN ELECTRONIC DISPLAY

PERFORM THE FOLLOWING IN THE AIRCRAFT. TURN REPLY LAMP DIMMER FULLY CLOCKWISE (IF IT HAS ONE). TURN ON BOTH BATTERY AND AVIONICS MASTERS. DO NOT START ENGINE. BE PREPARED TO OBSERVE AND RECORD WHAT YOU FIND IN STEPS 1 THROUGH 5 ( YOU'LL HAVE TO PULL STEP 6 FROM MEMORY). NOW TURN ON TRANSPONDER IN THE "ALT" MODE AND OBSERVE:

1. REPLY LAMP COMES ON DURING WARM-UP. (MOST UNITS).
2. A HIGH PITCH WHINE MIGHT BE HEARD IF YOU LISTEN VERY CLOSELY.
3. REPLY LAMP GOES OFF IN 15-30 SECONDS. (MOST UNITS).
4. REPLY LAMP WILL COME ON IF UNIT IS PLACED IN TEST MODE.
5. REPLY LAMP WILL COME ON FOR ABOUT 15 SECONDS IF IDENT BUTTON IS PRESSED. (DON'T PRESS IDENT IF YOU SEE ANY REPLY LAMP ACTIVITY).
6. REPLY LAMP DID FLASH DURING FLIGHT.