Narrative:

Departed 7d2 (within 30 mi of dtw TCA) VFR, and contacted dtw approach to pick up my IFR clearance to flint. Purpose of flight was INS practice work. An appropriately rated and current safety pilot was in the right seat. The aircraft is equipped with a transponder and mode C altitude encoder. Dtw assigned us a transponder code, then advised 'radar contact' and issued my clearance. I read back the clearance and maneuvered the aircraft to assigned heading and altitude. Within the next moment, dtw advised he couldn't read our transponder signal. I recycled the transponder at ATC's request, but this didn't help. In VMC at the time, I asked ATC whether or not I could continue the flight. Dtw instructed me to proceed and handed me off to flint approach. Flint couldn't receive my transponder signal either, until I was within 8 mi of the field. Even then, they could only receive my primary signal, but not mode C. Flint vectored me to the final approach course for the VOR runway 18 approach, and after the low approach I was then cleared IFR for the return to 7d2. Flint lost my transponder signal after about 8 mi. Dtw could received after a while, but only very intermittently. Within 10 mi of 7d2 and in VMC, I cancelled IFR and completed the flight. Pilots need to be aware that xponders are not really testable during preflight operations, and that the only way to know they are not squawking is when so advised by ATC. Sometimes this will occur within the 30 mi mode C veil around a TCA. It is reassuring to know that the ATC people can be patient and helpful in such situations.

Google
 

Original NASA ASRS Text

Title: TRANSPONDER FAILURE DURING PRACTICE INS FLT IN SMA. AFTER DUE NOTIFICATION TO ATC, FLT PROCEEDED ROUTINELY.

Narrative: DEPARTED 7D2 (WITHIN 30 MI OF DTW TCA) VFR, AND CONTACTED DTW APCH TO PICK UP MY IFR CLRNC TO FLINT. PURPOSE OF FLT WAS INS PRACTICE WORK. AN APPROPRIATELY RATED AND CURRENT SAFETY PLT WAS IN THE RIGHT SEAT. THE ACFT IS EQUIPPED WITH A XPONDER AND MODE C ALT ENCODER. DTW ASSIGNED US A XPONDER CODE, THEN ADVISED 'RADAR CONTACT' AND ISSUED MY CLRNC. I READ BACK THE CLRNC AND MANEUVERED THE ACFT TO ASSIGNED HDG AND ALT. WITHIN THE NEXT MOMENT, DTW ADVISED HE COULDN'T READ OUR XPONDER SIGNAL. I RECYCLED THE XPONDER AT ATC'S REQUEST, BUT THIS DIDN'T HELP. IN VMC AT THE TIME, I ASKED ATC WHETHER OR NOT I COULD CONTINUE THE FLT. DTW INSTRUCTED ME TO PROCEED AND HANDED ME OFF TO FLINT APCH. FLINT COULDN'T RECEIVE MY XPONDER SIGNAL EITHER, UNTIL I WAS WITHIN 8 MI OF THE FIELD. EVEN THEN, THEY COULD ONLY RECEIVE MY PRIMARY SIGNAL, BUT NOT MODE C. FLINT VECTORED ME TO THE FINAL APCH COURSE FOR THE VOR RWY 18 APCH, AND AFTER THE LOW APCH I WAS THEN CLRED IFR FOR THE RETURN TO 7D2. FLINT LOST MY XPONDER SIGNAL AFTER ABOUT 8 MI. DTW COULD RECEIVED AFTER A WHILE, BUT ONLY VERY INTERMITTENTLY. WITHIN 10 MI OF 7D2 AND IN VMC, I CANCELLED IFR AND COMPLETED THE FLT. PLTS NEED TO BE AWARE THAT XPONDERS ARE NOT REALLY TESTABLE DURING PREFLT OPS, AND THAT THE ONLY WAY TO KNOW THEY ARE NOT SQUAWKING IS WHEN SO ADVISED BY ATC. SOMETIMES THIS WILL OCCUR WITHIN THE 30 MI MODE C VEIL AROUND A TCA. IT IS REASSURING TO KNOW THAT THE ATC PEOPLE CAN BE PATIENT AND HELPFUL IN SUCH SITUATIONS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.