Narrative:

On oct/wed/03, I picked up my aircraft at 3k6 after being annualed. Part of this annual included the pitot static system/transponder check. This 24 month check was completed and the logs were signed indicating this system was returned to flight status. Upon departing from 3k6, at about 5000 ft, I contacted ZKC and requested flight following to lou at 9500 ft. Some time after leveling off at 9500 ft, ZKC asked what altitude I was climbing to. I advised that I was level at 9500 ft for my final altitude. ZKC advised that my altitude was reading 8900 ft. We tried to recycle the system, but still was reading 600 ft low. When asked to cancel 'altitude squawk,' I found out that the transponder had a switch problem as even in the 'on' position, we were squawking altitude. ZKC canceled my radar service. I then contacted evv approach as I was near their airspace. They assigned a code and when radar contact was established, advised that I was reading 9000 ft instead of the 9500 ft that I reported. I explained what had transpired with ZKC and the evv controller advised that he could provide radar service with the incorrect 'altitude squawk' as long as I advised him prior to any altitude changes. After crossing evv airspace, I was handed off to sdf approach. I incurred the same problems with sdf. My squawk indicated 500-600 ft below reported altitude. As I was descending from 9500 ft to 3500 ft, we checked the squawked versus actual several times and found the error to be consistently 500-600 ft lower than actual. I was handed off to sdf tower. Crossing over the numbers of runway 17L&right at sdf at my assigned altitude of 2500 ft, sdf tower advised that I was reading 2100 ft. As there was traffic below on the approach to runway 17L, tower was concerned and requested confirmation of actual altitude a couple of times. I was then handed off to lou tower. On final for runway 24 at 1100 ft, I asked for an altitude reporting check and was told it read 900 ft (200 ft low). On oct/thu/03, I contacted the shop that performed the annual and was advised that the avionics tech had advised them that the encoder on my aircraft 'may' be intermittent. This bit of very important knowledge was not relayed to me in any manner prior to picking up my aircraft. Corrective actions: I have ordered a new encoder to be installed immediately. Recommended actions: 1) avionics technicians should not sign off the 24 month pilot static/transponder check if there is a question about the reliability of the encoder. 2) the shop doing the annual must communicate all information/concerns, etc, regarding the status of the aircraft and its equipment to the pilot -- prior to returning the aircraft to service.

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Original NASA ASRS Text

Title: MOONEY PLT EXPERIENCED CONTINUED MODE C PROBS IMMEDIATELY AFTER ANNUAL MAINT CHK.

Narrative: ON OCT/WED/03, I PICKED UP MY ACFT AT 3K6 AFTER BEING ANNUALED. PART OF THIS ANNUAL INCLUDED THE PITOT STATIC SYS/XPONDER CHK. THIS 24 MONTH CHK WAS COMPLETED AND THE LOGS WERE SIGNED INDICATING THIS SYS WAS RETURNED TO FLT STATUS. UPON DEPARTING FROM 3K6, AT ABOUT 5000 FT, I CONTACTED ZKC AND REQUESTED FLT FOLLOWING TO LOU AT 9500 FT. SOME TIME AFTER LEVELING OFF AT 9500 FT, ZKC ASKED WHAT ALT I WAS CLBING TO. I ADVISED THAT I WAS LEVEL AT 9500 FT FOR MY FINAL ALT. ZKC ADVISED THAT MY ALT WAS READING 8900 FT. WE TRIED TO RECYCLE THE SYS, BUT STILL WAS READING 600 FT LOW. WHEN ASKED TO CANCEL 'ALT SQUAWK,' I FOUND OUT THAT THE XPONDER HAD A SWITCH PROB AS EVEN IN THE 'ON' POS, WE WERE SQUAWKING ALT. ZKC CANCELED MY RADAR SVC. I THEN CONTACTED EVV APCH AS I WAS NEAR THEIR AIRSPACE. THEY ASSIGNED A CODE AND WHEN RADAR CONTACT WAS ESTABLISHED, ADVISED THAT I WAS READING 9000 FT INSTEAD OF THE 9500 FT THAT I RPTED. I EXPLAINED WHAT HAD TRANSPIRED WITH ZKC AND THE EVV CTLR ADVISED THAT HE COULD PROVIDE RADAR SVC WITH THE INCORRECT 'ALT SQUAWK' AS LONG AS I ADVISED HIM PRIOR TO ANY ALT CHANGES. AFTER XING EVV AIRSPACE, I WAS HANDED OFF TO SDF APCH. I INCURRED THE SAME PROBS WITH SDF. MY SQUAWK INDICATED 500-600 FT BELOW RPTED ALT. AS I WAS DSNDING FROM 9500 FT TO 3500 FT, WE CHKED THE SQUAWKED VERSUS ACTUAL SEVERAL TIMES AND FOUND THE ERROR TO BE CONSISTENTLY 500-600 FT LOWER THAN ACTUAL. I WAS HANDED OFF TO SDF TWR. XING OVER THE NUMBERS OF RWY 17L&R AT SDF AT MY ASSIGNED ALT OF 2500 FT, SDF TWR ADVISED THAT I WAS READING 2100 FT. AS THERE WAS TFC BELOW ON THE APCH TO RWY 17L, TWR WAS CONCERNED AND REQUESTED CONFIRMATION OF ACTUAL ALT A COUPLE OF TIMES. I WAS THEN HANDED OFF TO LOU TWR. ON FINAL FOR RWY 24 AT 1100 FT, I ASKED FOR AN ALT RPTING CHK AND WAS TOLD IT READ 900 FT (200 FT LOW). ON OCT/THU/03, I CONTACTED THE SHOP THAT PERFORMED THE ANNUAL AND WAS ADVISED THAT THE AVIONICS TECH HAD ADVISED THEM THAT THE ENCODER ON MY ACFT 'MAY' BE INTERMITTENT. THIS BIT OF VERY IMPORTANT KNOWLEDGE WAS NOT RELAYED TO ME IN ANY MANNER PRIOR TO PICKING UP MY ACFT. CORRECTIVE ACTIONS: I HAVE ORDERED A NEW ENCODER TO BE INSTALLED IMMEDIATELY. RECOMMENDED ACTIONS: 1) AVIONICS TECHNICIANS SHOULD NOT SIGN OFF THE 24 MONTH PILOT STATIC/XPONDER CHK IF THERE IS A QUESTION ABOUT THE RELIABILITY OF THE ENCODER. 2) THE SHOP DOING THE ANNUAL MUST COMMUNICATE ALL INFO/CONCERNS, ETC, REGARDING THE STATUS OF THE ACFT AND ITS EQUIP TO THE PLT -- PRIOR TO RETURNING THE ACFT TO SVC.

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.