Narrative:

Dec/xx/91, we were on climb out from hartford/brainard airport (hfd). Our clearance was to maintain a heading of 360 degrees and climb to 3000 ft. We were under hfd departure control at the time. The aircraft, an small transport, was being flown single pilot that day with a total of 5 passenger on board. We were on an instrument flight plan to grand rapids, mi. The WX was ceiling and visibility unlimited. At approximately 1000 ft AGL the autoplt was engaged and progress of the climb was simply monitored by the pilot. At the time of altitude pre-select engagement, we were in a 10 degree pitch-up at a climb rate of approximately 1800 FPM. The altitude pre-select called for level flight at approximately 3080 ft, normal for the system. Due to the relatively high climb rate, however, the aircraft actually ascended to approximately 3150 ft for a few seconds before returning to approximately 3100 ft and holding that altitude. We don't usually trim out to exactly the assigned altitude until we reach our cruise altitude. After level off, an opposite direction aircraft was observed in our 12 O'clock position and about 1 or 2 mi at approximately 4000 ft. No action was made on our part since separation appeared normal. Just before the opposite direction aircraft passed over at about our 12:30 position, we received an altitude alert from hfd departure control that '...we show you at 3300 ft, descending....' a check of both the electric single-pointer pilot's altimeter and the non certified copilot's standard altimeter was made, both indicating approximately 3100 ft. I reported that to departure control and advised that we had the opposite direction traffic in sight prior to it passing overhead. Our first indication of a possible explanation did not occur until after we had reached our cruise altitude of 14000 ft. Center called to advise, '...we have lost your transponder, please recycle....' a check of the in-use #2 transponder/encoder was made. There was no power to the system. The dual-head device was switched back to #1 and power was restored. Center verified that the problem was corrected. Upon landing we were advised to call the tower. Tower supervisor again repeated that the hfd tape appeared to show '...an altitude of 3300 ft with a spike at 3400 ft...and that a possible violation may be filed....'

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Original NASA ASRS Text

Title: CPR SMT ALTDEV PLUS FAULTY MODE C RESULTS IN POSSIBLE VIOLATION BEING FILED BY DEP CTLR.

Narrative: DEC/XX/91, WE WERE ON CLBOUT FROM HARTFORD/BRAINARD ARPT (HFD). OUR CLRNC WAS TO MAINTAIN A HDG OF 360 DEGS AND CLB TO 3000 FT. WE WERE UNDER HFD DEP CTL AT THE TIME. THE ACFT, AN SMT, WAS BEING FLOWN SINGLE PLT THAT DAY WITH A TOTAL OF 5 PAX ON BOARD. WE WERE ON AN INST FLT PLAN TO GRAND RAPIDS, MI. THE WX WAS CEILING AND VISIBILITY UNLIMITED. AT APPROX 1000 FT AGL THE AUTOPLT WAS ENGAGED AND PROGRESS OF THE CLB WAS SIMPLY MONITORED BY THE PLT. AT THE TIME OF ALT PRE-SELECT ENGAGEMENT, WE WERE IN A 10 DEG PITCH-UP AT A CLB RATE OF APPROX 1800 FPM. THE ALT PRE-SELECT CALLED FOR LEVEL FLT AT APPROX 3080 FT, NORMAL FOR THE SYS. DUE TO THE RELATIVELY HIGH CLB RATE, HOWEVER, THE ACFT ACTUALLY ASCENDED TO APPROX 3150 FT FOR A FEW SECONDS BEFORE RETURNING TO APPROX 3100 FT AND HOLDING THAT ALT. WE DON'T USUALLY TRIM OUT TO EXACTLY THE ASSIGNED ALT UNTIL WE REACH OUR CRUISE ALT. AFTER LEVEL OFF, AN OPPOSITE DIRECTION ACFT WAS OBSERVED IN OUR 12 O'CLOCK POS AND ABOUT 1 OR 2 MI AT APPROX 4000 FT. NO ACTION WAS MADE ON OUR PART SINCE SEPARATION APPEARED NORMAL. JUST BEFORE THE OPPOSITE DIRECTION ACFT PASSED OVER AT ABOUT OUR 12:30 POS, WE RECEIVED AN ALT ALERT FROM HFD DEP CTL THAT '...WE SHOW YOU AT 3300 FT, DSNDING....' A CHK OF BOTH THE ELECTRIC SINGLE-POINTER PLT'S ALTIMETER AND THE NON CERTIFIED COPLT'S STANDARD ALTIMETER WAS MADE, BOTH INDICATING APPROX 3100 FT. I RPTED THAT TO DEP CTL AND ADVISED THAT WE HAD THE OPPOSITE DIRECTION TFC IN SIGHT PRIOR TO IT PASSING OVERHEAD. OUR FIRST INDICATION OF A POSSIBLE EXPLANATION DID NOT OCCUR UNTIL AFTER WE HAD REACHED OUR CRUISE ALT OF 14000 FT. CENTER CALLED TO ADVISE, '...WE HAVE LOST YOUR TRANSPONDER, PLEASE RECYCLE....' A CHK OF THE IN-USE #2 TRANSPONDER/ENCODER WAS MADE. THERE WAS NO PWR TO THE SYS. THE DUAL-HEAD DEVICE WAS SWITCHED BACK TO #1 AND PWR WAS RESTORED. CENTER VERIFIED THAT THE PROBLEM WAS CORRECTED. UPON LNDG WE WERE ADVISED TO CALL THE TWR. TWR SUPVR AGAIN REPEATED THAT THE HFD TAPE APPEARED TO SHOW '...AN ALT OF 3300 FT WITH A SPIKE AT 3400 FT...AND THAT A POSSIBLE VIOLATION MAY BE FILED....'

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.