Narrative:

En route (approximately 10 mins after departure) while climbing to assigned altitude, I noticed my magnetic compass and heading indicator on my HSI were not in agreement. Immediately after I got a call from ATC that I was tracking off course. I informed ATC of my apparent problem and he gave me a no-gyro turn back on course. After leveling I noticed my artificial horizon (vacuum) and my backup (electric) were in disagreement. I reset the electric gyro to read the same as my vacuum attitude indicator. Apparently the vacuum attitude indicator was giving false information indicating level flight when actually I was in a turn. Adding to the confusion was the fact that my heading indicator was frozen at a heading of 355 degrees. The controller at ZTL had to give me several 'no gyro turns' to keep me on the arwy, until I could sort out what was going on with my flight instruments. I had several instruments, at least 2, giving me false information. The aircraft had not been flown but approximately 20 hours in the last 6 months, and most or all of that was in VMC. The VOR's had been tested a few days before the trip and the pitot static system tested the month before when a blind encoder was installed. The aft is at the avionics shop at the time of this report awaiting necessary repairs, but no testing has been done yet. I suspect some problem with the vacuum system because I was not getting correct information from the heading indicator and altitude indicator. Also in moderate chop, the turn coordinator was bouncing around, so it was not useful in giving me bank information. The only instrument that was working reliably was the magnetic compass, but on a northerly heading. The magnetic compass is not useful in determining bank. I had reset the backup altitude indicator earlier in flight to read the same as my main altitude indicator, so therefore it was useless also. The result: I wandered around the arwy for 20 mins west/O reliable bank information relying on the controller at ZTL until I determined which instrument was out. I discovered the airplane was in level bank when the attitude indicator was showing a 5 degree turn to the left. Also, center reported altitude readout of 8700' when I was level at 9000' with correct setting. That, also, is being tested. There was no dangerous, hazardous condition or situation, or traffic conflict as a result of this flight that I was or am aware of. ATC was very helpful and professional. I'm filing this report because of the possibility of a traffic conflict that I'm not aware of, and for your benefit in investigating irregularities.

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Original NASA ASRS Text

Title: GA SMT DEVELOPED INSTRUMENT PROBLEMS ON NIGHT CROSS-COUNTRY IMC.

Narrative: ENRTE (APPROX 10 MINS AFTER DEP) WHILE CLBING TO ASSIGNED ALT, I NOTICED MY MAGNETIC COMPASS AND HEADING INDICATOR ON MY HSI WERE NOT IN AGREEMENT. IMMEDIATELY AFTER I GOT A CALL FROM ATC THAT I WAS TRACKING OFF COURSE. I INFORMED ATC OF MY APPARENT PROB AND HE GAVE ME A NO-GYRO TURN BACK ON COURSE. AFTER LEVELING I NOTICED MY ARTIFICIAL HORIZON (VACUUM) AND MY BACKUP (ELECTRIC) WERE IN DISAGREEMENT. I RESET THE ELECTRIC GYRO TO READ THE SAME AS MY VACUUM ATTITUDE INDICATOR. APPARENTLY THE VACUUM ATTITUDE INDICATOR WAS GIVING FALSE INFO INDICATING LEVEL FLT WHEN ACTUALLY I WAS IN A TURN. ADDING TO THE CONFUSION WAS THE FACT THAT MY HDG INDICATOR WAS FROZEN AT A HDG OF 355 DEGS. THE CTLR AT ZTL HAD TO GIVE ME SEVERAL 'NO GYRO TURNS' TO KEEP ME ON THE ARWY, UNTIL I COULD SORT OUT WHAT WAS GOING ON WITH MY FLT INSTRUMENTS. I HAD SEVERAL INSTRUMENTS, AT LEAST 2, GIVING ME FALSE INFO. THE ACFT HAD NOT BEEN FLOWN BUT APPROX 20 HRS IN THE LAST 6 MONTHS, AND MOST OR ALL OF THAT WAS IN VMC. THE VOR'S HAD BEEN TESTED A FEW DAYS BEFORE THE TRIP AND THE PITOT STATIC SYS TESTED THE MONTH BEFORE WHEN A BLIND ENCODER WAS INSTALLED. THE AFT IS AT THE AVIONICS SHOP AT THE TIME OF THIS RPT AWAITING NECESSARY REPAIRS, BUT NO TESTING HAS BEEN DONE YET. I SUSPECT SOME PROB WITH THE VACUUM SYS BECAUSE I WAS NOT GETTING CORRECT INFO FROM THE HDG INDICATOR AND ALT INDICATOR. ALSO IN MODERATE CHOP, THE TURN COORDINATOR WAS BOUNCING AROUND, SO IT WAS NOT USEFUL IN GIVING ME BANK INFO. THE ONLY INSTRUMENT THAT WAS WORKING RELIABLY WAS THE MAGNETIC COMPASS, BUT ON A NORTHERLY HDG. THE MAGNETIC COMPASS IS NOT USEFUL IN DETERMINING BANK. I HAD RESET THE BACKUP ALT INDICATOR EARLIER IN FLT TO READ THE SAME AS MY MAIN ALT INDICATOR, SO THEREFORE IT WAS USELESS ALSO. THE RESULT: I WANDERED AROUND THE ARWY FOR 20 MINS W/O RELIABLE BANK INFO RELYING ON THE CTLR AT ZTL UNTIL I DETERMINED WHICH INSTRUMENT WAS OUT. I DISCOVERED THE AIRPLANE WAS IN LEVEL BANK WHEN THE ATTITUDE INDICATOR WAS SHOWING A 5 DEG TURN TO THE LEFT. ALSO, CENTER RPTED ALT READOUT OF 8700' WHEN I WAS LEVEL AT 9000' WITH CORRECT SETTING. THAT, ALSO, IS BEING TESTED. THERE WAS NO DANGEROUS, HAZARDOUS CONDITION OR SITUATION, OR TFC CONFLICT AS A RESULT OF THIS FLT THAT I WAS OR AM AWARE OF. ATC WAS VERY HELPFUL AND PROFESSIONAL. I'M FILING THIS RPT BECAUSE OF THE POSSIBILITY OF A TFC CONFLICT THAT I'M NOT AWARE OF, AND FOR YOUR BENEFIT IN INVESTIGATING IRREGULARITIES.

Data retrieved from NASA's ASRS site as of August 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.