Narrative:

While taxiing, I performed an instrument check and explained its significance to my student/passenger. I was cleared to position and hold (line-up) on runway 34A. After lining up, I checked heading indicator, altitude indicator and turned on transponder, lights and started timer. About a min later, I was cleared for takeoff. Shortly after takeoff, I was given a vector to turn left to 280 degrees. I was now in and out of IMC. Before starting left I took a brief look at my heading indicator and it showed 280 degrees at my 2-3 O'clock position. Observing this, I called tower and questioned their instructions. Tower confirmed left to 280 degrees and said to expedite immediately then handed me off to departure. I reluctantly started a left turn, thinking perhaps they want me to pass back over the airport for separation or timing. As I rolled out on the heading indicator at 280 degrees, departure asked me what I was 'doing up there.' I explained that I was complying with tower's vectors. Departure advised me I was nowhere near 280 degrees and gave my 'no-gyroscope' vectors back to course. A quick check of my compass and heading indicator showed that, in fact, my heading indicator had tumbled some 90 degrees plus or minus, or so. I informed ATC of the situation and reset the heading indicator to the proper heading. The rest of the flight was uneventful, however, there was significant precession of the heading indicator throughout. In the past, I, and other pilots who flew this aircraft, had written up problems with the instrument in question. Before taking the airplane I noticed that the discrepancy sheet was clear and 'assumed' the problems had been corrected. Unfortunately, it was not 'considered' a severe 'write-up' as it was a training aircraft and it acted up intermittently.

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Original NASA ASRS Text

Title: AN SMA TWIN INSTRUCTOR PLT HAD A BADLY PRECESSING HDG GYROSCOPE IN IMC.

Narrative: WHILE TAXIING, I PERFORMED AN INST CHK AND EXPLAINED ITS SIGNIFICANCE TO MY STUDENT/PAX. I WAS CLRED TO POS AND HOLD (LINE-UP) ON RWY 34A. AFTER LINING UP, I CHKED HDG INDICATOR, ALT INDICATOR AND TURNED ON XPONDER, LIGHTS AND STARTED TIMER. ABOUT A MIN LATER, I WAS CLRED FOR TKOF. SHORTLY AFTER TKOF, I WAS GIVEN A VECTOR TO TURN L TO 280 DEGS. I WAS NOW IN AND OUT OF IMC. BEFORE STARTING L I TOOK A BRIEF LOOK AT MY HDG INDICATOR AND IT SHOWED 280 DEGS AT MY 2-3 O'CLOCK POS. OBSERVING THIS, I CALLED TWR AND QUESTIONED THEIR INSTRUCTIONS. TWR CONFIRMED L TO 280 DEGS AND SAID TO EXPEDITE IMMEDIATELY THEN HANDED ME OFF TO DEP. I RELUCTANTLY STARTED A L TURN, THINKING PERHAPS THEY WANT ME TO PASS BACK OVER THE ARPT FOR SEPARATION OR TIMING. AS I ROLLED OUT ON THE HDG INDICATOR AT 280 DEGS, DEP ASKED ME WHAT I WAS 'DOING UP THERE.' I EXPLAINED THAT I WAS COMPLYING WITH TWR'S VECTORS. DEP ADVISED ME I WAS NOWHERE NEAR 280 DEGS AND GAVE MY 'NO-GYROSCOPE' VECTORS BACK TO COURSE. A QUICK CHK OF MY COMPASS AND HDG INDICATOR SHOWED THAT, IN FACT, MY HDG INDICATOR HAD TUMBLED SOME 90 DEGS PLUS OR MINUS, OR SO. I INFORMED ATC OF THE SIT AND RESET THE HDG INDICATOR TO THE PROPER HDG. THE REST OF THE FLT WAS UNEVENTFUL, HOWEVER, THERE WAS SIGNIFICANT PRECESSION OF THE HDG INDICATOR THROUGHOUT. IN THE PAST, I, AND OTHER PLTS WHO FLEW THIS ACFT, HAD WRITTEN UP PROBS WITH THE INST IN QUESTION. BEFORE TAKING THE AIRPLANE I NOTICED THAT THE DISCREPANCY SHEET WAS CLR AND 'ASSUMED' THE PROBS HAD BEEN CORRECTED. UNFORTUNATELY, IT WAS NOT 'CONSIDERED' A SEVERE 'WRITE-UP' AS IT WAS A TRAINING ACFT AND IT ACTED UP INTERMITTENTLY.

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.