Narrative:

Approximately 5 mins after takeoff, the altitude indicator (artificial horizon) started to precess. Continued climb on instruments, without difficulty until starting level off procedure at 17000 ft. At that time center advised that I was cleared on course to pne (destination airport). I was on a heading of 010 degrees and started a right turn at the same time I was trying to level off. Without the altitude indicator, I pushed too far forward on the control wheel and the plane started a descent. When the rate of descent was increasing past 1000 FPM, I pulled back on the control wheel to bring the nose up. Instead of slowing the rate of descent, I merely increased the rate of turn, so that we were now in a descending spiral turn. The rate of descent was pegged at 5000 FPM. At that time ATC queried my intentions with a remark like 'we cleared you to pne, but didn't expect you to go by way of kansas city' (or something like that). I chose not to respond until I got the aircraft under control. I decided to look out the aircraft window to get a visual fix on what was happening. Observing ground light in the wind screen moving to my left rapidly, I pushed left rudder and used left aileron to straighten out of the turn, then gradually brought the nose up to pull out of the dive. By that time ATC again queried me and I responded with the report that my gyroscope had failed and requested a 'no-gyroscope' vector back to sus airport. It took another min or so to stabilize the aircraft for descent. I had descended from FL120 to FL130 in about 20-30 seconds. The return to sus was accomplished without further incident.

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Original NASA ASRS Text

Title: RPTR LOSES CTL OF HIS ACFT AND ENTERS A SPIRAL WHEN THE ARTIFICIAL HORIZON FAILS.

Narrative: APPROX 5 MINS AFTER TKOF, THE ALT INDICATOR (ARTIFICIAL HORIZON) STARTED TO PRECESS. CONTINUED CLB ON INSTS, WITHOUT DIFFICULTY UNTIL STARTING LEVEL OFF PROC AT 17000 FT. AT THAT TIME CTR ADVISED THAT I WAS CLRED ON COURSE TO PNE (DEST ARPT). I WAS ON A HDG OF 010 DEGS AND STARTED A R TURN AT THE SAME TIME I WAS TRYING TO LEVEL OFF. WITHOUT THE ALT INDICATOR, I PUSHED TOO FAR FORWARD ON THE CTL WHEEL AND THE PLANE STARTED A DSCNT. WHEN THE RATE OF DSCNT WAS INCREASING PAST 1000 FPM, I PULLED BACK ON THE CTL WHEEL TO BRING THE NOSE UP. INSTEAD OF SLOWING THE RATE OF DSCNT, I MERELY INCREASED THE RATE OF TURN, SO THAT WE WERE NOW IN A DSNDING SPIRAL TURN. THE RATE OF DSCNT WAS PEGGED AT 5000 FPM. AT THAT TIME ATC QUERIED MY INTENTIONS WITH A REMARK LIKE 'WE CLRED YOU TO PNE, BUT DIDN'T EXPECT YOU TO GO BY WAY OF KANSAS CITY' (OR SOMETHING LIKE THAT). I CHOSE NOT TO RESPOND UNTIL I GOT THE ACFT UNDER CTL. I DECIDED TO LOOK OUT THE ACFT WINDOW TO GET A VISUAL FIX ON WHAT WAS HAPPENING. OBSERVING GND LIGHT IN THE WIND SCREEN MOVING TO MY L RAPIDLY, I PUSHED L RUDDER AND USED L AILERON TO STRAIGHTEN OUT OF THE TURN, THEN GRADUALLY BROUGHT THE NOSE UP TO PULL OUT OF THE DIVE. BY THAT TIME ATC AGAIN QUERIED ME AND I RESPONDED WITH THE RPT THAT MY GYROSCOPE HAD FAILED AND REQUESTED A 'NO-GYROSCOPE' VECTOR BACK TO SUS ARPT. IT TOOK ANOTHER MIN OR SO TO STABILIZE THE ACFT FOR DSCNT. I HAD DSNDED FROM FL120 TO FL130 IN ABOUT 20-30 SECONDS. THE RETURN TO SUS WAS ACCOMPLISHED WITHOUT FURTHER INCIDENT.

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.