Narrative:

I was given clearance 'after takeoff left turn to 260 degrees. After completing turn to 260 degree heading on my HSI, the controller called and told me to make a sharp left and asked for my heading. He said I was flying 30 degrees plus off. He gave me an additional vector which I turned to which was also 30 degree plus off. I compared the 2 HSI, they agreed to within 10 degrees, but the overhead compass was in agreement with the 30 degree off mentioned by the controller. I then switched to using the compass for navigation and canceled my IFR flight plan since it was VMC and also looked at the ground for visual confirmation since I was familiar with the area. After checking various system I determined that the a and P who had worked on the plane the previous night had turned off the slave mode on both HSI's. When doing the preflight check since both HSI's roughly agreed with each other and were in the approximately correct direction I did not look at the slave switch. While taxiing across airport for takeoff with many turns and with almost 180 degrees required after takeoff, the HSI's must have drifted by 30 degrees or more. In future slave switches will be part of my preflight and differences between HSI's and the overhead compass will be more closely monitored.

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Original NASA ASRS Text

Title: DEV FROM CLRNC - PLT DID AN INCOMPLETE PREFLT AND DID NOT CHK HIS HSI SO HIS HDG WAS 30 DEGS OFF.

Narrative: I WAS GIVEN CLRNC 'AFTER TKOF L TURN TO 260 DEGS. AFTER COMPLETING TURN TO 260 DEG HDG ON MY HSI, THE CTLR CALLED AND TOLD ME TO MAKE A SHARP L AND ASKED FOR MY HDG. HE SAID I WAS FLYING 30 DEGS PLUS OFF. HE GAVE ME AN ADDITIONAL VECTOR WHICH I TURNED TO WHICH WAS ALSO 30 DEG PLUS OFF. I COMPARED THE 2 HSI, THEY AGREED TO WITHIN 10 DEGS, BUT THE OVERHEAD COMPASS WAS IN AGREEMENT WITH THE 30 DEG OFF MENTIONED BY THE CTLR. I THEN SWITCHED TO USING THE COMPASS FOR NAV AND CANCELED MY IFR FLT PLAN SINCE IT WAS VMC AND ALSO LOOKED AT THE GND FOR VISUAL CONFIRMATION SINCE I WAS FAMILIAR WITH THE AREA. AFTER CHKING VARIOUS SYS I DETERMINED THAT THE A AND P WHO HAD WORKED ON THE PLANE THE PREVIOUS NIGHT HAD TURNED OFF THE SLAVE MODE ON BOTH HSI'S. WHEN DOING THE PREFLT CHK SINCE BOTH HSI'S ROUGHLY AGREED WITH EACH OTHER AND WERE IN THE APPROX CORRECT DIRECTION I DID NOT LOOK AT THE SLAVE SWITCH. WHILE TAXIING ACROSS ARPT FOR TKOF WITH MANY TURNS AND WITH ALMOST 180 DEGS REQUIRED AFTER TKOF, THE HSI'S MUST HAVE DRIFTED BY 30 DEGS OR MORE. IN FUTURE SLAVE SWITCHES WILL BE PART OF MY PREFLT AND DIFFERENCES BTWN HSI'S AND THE OVERHEAD COMPASS WILL BE MORE CLOSELY MONITORED.

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.