Narrative:

Level cruise at FL240, first officer was flying. Autoplt on, in IMC conditions. First indication was captain's FMS and heading began to spin to the left, with the spin of the instrument having a high degree of spin. Next, the autoplt disconnected with the aircraft in a left bank and turning left. We brought the aircraft back to level flight and realized we had no good heading information. Next, ZID called and inquired as to our heading. I responded that we had a problem with our heading information. Next I believe I heard the controller turn another aircraft away from us. We next received an EFIS compass monitor warning message followed by a red heading flag. We ran the abnormal checklist procedure for an EFIS compressor monitor message with a red heading flag. When the checklist procedure had been accomplished, the heading information seemed to be returning to normal. After about another 60 seconds, we felt the heading information we were receiving was good compared to the standby compass. I believe through this whole incident the heading of our aircraft probably varied by 160 degrees to 140 degrees either side of our intended course. The incident lasted anywhere from 3-4 mins. The incident happened in the sector of ZID just east of the controller operating on 134.00 frequency. Other than an ahars failure, I wondered if an electronic device in the cabin could have contributed to this anomaly.

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Original NASA ASRS Text

Title: A CL65 PIC RPT ON POSSIBLE RF INTERFERENCE AND THE ACFT'S SUDDEN TURN WHILE FOLLOWING A SPINNING COMPASS. IN CONTACT WITH ZID, IN.

Narrative: LEVEL CRUISE AT FL240, FO WAS FLYING. AUTOPLT ON, IN IMC CONDITIONS. FIRST INDICATION WAS CAPT'S FMS AND HDG BEGAN TO SPIN TO THE L, WITH THE SPIN OF THE INST HAVING A HIGH DEG OF SPIN. NEXT, THE AUTOPLT DISCONNECTED WITH THE ACFT IN A L BANK AND TURNING L. WE BROUGHT THE ACFT BACK TO LEVEL FLT AND REALIZED WE HAD NO GOOD HDG INFO. NEXT, ZID CALLED AND INQUIRED AS TO OUR HDG. I RESPONDED THAT WE HAD A PROB WITH OUR HDG INFO. NEXT I BELIEVE I HEARD THE CTLR TURN ANOTHER ACFT AWAY FROM US. WE NEXT RECEIVED AN EFIS COMPASS MONITOR WARNING MESSAGE FOLLOWED BY A RED HDG FLAG. WE RAN THE ABNORMAL CHKLIST PROC FOR AN EFIS COMPRESSOR MONITOR MESSAGE WITH A RED HDG FLAG. WHEN THE CHKLIST PROC HAD BEEN ACCOMPLISHED, THE HDG INFO SEEMED TO BE RETURNING TO NORMAL. AFTER ABOUT ANOTHER 60 SECONDS, WE FELT THE HDG INFO WE WERE RECEIVING WAS GOOD COMPARED TO THE STANDBY COMPASS. I BELIEVE THROUGH THIS WHOLE INCIDENT THE HDG OF OUR ACFT PROBABLY VARIED BY 160 DEGS TO 140 DEGS EITHER SIDE OF OUR INTENDED COURSE. THE INCIDENT LASTED ANYWHERE FROM 3-4 MINS. THE INCIDENT HAPPENED IN THE SECTOR OF ZID JUST E OF THE CTLR OPERATING ON 134.00 FREQ. OTHER THAN AN AHARS FAILURE, I WONDERED IF AN ELECTRONIC DEVICE IN THE CABIN COULD HAVE CONTRIBUTED TO THIS ANOMALY.

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.