Narrative:

While taxiing into position for takeoff, got 'heading' flag -- ahrs warning on ehsi's (both). Reset normally. Occurred again during takeoff roll and would not reset. 20 degree error between left and right system. After initial level off, unsuccessfully tried all means of realigning compass system. Having read recent articles on EMI, finally asked flight attendant to check if any passenger were using electronic devices. Almost immediately ahrs 'heading' warning disappeared and ehsi's realigned. Flight attendant reported 1 passenger was using a cellular telephone. In retrospect, I have had numerous instances similar to this one which mysteriously corrected themselves after a period of time.

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Original NASA ASRS Text

Title: GOT A 'HDG' FLAG ON HSI (BOTH) WHEN TAXIING INTO POS, AGAIN DURING TKOF ROLL. THIS HSI ERROR LASTED INTO CRUISE; A PAX HAD BEEN USING A CELLULAR PHONE.

Narrative: WHILE TAXIING INTO POS FOR TKOF, GOT 'HDG' FLAG -- AHRS WARNING ON EHSI'S (BOTH). RESET NORMALLY. OCCURRED AGAIN DURING TKOF ROLL AND WOULD NOT RESET. 20 DEG ERROR BTWN L AND R SYS. AFTER INITIAL LEVEL OFF, UNSUCCESSFULLY TRIED ALL MEANS OF REALIGNING COMPASS SYS. HAVING READ RECENT ARTICLES ON EMI, FINALLY ASKED FLT ATTENDANT TO CHK IF ANY PAX WERE USING ELECTRONIC DEVICES. ALMOST IMMEDIATELY AHRS 'HDG' WARNING DISAPPEARED AND EHSI'S REALIGNED. FLT ATTENDANT RPTED 1 PAX WAS USING A CELLULAR TELEPHONE. IN RETROSPECT, I HAVE HAD NUMEROUS INSTANCES SIMILAR TO THIS ONE WHICH MYSTERIOUSLY CORRECTED THEMSELVES AFTER A PERIOD OF TIME.

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.