Narrative:

While holding short we experienced heading issues; noted by heading flags and amber EFIS miscompare cas message from the ahrs system. We each attempted a reset of our heading system by selecting dg mode on our heading and then switching back to the normal compass sensing. We again received the same heading warnings and reverted back and remained in dg mode as we were cleared for a immediate takeoff from tower. We were given several turns from departure and noticed our headings had drifted apart and decided to double check the standby heading indicator. This was rather difficult in climbing; accelerating flight. We notified departure that we were having issues with our heading and they informed us that they 'would keep an eye on us.' we were given a frequency change to center and the new controller gave us a 'direct to' earnd intersection. At this time we selected normal compass (slaved) mode and selected direct to on the FMS. At this point both headings spun in opposite directions and a FMS message informed us that it was in dr mode. The FMS also gave a message that its' position was unknown for greater than 5 minutes. It took another 5 minutes before we were able to correct these problems and numerous heading changes from ATC.

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Original NASA ASRS Text

Title: CL300 Flight Crew reports AHRS Comp CAS message while holding short and switches to DG for takeoff. After takeoff headings begin to drift apart and ATC is advised. A direct clearance is issued by ATC and entered in the FMC and the AHRS switched back to compass. Both compass cards spin in opposite directions and the FMS goes into DR mode with a position unknown message. After five minutes the FMS returns to normal and after another five minutes the AHRS returns to normal.

Narrative: While holding short we experienced heading issues; noted by HDG flags and amber EFIS MISCOMPARE CAS message from the AHRS system. We each attempted a reset of our heading system by selecting DG mode on our heading and then switching back to the normal compass sensing. We again received the same heading warnings and reverted back and remained in DG mode as we were cleared for a immediate takeoff from tower. We were given several turns from departure and noticed our headings had drifted apart and decided to double check the standby heading indicator. This was rather difficult in climbing; accelerating flight. We notified Departure that we were having issues with our heading and they informed us that they 'would keep an eye on us.' We were given a frequency change to Center and the new controller gave us a 'direct to' EARND intersection. At this time we selected normal compass (slaved) mode and selected direct to on the FMS. At this point both headings spun in opposite directions and a FMS message informed us that it was in DR MODE. The FMS also gave a message that its' position was unknown for greater than 5 minutes. It took another 5 minutes before we were able to correct these problems and numerous heading changes from ATC.

Data retrieved from NASA's ASRS site as of April 2012 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.