HDG TRACK DEV IN A CRJ CL-65 WHEN THE FO; PF; OBSERVES AN EFIS COMPASS MONITOR CAUTION MESSAGE AFTER TKOF FROM DTW; MI.

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DURING TAXI; A PROB WITH ATTITUDE HDG REF 2 SYS (AHRS) AROSE. ELECTRONIC FLT INST SYS (EFIS) COMMON CAUTION MESSAGE AND RED MAGNETIC FLAG ON HSI. HDGS ON FO'S SIDE WERE 45 DEGS OFF. FCOM VOLUME 1 STATES 'HDG INFO FROM THE REMOTE MAGNETIC SENSORS IS SUSCEPTIBLE TO LOCALIZED MAGNETIC FIELDS AND MAGNETIC ANOMALIES. REPOSITIONING THE ACFT OR REMOVAL OF LARGE FERROUS OBJECTS FROM THE IMMEDIATE VICINITY OF THE WINGTIPS MAY ALLOW PROPER HDG INDICATING.' (FCOM VOLUME 1 P 11-7.) ACFT WAS HOLDING JUST E OF DTW K16 RWY 22L. MAINT CONTACTED AND SUGGESTED ACFT BE REPOSITIONED. ACFT MOVED; CAUTION MESSAGES DISAPPEARED; HDG INDICATIONS RETURNED TO NORMAL. WE THEN DEPARTED DTW RWY 22L ON ASSIGNED HDG OF 225 DEGS. AFTER TKOF; PASSING THROUGH 400 FT AGL; WE GOT AN EFIS COMMON CAUTION MESSAGE BUT NO RED FLAG ON HSI. I WAS PF AND FOLLOWED COMMAND STEERING BUT PASSING AROUND 4700 FT MSL DEP BECAME CONCERNED ABOUT OUR HDG. WE INFORMED THEM OF OUR HDG PROB AND THEY STOPPED OUR CLB AT 5000 FT MSL AND ASSIGNED US A SPD OF 180 KIAS WHICH WE COMPLIED WITH. BY THAT TIME; WE HAD IDENTED THE PROB AS BEING AHRS 2 AND QUICKLY SLEWED THE SYS BACK TO THE PROPER HDG. I BELIEVE IT WAS ABOUT 20-30 DEGS OFF. WE WERE TCASII EQUIPPED AND NEVER GOT ANY ALERTS (EITHER TA OR RA). DEP NEVER SAID THAT THERE HAD BEEN A LOSS OF SEPARATION WITH ANY OTHER ACFT. INTERESTINGLY; WE FLEW ACFT FOR REST OF THE DAY (6.0 HRS) AND NEVER GOT ANOTHER HDG PROB. I HAVE BEEN FLYING CRJ CL-65'S AT DTW FOR ABOUT 6 MONTHS AND HAVE EXPERIENCED NUMEROUS EFIS COMMON CAUTION MESSAGES IN THE VICINITY OF RWYS 22L AND 21R. OCCASIONALLY; THEY HAVE OCCURRED AFTER TKOF AS THEY DID THIS DAY.