Narrative:

Our aircraft was told to descend and maintain 11000 ft MSL. We descended out of approximately 16000 ft. Approaching 11000 ft MSL and turning to join the sinca arrival into hartsfield, the autoplt was on. We received an ahrs master caution. At this time the autoplt disengaged and the aircraft descended below 11000 ft to approximately 10740 ft. Both sides (pilot/controller) ahrs were in disagreement and after running the checklist items, we continued to have problems. Needless to say, we had to hand fly the rest of the flight as we were not able to continue use of autoplt as ahrs problem remained. We did push/use the automatic erect push button and that helped temporarily, but eventually the ahrs master caution would come back. On the ground, maintenance was called out to the aircraft to troubleshoot/fix the problem. Callback conversation with reporter revealed the following information: reporter stated maintenance looked at the EFIS system display and mentioned something about adjustment of a component. The reporter said maintenance has not advised the crew of the actual fix.

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Original NASA ASRS Text

Title: AN ATR 72 ON APCH AT 11000 FT HAD ATTITUDE REF DISAGREEMENT BTWN #1 AND #2 SYS WITH AUTOPLT DISCONNECT AND MASTER CAUTION WARNING.

Narrative: OUR ACFT WAS TOLD TO DSND AND MAINTAIN 11000 FT MSL. WE DSNDED OUT OF APPROX 16000 FT. APCHING 11000 FT MSL AND TURNING TO JOIN THE SINCA ARR INTO HARTSFIELD, THE AUTOPLT WAS ON. WE RECEIVED AN AHRS MASTER CAUTION. AT THIS TIME THE AUTOPLT DISENGAGED AND THE ACFT DSNDED BELOW 11000 FT TO APPROX 10740 FT. BOTH SIDES (PLT/CTLR) AHRS WERE IN DISAGREEMENT AND AFTER RUNNING THE CHKLIST ITEMS, WE CONTINUED TO HAVE PROBS. NEEDLESS TO SAY, WE HAD TO HAND FLY THE REST OF THE FLT AS WE WERE NOT ABLE TO CONTINUE USE OF AUTOPLT AS AHRS PROB REMAINED. WE DID PUSH/USE THE AUTO ERECT PUSH BUTTON AND THAT HELPED TEMPORARILY, BUT EVENTUALLY THE AHRS MASTER CAUTION WOULD COME BACK. ON THE GND, MAINT WAS CALLED OUT TO THE ACFT TO TROUBLESHOOT/FIX THE PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED MAINT LOOKED AT THE EFIS SYS DISPLAY AND MENTIONED SOMETHING ABOUT ADJUSTMENT OF A COMPONENT. THE RPTR SAID MAINT HAS NOT ADVISED THE CREW OF THE ACTUAL FIX.

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.