Narrative:

Climbing through 3;500 feet; I noticed the captain's eadi (electronic attitude director indicator) was a few degrees low. I began to level the aircraft off and asked the first officer to query ATC for a descent to 3;000 where we knew VFR conditions existed. In the descent; we received an eadi pitch/roll mismatch message on the advisory display panel. Initially; it appeared that the captain's eadi was the culprit; however as I was discussing a transfer of controls to the first officer; we realized both eadis were displaying erroneous indications. In level flight; the captain's eadi indicated 20 degrees pitch up and 20 degrees left bank; while the first officer's eadi indicated level pitch attitude but 10 degrees left bank. I asked for the emergency checklist; and continued flying the aircraft utilizing the standby attitude indicator. During the checklist; I took over control of the radios. [ATC was advised]. I asked the first officer to brief the passengers and the flight attendant; who told us the aircraft was ready for landing. At 3;000 feet we had VFR conditions; however we asked for a vector to runway xxc; where we landed safely approximately 10 minutes after departure; approximately 800 lbs over maximum landing weight. We taxied to the gate and entered two discrepancies into the aircraft logbook. I was told soon after that the #1 attitude heading reference system was the problem; and it was replaced after our flight. I am unsure if we could have prevented this problem; however I am satisfied in the safe result.

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Original NASA ASRS Text

Title: Dash 8-200 Captain reported returning to the departure airport after noticing both electronic attitude director indicator (EADI) were giving erroneous readings. On the ground; AHRS Number 1 was replaced.

Narrative: Climbing through 3;500 feet; I noticed the Captain's EADI (Electronic Attitude Director Indicator) was a few degrees low. I began to level the aircraft off and asked the FO to query ATC for a descent to 3;000 where we knew VFR conditions existed. In the descent; we received an EADI PITCH/ROLL MISMATCH message on the advisory display panel. Initially; it appeared that the Captain's EADI was the culprit; however as I was discussing a transfer of controls to the First Officer; we realized both EADIs were displaying erroneous indications. In level flight; the Captain's EADI indicated 20 degrees pitch up and 20 degrees left bank; while the FO's EADI indicated level pitch attitude but 10 degrees left bank. I asked for the emergency checklist; and continued flying the aircraft utilizing the standby attitude indicator. During the checklist; I took over control of the radios. [ATC was advised]. I asked the first officer to brief the passengers and the flight attendant; who told us the aircraft was ready for landing. At 3;000 feet we had VFR conditions; however we asked for a vector to runway XXC; where we landed safely approximately 10 minutes after departure; approximately 800 lbs over maximum landing weight. We taxied to the gate and entered two discrepancies into the aircraft logbook. I was told soon after that the #1 Attitude Heading Reference System was the problem; and it was replaced after our flight. I am unsure if we could have prevented this problem; however I am satisfied in the safe result.

Data retrieved from NASA's ASRS site 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.