Dash 8-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Landed As Precaution; Flight Crew Returned To Gate; Flight Crew Returned To Departure Airport; General Maintenance Action; General Flight Cancelled / Delayed
Aircraft
During the takeoff at approximately 100 feet we received a message that the yaw damper had disengaged. The message was canceled and the pilot flying attempted to re-engage the yaw damper. The yaw damper was not available and we then received a message that the yaw damper and flight director failed. We continued the climb out to acceleration height. At acceleration height the Pilot Flying lowered the nose from takeoff attitude to 5 degrees for acceleration. We received another message Altitude and Heading Reference System (AHRS) Nav/Data Invalid as well. When the nose was lowered I discovered that my Electronic Altitude Direction Indicator (EADI) was continuing to show a climb attitude and continued to approximately 20-22 degrees nose up. We were still in visual conditions so it was easy to see that we were not at that attitude. I alerted the Pilot Flying that my EADI had failed. At about that same time we noticed that we were still climbing quickly even though the First Officer (FO) EADI showed a 5 degrees nose up. We checked all 3 EADI's and noted that all 3 of the attitude indicators were showing different values. The standby EADI indicated approximately a 10 degree nose up and given our power setting and vertical speed and airspeed indicator we quickly realized that the only EADI that was showing a correct value was the standby instrument. We quickly ran through our options and decided that we would be returning to ZZZ due to primary instrument failure and I [advised ATC] over the radio and stated that we had lost our primary attitude indicators and that we needed to return. We consulted the checklist and found that the message indicated that our instruments were not receiving valid information. We were cleared to 8;000 feet and as we passed 6;000 we realized that we would be quickly entering IMC conditions and that we needed an immediate descent. We then elected to [advise ATC] for priority handling and although we entered IMC for approximately 20 seconds we were able to descend below the clouds rather quickly.We began receiving vectors to land and I began to manage the situation of notifying operations and the passengers while the FO expertly flew the aircraft with the operating instruments. As we were vectored it became obvious that we would not have time to brief the cabin crew properly and I elected to make a PA in order to address the flight attendant and passengers at the same time. Approximately 10-15 minutes after the initial failure we noticed that both EADI instruments began to again work correctly and we were able to engage the yaw damper and flight director. We were vectored for an uneventful landing and notified the Tower that the rescue and firefighter services would not be needed. We returned to the gate and notified operations as well as maintenance. The passengers were deplaned; a maintenance discrepancy was noted in the logbook and we explained to maintenance the problems that occurred.
Dash 8 Captain reported returning to departure airport after experiencing multiple system failures involving the yaw damper; flight directors; and attitude indicators.