Airliner 99
Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Instrument
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation - Speed All Types
Flight Crew Returned To Departure Airport
Aircraft
Student was off on speed and pitch; I thought the student was having issues with pitch had their level reset attitude indicator to see if that began climb again. [It] became obvious after a few minutes their attitude indicator was failing; told Dispatch; looked in MELs; elected to turn back. I took over flying landed; then let the student taxi back to ramp.
C-99 Captain reported an attitude indicator failed midflight resulting in a return to departure airport.