Duchess 76
Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Commercial
Workload; Troubleshooting; Situational Awareness; Time Pressure; Training / Qualification
Aircraft Equipment Problem Critical; Inflight Event / Encounter Other / Unknown
Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition; Flight Crew Inflight Shutdown; General Maintenance Action
Aircraft
I was conducting a training flight with my student practicing engine failure during flight. I intentionally shut down the right engine and attempted an air start with the unfeathering accumulator. The engine would not start and the propeller was still feathered. [Without success]; we tried an air start using the starter. The engine heavily vibrated for 20 seconds so we shut down and followed the procedure again; but the engine heavily vibrated again for another 30 seconds. We tried to adjust the power; but we had strong vibrations from the engine. After three unsuccessful attempts to air start the engine per emergency checklist; I decided to shut down and secure the engine; and come back to and land. I [requested priority handling]; joined left traffic and performed a one engine inoperative landing. We landed safely and were towed back to the ramp and parked the plane.
Multiengine Flight Instructor reported inability to restart engine inflight during training.