Duchess 76
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 181; Flight Crew Total 1876; Flight Crew Type 140
Troubleshooting
Aircraft Equipment Problem Less Severe
Air Traffic Control Provided Assistance; Flight Crew Inflight Shutdown; Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
My student and [I] were on his 3rd flight in the Duchess. He was receiving instruction from me in pursuit of his Commercial Pilot AMEL Certificate. We departed ZZZ and proceeded to the Palos Verdes/Long Beach Practice Area for our maneuvers. We were at 4500 ft. MSL and were making regular calls on the air to air frequency for the practice area. I was introducing him to Engine Failures in Cruise and the subsequent Air Restart Procedure. We did a few rounds of simulated engine failure procedures where I failed the engine using the throttle. Once he got the hang of the procedure; I failed the Left engine with the mixture and he ran thru the memory items and checklist items and feathered the Left Propeller. We then flew around for a few minutes single engine so I could demonstrate the characteristics of the airplane while single engine.We then began the procedure to air restart the engine. We followed the checklist and ran thru the steps using the Unfeathering Accumulator. The propeller did not come out of the feathered position. We then moved on to the air restart without the unfeathering accumulator and once again the engine did not start. We reattempted this procedure another 4 times and had descended down to 3500ft MSL in the process of gaining airspeed for the air restart. I then made the decision to land as soon as possible at ZZZ1. The decision was 2 fold; that was the closest field to us and the shop that usually works on the plane was based in ZZZ1. I took over control of the plane and asked my student to get the ATIS for ZZZ1. I then called in to tower and advised them of our situation and that we would like to Land on XXR. The controller then cleared us to enter the pattern and advised us that we were number 2 to land and we were cleared. He also asked if I was [requesting priority handling] and I said I was not since I did have positive control of the aircraft. The controller acknowledged and went on to ask for souls and fuel on board.I had to do some s-turns on final to lose altitude and subsequently landed the plane without further incident. I taxied off the runway on my own power and once I was off the runway; I attempted to restart the Left engine. It still would not start after 2 attempts and then finally started but was shuddering quite badly. I quickly taxied off to the non-movement area and shut down while talking to ground control. I called the mechanic and the came and moved the plane to the shop for repair.Overall; I feel that I did what was necessary to avoid any further damage to the aircraft while keeping my student and the general public safe. I was also trying to not cause any undue operational hazards and delays for the airport.
BE-76 Instructor reported failed engine restart attempt in flight.