Date: 201810
Local time of day: 1801-2400
Location: ZZZ.TRACON, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Night
Aircraft: DA42 Twin Star
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Training
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Propeller Control
Component problem: Malfunctioning
Reporter organization: FBO
Reporter function: Instructor; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Flight Instructor
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Requested ATC Assistance / Clarification; Flight Crew Inflight Shutdown
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was in cruise with my student and another instructor in the backseat as well. I noticed we were about 25-30 miles southwest of ZZZ airport and decided I had enough time to simulate an engine [failure]; feather it; and then do a restart. So; I simulated the engine failure by bringing the left throttle to idle; and my student went through all the checklists to identify and verify the engine and do a simulation of restarting the engine; and then deciding to actually feather the engine which is what I wanted him to do. After doing the items for feathering I noticed after about 5 seconds that the propeller was still moving freely and not feathering or shutting off completely. After noticing this; I still had my student keep the controls and go through the checklists for doing an actual restart; and as we were going through these checklist a 'L ALTN FAIL' and 'L OIL PRESS' enunciated on the PFD. Once seeing this; I also tried going through a re-feather checklist to see if I could get the engine to feather since it could help to fly the aircraft smoother. After that failed to work; I told my student I had controls and we gave each other positive control exchange; and asked him to find the alternator failure checklist. After telling me he could not find the checklist I noticed I was only 15 miles southwest at this point from ZZZ and so I asked the instructor in the back to call our head of safety manager to let him know what was happening and then I told my student what I was planning to do and to not touch the controls or rudder; and if I needed assistance I would ask for whatever I needed. I told Approach (we were on VFR flight following) that we were having left engine issues. The Controller asked me where I wanted to land. I told ATC at that time I was about 15 miles south of ZZZ and knowing we can keep straight and level flight that I wanted to continue to the airport. Continued to the airport and eventually asked ATC to switch frequencies to turn on the lights to see the airport/runway better. I eventually landed with no damage to the aircraft or injury to the two other passenger and taxied off of the runway and had to shutdown since it was impossible to taxi with just the right engine. We were off the runway completely when deciding to shut it down. We were towed back by our company that night.




Synopsis: DA42 instructor pilot reported being unable to restore power to the left engine after a simulated engine failure in flight.