Date: 202103
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: PA-44 Seminole/Turbo Seminole
Operator: FBO
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Propeller
Component problem: Failed
Reporter organization: Personal
Reporter function: Trainee
Reporter qualification: Flight Crew Private; Flight Crew Instrument; Flight Crew Student
Human factors: Troubleshooting
Second reporter function: Instructor
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Human Factors; Aircraft
Primary problem: Ambiguous

Narrative: At around XA:00L time; my instructor and I were practicing engine out procedures per [the training] course. When we tried to complete the checklist for an engine air restart; the propeller failed to unfeather. Upon retrying the checklist; the engine would still not start. We then tried to troubleshoot the engine and nothing would make the propeller unfeather. My instructor made the decision to proceed back [to] the airport and request priority handling. We requested priority with ZZZ Tower requesting to land immediately. My instructor then took over controls; flew us back and landed safely. While he taxied us back; I completed the after landing checklist and we shut down on ZZZ's North ramp.


Second narrative: On a training flight in a PA-44-180 with (L)/IO-360-B1G6 engines installed I (MEI) was the PIC the student was acting PIC. At 6;000 ft MSL in the practice area north of ZZZ; I intentionally failed the left engine by bringing the left mixture to cut-off. The student performed his memory items and then checklist items for Engine Failure in flight checklist. He then performed the Troubleshoot checklist and then Engine Feathering and Securing checklist. We maneuvered with the left engine feathered for a few minutes; performing normal level turns using normal banking maneuvers. I then told the student to use the Air Start Procedure to restart the engine in flight. The student performed the checklist and upon completion of the checklist the left engine remained in the feathered position. We completed the Engine Feathering and Securing checklist again and after a few minutes attempted the Air Start Procedure again. After completing the Air Start Procedure a second time the left engine remained in the feathered position. We completed the Engine Feathering and Securing checklist again. The student continued to fly the airplane towards the nearest suitable airport ZZZ. I [requested priority handling] with ZZZ Tower about 10NM to the north. We were cleared straight in for Runway XXR; I handled the checklist and radios while the student flew us towards Runway XXR. At about 5nm from ZZZ I took the flight controls from the student and made a normal straight in approach and landing on XXR. I was able to taxi us to the maintenance facility where we parked and shut down. Maintenance is currently inspecting the aircraft to determine a cause. One thing I could have done differently was to call maintenance on the radio in-flight and explain to them what happened and what we see/hear and they could possibly troubleshoot the problem for us from the ground before advising ATC.


Synopsis: Multi-engine flight instructor and student reported that during a simulated engine failure lesson they were unable to un-feather the propeller and returned to the departure airport for an uneventful landing. The flight Instructor stated they simulated the engine failure by moving the mixture control to idle cutoff.