Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 208; Flight Crew Total 1190; Flight Crew Type 524
Situational Awareness; Confusion; Training / Qualification; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Human Factors; Procedure; Aircraft
I flew with two of my students to a distant airport. I began the flight as usual with a preflight and a ground check before taking off. I flew with my first student direct and did three practice approaches before landing. The flight down went without any abnormalities. During the flight all engine instruments were in the green arc.On the ground after landing we ran through the Shutdown checklist. When we moved the mixture to idle cutoff; the engine did not completely shut down. The engine ran very rough and was obviously still getting enough fuel to keep it from shutting down but not enough to create any power. I then shut the engine off by turning off the magnetos. My thoughts were that the mixture cable needed to be readjusted because idle cutoff was not completely cutting off fuel to the cylinders. As we started up the engine for the remainder of the flight with the second student; the engine started normally and the ground check was normal. We took off and did three practice approaches at that airport before returning to our home base. During the return flight all engine instruments were in the green arc and the engine ran normally.We landed without incident; but when we ran the Shutdown checklist; idle cutoff gave us no noticeable difference in power change and the engine still ran like I had not changed the mixture setting at all. I did not want any fuel to be left in the cylinders after I shut the engine down; so I turned off the fuel selector to shut down the engine. I then notified maintenance through dispatch of our squawk. Later; I learned that the mixture cable did not just need to be readjusted but it had broken. I am very aware of how serious the issue could have become.I believe that several human factors could have played a role to why I chose not to stop at the out station and report the issue. The night before; I had only slept for about three hours because my schedule began at a much earlier time than it normally does. I was working a sixth day and with the combination may have been suffering fatigue. I believe I also had a hazardous attitude of invulnerability in which I thought I knew what the problem was and didn't think anything bad could happen because of it. The combination of these factors led to poor decision making.To prevent something like this from happening again; I plan to pay very close attention to the amount of sleep I get each night before flying so that I can be sure to have an alert mind. I also plan to always contact our dispatch so that I can speak with maintenance about any abnormality or issue before continuing any flight no matter how minor I may think it is at the time.
After the engine did not shut down with the Mixture OFF on two occasions; Maintenance determined the Mixture cable failed and did not control the engine.