My longest and dearest friend is one of the top engine mechanics I've ever met. And he does it as a hobby. Anyway, he has always smiled and nodded knowingly when I've extolled the virtues of fight simming in general and fsX specifically.
That is until I told him about my trials and tribulations keeping my new Spitfire running. I asked if he or his dad could work on an old Merlin 12 cylinder and he nodded again and said, "Sure, if it's got a crankshaft I can get it running just fine."
Last night, he came by to drop off some computer stuff and said "Okay where's this Merlin you were ranting about?" I fired up the Spitfire, got her up and let her "do her thing" within a couple minutes she was smoking, coughing and I barely got her back on the ground before everything died.
I pulled her into the hanger, opened up the various option windows and told him, "There you go -- fix it."
Two hours later he emerged with a huge smile on his face saying that was some of the best fun he'd ever had.

He uses the old "shade tree mechanic" approach and tinkers with each little bit, cylinder by cylinder, component by component until he had her running like a fine watch. He was amazed at the level of detailing and control Accu-Sim affords the user -- especailly a seasoned engine mechanic.
Unfortunately, you should never let the crew chief actually try and fly the plane. He crashed on take off and had to do it all over again.
As he left for the night, he smiled and said,"I'll be over next week and tackle that P-40 ya have."