EMER FORCED LNDG AT NON TWR ARPT WHEN SMA'S ENG GOES TO IDLE PWR AFTER PWR APPLICATION FAILS.

Narrative

I WAS PERFORMING A BIENNIAL FLT REVIEW ON A PERSON WHO OWNED HIS OWN PLANE. HE HAD JUST HAD THE ANNUAL ON THE ACFT; AND THIS WAS THE FIRST FLT AFTER THE INSPECTION. WE DEPARTED OSU ARPT AND PROCEEDED TO THE PRACTICE AREA. AFTER PERFORMING MINIMUM CTLABLE AIRSPD; STALLS; STEEP TURNS; I INITIATED A SIMULATED ENG FAILURE BY RETARDING THE THROTTLE AND APPLYING CARB HEAT. AFTER THE OWNER SUCCESSFULLY AND APPROPRIATELY ACCOMPLISHED THE ENG OUT CHKLIST; I TOLD HIM TO BREAK OUT OF THE MANEUVER AND HEAD FOR DLZ. APPLICATION OF PWR YIELDED NO RESULTS. FORTUNATELY WE WERE WITHIN GLIDING DISTANCE OF DLZ. WE ACCOMPLISHED AN INCIDENT-FREE ENG OUT LNDG AT DLZ. THE OWNER CONTINUED TO FLY THE PLANE WHILE I ADVISED TFC AND OBSERVED HIS ACTIONS. THE ENORMOUS TIME WE SPEND PRACTICING ENG OUTS MADE THE REAL THING SEEM 'EASY.' MAINT DISCOVERED THE COTTER PIN WAS MISSING FROM THE THROTTLE LINKAGE TO THE CARB; CAUSING THE NUT TO FREE ITSELF; AND CONSEQUENTLY; LEAVE US WITH IDLE PWR ONLY. PLT ERROR; THIS WAS NOT.