C172 INSTRUCTOR HAS LOSS OF ENG PWR AND MAKES AN OFF FIELD LNDG.

Narrative

THE C172 ACFT I WAS INSTRUCTING IN; SUFFERED A LOSS OF ENG PWR WHILE IN CRUISE FLT. I ASSUMED CTL OF THE ACFT; ATTEMPTED TO REESTABLISH ENG PWR WITH THE APPROPRIATE CHKLIST. ADJUSTING THE THROTTLE YIELDED NO CHANGE IN ENG PWR. DUE TO AN OVCST LAYER AT 3000 FT MSL; WE WERE FLYING AT 2500 FT MSL (APPROX 1500 FT AGL). WITH THE ACFT OPERATING AT IDLE PWR ONLY I HAD NO CHOICE BUT TO INITIATE AN OFF-ARPT LNDG. I MADE A 'MAYDAY' CALL ON 121.5 AND SQUAWKED 7700. I WAS ABLE TO SELECT A SMOOTH DRY FIELD ORIENTED INTO THE WIND AND MADE AN UNEVENTFUL LNDG IN A WHEAT FIELD. THE ACFT CAME TO REST UNDAMAGED AND NEITHER I NOR MY STUDENT WERE INJURED. I CONTACTED A COMMERCIAL AIRLINER ON 121.5 WHEN THE ACFT HAD COME TO STOP AND REQUESTED THAT HE RELAY TO ZKC THAT THE ACFT WAS UNDAMAGED AND THE OCCUPANTS UNINJURED. MY STUDENT MADE A FOLLOW-UP PHONE CALL WITH COLUMBIA FSS INFORMING THEM OF OUR STATUS. MY STUDENT AND I DE-COWLED THE ACFT SHORTLY AFTER LNDG AND WE WERE ABLE TO DETERMINE THAT THE THROTTLE CABLE HAD BECOME DISCONNECTED FROM THE CARB. THE ACFT WAS ABLE TO MAINTAIN 'IDLE' PWR ONLY AND NO INPUT FROM THE PLT IN THE COCKPIT COULD HAVE RESTORED ENG PWR. THE ACFT HAD RECENTLY UNDERGONE AN ANNUAL INSPECTION. THIS WAS THE ACFT'S SECOND FLT FOLLOWING ITS ANNUAL INSPECTION. THE ACFT OWNER INFORMED ME THAT THE THROTTLE CABLE AND ATTACHMENT ASSEMBLY HAD BEEN REPLACED DURING THE ANNUAL INSPECTION.