What was found
OWNER COMPLAINED OF POWER LOSS DURING LEVEL OFF AND FLARE AFTER DESCENT. HE INSISTED THERE WAS NO "NEEDLE SPLIT". IN SPITE OF THAT, I SUSPECTED AN ISSUE WITH THE OVERRUNNING (SPRAG) CLUTCH. I FLIGHT TESTED AND ALL APPEARED NORMAL. AFTER CHECKING EVERYTHING THAT COULD CAUSE AN INTERMITTENT, TEMPORARY POWER LOSS INCLUDING ENGINE AND GOVERNOR SYSTEMS AND ELIMINATING ENGINE AND ASSOCIATED SYSTEMS AS A POSSIBLE CAUSE, I FLIGHT TESTED THE AIRCRAFT AGAIN CONCENTRATING ON POWER RECOVERY FROM AUTOROTATIVE DESCENT. ON THE THIRD AUTOROTATION DESCENT WITH NEEDLES WELL SPLIT I INITIATED A GENTLE POWER RECOVERY. THE OVERRUNNING CLUTCH FAILED TO LOCK BACK UP WHEN NEEDLES WERE JOINED. I ROLLED THROTTLE BACK OFF AND REJOINED THE NEEDLES VERY CAREFULLY, ROCKING THE THROTTLE AS THE NEEDLES REJOINED. THE CLUTCH LOCKED BACK UP AND I WAS ABLE TO COMPLETE A NORMAL LANDING BEING EXTREMELY CAREFUL NOT TO ALLOW ANOTHER NEEDLE SPLIT. I HAD PREVIOUSLY (DURING INITIAL TROUBLESHOOTING) DRAINED AND INSPECTED THE SPRAG CLUTCH FLUID. IT SHOWED NO EVIDENCE OF METAL PARTICLES. WE THEN INSTALLED A OVERHAULED CLUTCH ASSEMBLY INCLUDING A NEW SPRAG CLUTCH. PROBLEM SOLVED. ROBINSON HELICOPTERS IS INVESTIGATING THE CAUSE OF THE FAILURE.