What was found
AN AIR TRACTOR AT802A WAS INVOLVED IN A TAKE-OFF INCIDENT, CAUSING SUBSTANTIAL DAMAGE. THE PIC LOOKED TO HIS LEFT AND RIGHT DURING TAKEOFF AND NOTICED THE FLAPS WERE RETRACTING UNCOMMANDED AFTER SELECTING 20 DEGREES FOR TAKEOFF. ASI DISCOVERED THAT THE FLAP ACTUATOR ASSEMBLY COUPLING, PART NUMBER B100-06, WHICH SERVES AS THE CONNECTION BETWEEN THE ELECTRIC FLAP MOTOR AND THE ACTUATOR LYING AT THE BOTTOM OF THE AIRCRAFT, WAS BROKEN. UPON EXAMINATION, IT WAS FOUND THAT THE METAL KEYS WITHIN THE COUPLING HAD SHEARED OFF, LEADING TO THE FAILURE OF THIS CRITICAL COMPONENT. ACCORDING TO AIR TRACTOR SERVICE LETTER (SL) 260, WHICH PROVIDES DETAILED INFORMATION REGARDING THE FLAP ACTUATOR COUPLING, THE MANUFACTURER RECOMMENDS REPLACING THE COUPLING AFTER 400 HOURS OF OPERATION. HOWEVER, IN THIS INSTANCE, THE COUPLING FAILED AT 575.7 HOURS, SIGNIFICANTLY EXCEEDING THE RECOMMENDED REPLACEMENT INTERVAL.