What was found
WHILE FLYING A FIRE MISSION IN SUPPORT OF USFS, THE PILOT NOTICED THE RT GEAR START TO EXTEND FOLLOWED BY A LOSS OF HYDRAULIC PRESSURE. PILOT RETURNED TO THE AIRPORT AND LANDED. THE PROBLEM WAS TRACED TO THE RT MAIN GEAR RETRACT CYLINDER. UPON DISASSEMBLY OF THE RETRACT CYLINDER, THE O-RING AROUND THE SHAFT WAS FOUND TO BE SPLIT. THE SPLIT O-RING ALLOWED THE HYDRAULIC FLUID TO BE PUMPED OUT. THE SEALS AND O-RINGS WERE REPLACED. PROBABLE CAUSE: POSSIBLE DIRTY SHAFT ALLOWING FOREIGN MATERIAL TO SPLIT THE O-RING. PILOT WAS ADVISED TO MAKE SURE SHAFTS ARE KEPT CLEAN. (S)