What was found
DURING LANDING, NOSE GEAR EXTENDED AND LOCKED, BUT MAIN GEAR DID NOT LOCK INTO PLACE. PILOT TRIED TO LOCK MAIN GEAR USING HAND HYDRAULIC PUMP WITH NO SUCCESS. AIRCRAFT LANDED WITH LOCKED NOSE GEAR AND COLLAPSED MAIN GEAR. SUFFERED DAMAGE TO REAR OF FUSELAGE, LEFT ELEVATOR, AND LEFT HORIZONTAL STABILIZER. INVESTIGATION FOUND FAILED NOSE GEAR HYDRAULIC FLEX LINE. THE FAILURE OF THIS LINE ALLOWED EXHAUSTION OF LANDING GEAR HYDRAULIC FLUID AFTER THE NOSE GEAR EXTENDED AND LOCKED, PREVENTING THE MAIN GEAR FROM LOCKING INTO PLACE.CONDITIONAL PART FAILURE. NO HISTORY NOTED IN AIRCRAFT MAINTENANCE RECORDS ASSOCIATED WITH NOSE GEAR HYDRAULIC HOSE REPLACEMENT SINCE 1976.