What was found
DURING FLIGHT, PILOT HEARD A LOUD BANG FROM THE FRONT OF THE AIRCRAFT. NOSE GEAR DOWN LIGHT ILLUMINATED. WAS UNABLE TO RETRACT NOSE GEAR. ELECTED TO LAND. DURING INSPECTION, FOUND BOLT, NAS464PA13, THAT ATTACHES NOSE GEAR RETRACT CYLINDER TO THE AIRFRAME HAD SHEARED. WHEN THIS HAPPENED, THE FORCE OF THE EXTEND ASSIST SPRINGS EXTENDED AND LOCKED THE NOSE GEAR DOWN. RECOMMEND INSPECTION OF GEAR RETRACT CYLINDER BOLTS AT ANNUAL INSPECTION. REPLACEMENT ON A 5 OR 10 YEAR SCHEDULE. THE NAS 464P3A13 BOLT IS A SHEAR BOLT.