A DHC-8-402Q Dash 8, JA849A, sustained substantial damage in a landing accident at Kochi Airport (KCZ), Japan. There were 56 passengers and four crew members on board. There were no injuries. All Nippon Airways flight 1603 took off from Osaka (ITM) at 08:21 on a regular domestic flight to Kochi. At 08:47 the flight was given clearance to land on runway 32. However, when configuring the aircraft for landing, it appeared that the nose landing gear would not deploy. The approach was abandoned and the airplane entered a holding pattern. The crew members attempted to deploy the nose undercarriage but the attempts failed. Two low passes were flown, at 500 feet over the runway. The crew then attempted to extend the nose landing gear by utilizing acceleration force during a steep turn. When this did not work, a touch-and-go was made so as to apply an impact to the nose landing gear. The flight crew when concluded that they had to make a landing with the nose gear retracted. The captain directed the cabin attendants to move some passengers to aft cabin and fire extinguishing agent was sprayed on the runway. At 10:54 a landing was carried out. The airplane sustained structural damage on the lower part of the forward fuselage. PROBABLE CAUSE: “It is recognized that this accident was caused by that, in spite of gear down operations in flight by normal and alternative procedures, the nose landing gear could not be extended because the doors of the nose landing gear remained closed, and when the Aircraft landed in this configuration, the lower part of the forward fuselage contacted the runway surface and was damaged. It is recognized that the doors of the nose landing gear remained closed because the spacer migrated out from the hinge part of the toggle link assy, which was part of the nose landing gear door linkage mechanism, interfered with the support fitting, thereby prevented the movement of the toggle link assy, which resulted in restraining the movement of the entire nose landing gear door linkage mechanism. It is estimated that the spacer migrated out because the bolt, nut and the like were not installed, and the spacer was gradually pulled aft out of the toggle link assy under the influence of retractions/extensions of the nose landing gear, airframe vibration, aircraft acceleration and so on, during operations of the Aircraft. Regarding that the bolt, nut and the like were not installed, it is considered that these parts were not re-installed at the time of the repair in the manufacturing process of the Aircraft.”