N18555

According to the pilot/owner of the Beech F17D Staggerwing biplane, on the day of the accident, he took a passenger on a brief local flight, and then they returned for some landings and takeoffs. The winds were calm, and the first landing was uneventful. The pilot took off again, circuited the traffic pattern, and landed a second time. Shortly after touchdown, the airplane began to "sink." The pilot tried to raise the nose to offload the landing gear, and he shut down the engine, while the airplane continued to settle. The propeller struck the ground, and the airplane settled on the right lower wing before it came to a stop. The aft fuselage, propeller, lower cowl and outboard spar of the right lower wing were damaged. Postaccident examination indicated that the chain used to retract and extend the right main landing gear had fractured, which resulted in the partial retraction of the landing gear. According to maintenance records, the chain was installed new in the airplane in 1969, and it had accumulated approximately 910 hours in service. The pilot/owner estimated that the chain had accumulated 1,800 cycles, with each cycle consisting of one retraction and one extension. Visual examination revealed 29 fractures in the outer chain plates, and two completely fractured outer plates, not including the chain failure point. All fractures were oriented radially with respect to the link pivots. Every outer plate was stamped with the notation "ACME 40 SINGAPORE." The National Transportation Safety Board was unable to determine whether this failure mode was limited to this make and model chain. The airplane was manufactured in 1937, and the manufacturer had not established any time or cycle life limits for the chain.