Primary finding
Probable cause
Failure of the aircraft operator maintenance personnel to adequately lubricate and seal the main landing gear bogie beam swivel joint as required by manufacturer and operator maintenance program requirements. This allowed moisture to enter the swivel joint and cause corrosion damage which caused stress corrosion cracking and failure of the swivel joint lugs. Contributing to the incident was lack of clear instructions in the operators maintenance program regarding lubrication of the swivel joint.
Investigator assessment
Analysis narrative
Aircraft experienced collapse of the left main landing gear bogie while stopped at the runway awaiting takeoff clearance. Postincident examination indicated the aft bogie swivel joint lugs had failed due to stress corrosion cracking. The swivel joint did not have proper lubrication which keeps water out. This allowed formation of corrosion on the surface of the lugs, and subsequent crack initiation at the corrosion pits. Operator maintenance requirements specified that the swivel joint be lubricated every weekend check and every 'a' check. The work cards for these two inspections called out in narrative form the lubricating of the bogie pivot joint. The cards called for the swivel joint to be lubricated by reference to a number on an illustration. The failure of the swivel joint lugs was the subject of DOUGLAS aircraft all operator letters in 1976 and 1990. These letters stressed to operators the importance of lubricating the swivel joint to prevent corrosion formation.
Source record
Factual narrative
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