What happened
The flight crew encountered a mechanical issue during the approach phase of the operation, specifically regarding the landing gear system. The aircraft was unable to lower and lock its nose gear into the down position. As a result, the crew executed an emergency procedure that involved making a nose gear up landing. This maneuver allowed the aircraft to touch down safely on its main landing gear and fuselage structure, avoiding a catastrophic failure of the undercarriage during touchdown.
The investigation
Following the incident, investigators conducted a thorough examination of the aircraft's landing gear mechanism. The initial inspection determined that the nose gear drag brace was physically locked in the up position, preventing extension. To understand why this occurred, the drag brace assembly was removed and disassembled for closer scrutiny.
The disassembly revealed that the link assemblies, which serve to connect the locking pawls to the locking actuator, had suffered structural failure. A metallurgical examination of these failed components identified corrosion cracking as the primary mechanism of failure. Further analysis traced the origin of this corrosion to an electrolytic reaction occurring between the metal composition of the bushing within the link and the metal of the link itself.
Findings
A detailed inspection of the bushings installed in the link assemblies uncovered a critical manufacturing deviation: the absence of required protective coatings. Specifically, the bushings lacked both cadmium plating and chromate coating. These protective layers are essential for preventing galvanic corrosion between dissimilar metals.
The investigation determined that these bushings were procured by Eastern Airlines from an external vendor. The vendor was manufacturing the parts using technical plans supplied directly by Eastern Airlines. However, the specific plans provided by Eastern failed to specify or mandate the necessary cadmium plating and chromate coating requirements for these components, leading to the installation of unprotected bushings that eventually failed due to environmental exposure.