What happened
On March 18, 2002, at 22:20 local time, a Boeing 727-100, registration PP-VLV, operated by VARIGLOG, was performing a scheduled cargo flight from Salvador to Confins. The crew, consisting of two pilots and one flight mechanic, was executing a stabilized approach to runway 16 under favorable visual night conditions.
During the final approach, the pilot reported hearing an unusual noise and noted that the aircraft felt "unbalanced." Although the landing gear indicators showed the gear was down and locked, the left main landing gear assembly had already begun to fail. Upon touchdown, the left main landing gear collapsed and separated from the aircraft, striking the number one engine. The impact caused the aircraft to veer off the runway, resting on its left wing. The aircraft sustained severe damage to the fuselage, left wing, and left flap, rendering it a total loss.
The investigation
CENIPA investigators examined the wreckage and conducted metallurgical analysis of the fractured components at Boeing Materials Technology. The investigation focused on the left main landing gear's lower side strut segment assembly and the trunion link assembly.
Technical analysis revealed that the trunion link had fractured in multiple sections. Specifically, investigators identified "beach marks" on the anterior end of the trunion, which are characteristic indicators of slow-growing fatigue cracks. The origin of this crack was traced to a machine groove located on the internal face where the drag strut socket meets the trunion web. This groove was found to be inconsistent with the aircraft's design specifications and maintenance manuals. Scanning Electron Microscopy (SEM) confirmed that the fracture originated from multiple fatigue sites along this groove, interspersed with stress corrosion cracking.
Findings
- The primary cause of the landing gear collapse was a fatigue crack originating from a machine groove on the trunion link assembly.
- The machine groove, which was not part of the original design, likely occurred during material handling or maintenance and went undetected during routine inspections.
- The presence of the groove facilitated the initiation and propagation of the crack through fatigue and stress corrosion.
- The aircraft's structural integrity was compromised prior to touchdown, as evidenced by the pilot's observation of an unbalanced flight path during the final approach.
- The aircraft was determined to be economically unrecoverable due to the extent of the structural damage.