What happened
During the landing phase of flight, the right main landing gear assembly collapsed upon contact with the runway surface. The failure occurred while the aircraft was transitioning from flight to ground contact.
The investigation
Examination of the collapsed gear assembly revealed that the rear trunnion pivot pin, identified by part number 5741112-1, had shifted aft and exited its designated housing within the trunnion. Visual inspection indicated approximately one inch of white paint on the end of this pin where it extended into the flap track area.
In contrast, the extension of the rear pivot pin on the left gear was measured at only half an inch of painted pin extending into the same area. The pivot pins are secured within the trunnion by a roll pin. Analysis showed that the aft pin still contained a section of this roll pin, and the mode of failure was determined to be a shear. Two additional small fragments of the roll pin were found remaining inside the trunnion.
Further inspection of the forward pivot pin revealed a distinct wear pattern indicating that the shims had been positioned approximately two-tenths of an inch further from the pivot pin hole compared to the rear pin. Additionally, grooved wear marks were observed on the rear pin extending all the way to its end, originating from the point where the initial wear pattern began.
Findings
The primary cause of the gear collapse was fuel exhaustion leading to a loss of hydraulic pressure or structural integrity due to improper maintenance. The misalignment and excessive wear on the pivot pins suggest that incorrect shimming during previous maintenance allowed for abnormal movement and subsequent shear failure of the roll pin securing the trunnion pivot.
Safety message
Proper installation and measurement of shims are critical to ensuring correct alignment of landing gear components. Maintenance procedures must verify that all pins extend correctly into their respective tracks to prevent premature wear and catastrophic failure.