What happened
During the approach to runway 27L, with winds from the southwest at 15 knots and no gusts, the pilot confirmed that all landing gear were down and locked via the cockpit indicator lights. The aircraft touched down on the left main landing gear, followed by the right main and then the nose gear. During the landing roll, as the aircraft was nearly stopped, the pilot experienced a sensation similar to a blown tire. The right wheel began to zigzag, leading to a loss of directional control to the right and the subsequent collapse of the landing gear. The aircraft came to rest upright.
The investigation
Post-incident examination of the aircraft revealed scrubbing on the lower inboard portion of the right main landing gear tire. The right main landing gear wheel assembly had rotated nearly 90 degrees, and the upper and lower link assemblies had separated from one another, with the attachment hardware remaining in the upper link assembly.
Investigators found that the bolt securing the upper and lower link assemblies had pulled through the lower link assembly at the nut end. Two washers on the nut end, measuring approximately .023 inch thick, were damaged during this pull-through event. A washer measuring approximately .061 inch thick had been installed under the bolt head. While a non-mandatory Cessna Service Information Letter recommends installing .066 inch thick washers on both the head and nut ends of this bolt, there was no maintenance record indicating compliance with this letter.
Further testing of the right main landing gear actuator revealed that the unlocking pressure was too high and one of the four lock keys had been improperly installed. Although the operator had tested the actuator for unlock pressure approximately two months prior in accordance with a service bulletin, the actuator was not replaced despite the bulletin requiring replacement if pressures were out of specification. There was no serviceable tag in the maintenance records, and there was no documentation regarding when or where the actuator had been overhauled. Additionally, the operator's FAA-approved inspection program did not include inspections of the main landing gear link assemblies, unlike the Cessna Progressive Care Program.