Incident Details
The pilot and copilot reported that during approach, they observed three green lights indicating the landing gear was extended after passing the outer marker. Hydraulic pressure was approximately 1,000 psi during landing checks. The pilot landed the airplane with a slight tailwind, observed two beta lights, and moved the power levers into ground idle/reverse. Shortly after, the left landing gear collapsed. The pilot observed one red unsafe light and two green landing gear lights, accompanied by a gear warning horn.
Postaccident Examination
Examination of the left main landing gear revealed a fractured piece from the inboard gear-forging boss, which houses a clevis for the attachment of the hydraulic cylinder. The clevis remained attached to the hydraulic cylinder, which in the fully extended position is consistent with the gear being down. Metallurgical analysis of the fracture surfaces indicated features typical of overstress separation. No pre-existing cracks or other defects were found on the fracture.
Maintenance History
A review of the Commander maintenance manual states that an adjustment must be made to the cylinder over travel following gear maintenance to obtain the proper drag brace preload. The left hydraulic cylinder, main landing gear aft wheel well door, and hydraulic components were replaced approximately 34 hours before the accident.