Incident Overview
During a landing approach, the flight crew observed that the nose landing gear and main body landing gear indicated as up and locked after a normal gear extension attempt. The crew then executed the alternate gear extension procedure, which also proved unsuccessful. With fuel reaching the minimum required state, the aircraft landed with the nose and main body gear still retracted.
Post-Inspection Findings
A subsequent examination of the aircraft uncovered that the selector valve for the affected landing gear was positioned in the up-and-locked configuration. The bolt that connects the valve arm to the cockpit control cable system was missing. Additionally, the bolt for the wing gear selector valve arm was found partially backed out, and its nut and cotter pin were absent.
Maintenance History
The aircraft had been delivered to United Airlines in January 1990 and had accumulated 2,952 flight hours and 402 cycles at the time of the incident. A thorough review of the maintenance records revealed that no maintenance had been performed on the landing gear system since delivery.
Alternate Extension Procedure
It was noted during the investigation that a second alternate gear extension procedure—which involves de-energizing the hydraulic system for the affected gear—was not published in the crew operating manuals, not taught during initial training, and not included on any checklist available to the flight crew.