Incident Overview
A hydraulic fluid leak from a deteriorated O-ring in the landing gear selector solenoid valve rendered the normal landing gear extension system inoperative. The flight crew initiated the alternate gear extension procedure in an attempt to lower the landing gear. However, the right main landing gear did not extend.
Alternate Extension Attempt
During the alternate extension, the first officer pulled the main landing gear alternate extension cable until it stopped, but the right main landing gear uplock actuator did not release. Following guidance from company maintenance, the crew retracted the nose gear and left main gear using the normal system and then attempted another normal extension. Only the left main landing gear extended. The aircraft's number 2 hydraulic system was nearly depleted, with only 1.5 quarts of fluid remaining.
Subsequent Actions and Landing
The crew attempted to retract the left main landing gear again, but without success. The captain then performed a landing with only the left main landing gear extended.
Post-Incident Examination
Inspection of the alternate gear system revealed that the main gear extension cable would bind after the left main landing gear uplock actuator released. Subsequent testing with the aircraft on jack stands reduced the binding, but in all tests, the left main landing gear uplock actuator released before the right uplock actuator. Examination of the main gear alternate extension cable showed that the plastic coating was missing in two locations adjacent to a pulley. The right main landing gear wheel well was excessively dirty, with areas of exfoliated white paint exposing the underlying primer.