On June 9, 1984, a Beech 99 (registration N320BA) was involved in an aviation accident near Chicago, IL. Investigators recorded the probable cause as: Fatigue crack in right main landing gear hydraulic actuator allowing loss of hydraulic fluid. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An aircraft's landing gear extended but failed to lock; crew could not rectify using normal or emergency procedures. Gear collapsed on touchdown. Investigation found a fatigue crack in the right main gear hydraulic actuator causing fluid loss. Maintenance checks had been performed 28 hours prior.
Incident Overview
During a landing, the aircraft's landing gear extended but did not lock into position. The flight crew attempted to resolve the situation by following both normal and emergency gear extension procedures, but these efforts were unsuccessful. Upon touchdown, the landing gear collapsed.
Investigation Findings
A post-incident investigation revealed that a fatigue crack had developed in the hydraulic actuator of the right main landing gear. This crack allowed hydraulic fluid to escape, which prevented the actuator from functioning correctly and thus the gear from locking. The loss of hydraulic fluid was identified as the direct mechanical reason for the gear's failure to lock.
Maintenance Background
According to maintenance records provided by the operator, the hydraulic actuators had been inspected for leaks and alignment approximately 28 flight hours prior to the incident. The inspection did not detect the fatigue crack or any other anomaly at that time.
Probable cause
Fatigue crack in right main landing gear hydraulic actuator allowing loss of hydraulic fluid.