Incident Overview
While climbing through flight level 200 (FL200), the flight crew experienced a loss of pressure in the #4 hydraulic system. The red "GEAR DOOR" and "LEFT WING DOOR OPEN" lights illuminated. A medium-frequency vibration and a loud rushing sound were also noted. The flight diverted to Miami, Florida, where a landing was made without further incident.
Investigation Findings
Subsequent examination disclosed that the left wing landing gear door actuator, the actuator beam assembly, and associated keel beam box attaching hardware were missing. The absence of these components was identified as the source of the hydraulic system pressure loss and the associated warnings.
Manufacturer Response
Following the incident, Boeing issued a service bulletin concerning the detection of cracks in the internal back-up brackets and fittings for the wing gear door actuating system. The bulletin provides guidance for inspecting these components to prevent similar occurrences.