Incident Overview
A hydraulic line (part number 137311D1443) in the main hydraulic system failed. The captain and first officer made numerous attempts to extend the landing gear using the emergency checklist and the aircraft flight manual. Two of the three landing gear legs were extended, but the pilots were unable to extend the left main landing gear. Subsequently, the aircraft was damaged during landing.
Hydraulic System Details
The failed hydraulic line was curved and measured approximately 15 feet from end to end. It had failed at the base of a flared fitting. This failure allowed hydraulic fluid in the main system reservoir to be pumped overboard.
The emergency hydraulic system had a three-position selector: NORMAL, FLAPS DOWN, and GEAR DOWN. Tests of the gear extension system revealed it worked properly when following instructions from the emergency checklist. However, with the selector in the NORMAL position, the line failure allowed fluid to be pumped from the emergency reservoir to the main system.
Metallurgical Examination
A metallurgical examination revealed that the hydraulic line had failed from multiple fatigue origins on the outside diameter of the tube and on diametrically opposite sides.
Service Bulletin
Later, British Aerospace issued a service bulletin (23-JM-8170) to reinforce the hydraulic line.