What happened
During the flight phase, the crew observed a decrease in the quantity of utility hydraulic fluid. In response, the engine-driven pumps were shut off and remained off until just before landing. After extending the landing gear and flaps, the quantity indicator showed 3.5 gallons remaining, with all pressures reading normal. Following touchdown, the #1 reverser light was slow to illuminate. Reportedly, reverse thrust on the #1 and #4 engines was delayed until all reverser lights were confirmed on.
The landing roll proceeded normally until the aircraft slowed to approximately 80 knots, at which point it began veering to the right. The captain reported a lack of left braking authority and no nose wheel steering. The aircraft continued off the runway, resulting in the collapse of the left main gear. After the aircraft stopped, fire bottles were discharged after smoke was observed emanating from the #1 engine.
The investigation
Investigation of the scene revealed left and right tire marks measuring 1245 feet and 870 feet in length, respectively, both showing signs of intermittent intensity. When the utility hydraulic system was first powered by the auxiliary pump, the nose wheel steering and spoilers operated correctly. A physical examination of the landing gear identified a stress corrosion crack where the left main gear sidebrace had failed.
Findings
The failure of the left main gear sidebrace due to stress corrosion cracking contributed to the collapse of the landing gear during the off-runway excursion.