What happened
On January 10, 2010, an Airbus A319-131, registration N816UA, operated by United Airlines, landed on runway 4L at Newark Liberty International Airport with its right main gear partially extended. The flight, arriving from Chicago O'larie, experienced an abnormal gear indication during the approach to runway 4R.
After the crew attempted to extend the gear and observed that the right main gear remained in a red (not down and locked) state, they performed a go-around. The crew attempted a gravity extension of the landing gear, but the right main gear failed to lock. Due to fuel considerations, the crew decided to proceed with the landing.
During the final approach, the captain elected to shut down the engines prior to touchdown. The aircraft touched down on the left main gear and nose wheel, while the right engine nacelle made contact with the runway. The aircraft came to rest approximately 3,400 feet from the initial touchdown point. During the subsequent evacuation, 3 passengers sustained minor injuries, while the 5 crew members were not injured.
The investigation
Investigators examined the right main landing gear door actuator and found that the right main gear door was in a partially open position, which obstructed the gear from fully extending.
Detailed analysis of the actuator revealed that internal components had failed, producing significant amounts of metallic debris. This debris, consisting of both ferrous and bronze-colored particles, was found inside the cylinder and the retract restrictor. Testing indicated that the debris likely restricted fluid flow, which would reduce the speed of the actuator's movement and prevent the door from reaching the fully open position.
Regarding the evacuation, the 1R door did not fully open, and the emergency evacuation slide failed to deploy. While the crew noted resistance when arming the door prior to the flight, investigators found no mechanical defects in the door or the power assist actuator. The failure of the slide to deploy was attributed to improper packing of the 1R slide.
Findings
- The right main landing gear door actuator suffered a mechanical failure of internal components.
- Metallic debris within the actuator likely restricted hydraulic fluid flow, preventing the gear door from opening sufficiently to allow the gear to lock.
- A circular reference existed in the airline's Flight Manual, where the Landing Gear Gravity Extension checklist referred the crew back to the Landing Gear Unsafe Indication After Extension checklist instead of the appropriate landing procedure.
- The decision to shut down the engines in the flare, while not the cause of the gear failure, resulted in the loss of electrical power to the flight data recorder and cockpit voice recorder just prior to touchdown.