NTSB report on United Airlines plane skidding off runway at Bush Airport

The National Transportation Safety Board has released a report on their investigation of the United Airlines plane skidding off the taxiway at Houston George Bush Intercontinental Airport.

On March 8, United Airlines flight reports UA2477 landed and the Boeing 737 Max exited the taxiway into a grassy area.

NTSB claims the left main landing gear (MLG) departed the paved surface and contacted a concrete structure that was recessed into the ground, resulting in its separation.

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The flight which departed from Memphis had 160 passengers and six crew members onboard, United Airlines says.

In the report, it was discovered, initially, that the touchdown was "uneventful, at an appropriate speed, and within the touchdown zone."

Shortly after landing, the airplane slid off the runway and the left main landing gear tires and nose wheels tires entered the grass before the airplane came to a rest with its left wing low. 

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Courtesy of National Transportation Safety Board

Authorities investigated the site and found the tires hit a large concrete "manhole" designed as an electrical junction box for lights/utilities at the airport. Due to this hit, the left MLG separated from the plane at the fuse pins near the rear spar, as designed, to prevent more severe damage to surrounding structures.

However, prior to this, it was reported the captain of the plane became concerned after the runway awareness and advisory system (RAAS) alert indicated 1,000 ft of runway distance remained even after he applied the brakes manually using the toe brakes at about 6,000 feet from the end of the runway. He reportedly felt as if the deceleration was less than normal.

Investigators state, "DFDR data and automatic dependent surveillance-broadcast (ADS-B) data indicated that after the disabling of the auto brakes occurred, manual braking did not begin until the airplane was about 4,000 feet from the end of the runway."

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The captain applied more pressure to the brakes and attempted to turn onto taxiway SC, by using the steering tiller and rudder pedals while pushing aggressively on the brake pedals. 

While turning into the taxiway, he told NTSB officials he felt the fuselage and rudder/brake pedals begin to shake violently and briefly released the brake pressure and the shaking ceased.

He reapplied aggressive brake pressure and the shaking continued before sliding off the runway.

NTSB investigators report from surveillance video, that the runway and taxiway surface conditions were wet.