Boeing 737-8 N27290 accident near Houston, Texas

Probable cause

The captain's decision not to establish and maintain deceleration devices in accordance with company training and standard operating procedures.

NTSB analysis

United Airlines flight 2477 departed taxiway SC while turning off of runway 27 at high speed after landing at George Bush Houston Intercontinental Airport (IAH), Houston, Texas. As flight 2477 departed the paved taxiway, the left main landing gear impacted a concrete structure recessed in the ground adjacent to taxiway SC. This impact resulted in separation of the left main landing gear. Postaccident examination of the airplane found nothing anomalous that precluded normal operation of the landing gear and the wheel braking system. Furthermore, the flight crew reported no anomalous operation of the autobrake system, the speedbrake system, or the thrust reversers during the landing rollout.

The captain stated, and the flight data recorder (FDR) data confirmed, that he retracted the speedbrakes about 6 seconds after landing in order to turn off the autobrakes. Additionally, only engine idle reverse thrust was used after touchdown. By not using maximum reverse thrust upon touchdown and by turning off the autobrakes shortly after landing, the captain failed to follow multiple company standard operating procedures (SOPs) that would have assured deceleration of the airplane. The captain delayed application of maximum manual wheel braking after turning off the autobrakes, and the airplane remained at high speed as it neared the end of the runway.

Speedbrake deployment increases wing aerodynamic drag and reduces wing aerodynamic lift, thereby slowing the airplane and increasing main landing gear wheel loading for more effective wheel braking. By stowing the speedbrakes shortly after landing, the wheel brakes were less effective in decelerating the airplane when the captain eventually applied maximum manual wheel braking. Had the captain used timely and effective manual wheel braking with the speedbrakes deployed, the airplane would have been capable of decelerating to a safe taxi speed before exiting the runway.

The flight crew did not conduct a thorough briefing of the airplane’s landing performance when the captain changed the autobrake setting from 2 to 1, which decreased the target deceleration rate for the autobrake system. Furthermore, the flight crew did not effectively discuss potential threats, such as the wet runway condition, and appropriate threat mitigations in an arrival briefing. When the captain changed the autobrake setting to 1, the first officer (FO) accepted this deviation from the established autobrake SOP without further discussion, missing an opportunity to exhibit good crew resource management by discussing potential risks associated with this action. Lastly, a thorough arrival briefing could have identified and reminded the flight crew of a paved blast pad within the normal runway safety area (RSA) at the end of runway 27. This blast pad and RSA infrastructure provided an opportunity to decelerate to a safe taxi speed for full stop on paved and non-paved, obstacle-free surfaces instead of attempting to turn onto taxiway SC at high speed.

Text from the NTSB. Open the NTSB docket for DCA24FA120 for the full record.