The National Transportation Safety Board (NTSB) has released its final report on the American Airlines Boeing 737 runway overrun incident at Dallas/Fort Worth International Airport (DFW) on February 10, 2024, concluding that improper maintenance had diminished the aircraft’s braking system performance.

American Airlines Flight 1632, with 98 passengers and six crew members onboard, failed to slow down sufficiently while landing at DFW, turning a normal touchdown into a braking emergency. The 737-800 overran Runway 17L before it was stopped by the airport’s Engineered Materials Arresting System (EMAS), with no one harmed during the incident.

Final Report On Flight AA1632 Runway Overrun

Credit: American Airlines

The NTSB stated the probable cause of last year’s incident as human error during a braking system modification, while citing the failure to conduct a proper post-modification check as a contributory factor. The aircraft had undergone a brake system modification just four days before the incident, but technicians made an error when reconnecting flexible hydraulic lines, severely reducing its braking power.

Additionally, a discrepancy was found in the wiring of the left main landing gear wheel speed transducers. It was discovered that the inboard and outboard sensor wires had been swapped, causing the antiskid system to receive incorrect data. These factors meant that both the left and right main landing gear were compromised in their braking performance, causing the 737-800 to overshoot the runway.

According to the NTSB’s final report,

“Improper maintenance due to human error during a braking system modification diminished braking performance. Contributing to the diminished braking performance was the lack of a functional check to verify the flexible hydraulic hoses and transducer wiring were connected correctly after the braking system modification.”

Brake System Modification Maintenance

Credit: NTSB

On February 6, 2024, the aircraft completed a scheduled modification to its braking system in accordance with Boeing Service Bulletin SB 737-32-1429, Revision 4. This involved replacing its original steel brakes with carbon brakes and installing four new flow limiters, which are designed to regulate brake fluid flow and ensure even braking across each wheel.

However, this process involved disconnecting each flexible hydraulic line and then reconnecting it after installation. During this stage, technicians accidentally reconnected flexible hydraulic lines to the wrong ports, meaning that hydraulic pressure was not being delivered correctly. Another error was made when the speed transducer wires for the inboard and outboard wheels were incorrectly swapped, further diminishing brake effectiveness.

The aircraft involved was a 15-year-old Boeing 737-800 (registration: N991AN) delivered to American Airlines in June 2009. The jet would ultimately return to service over a week after the runway overrun incident. The Boeing 737-800 is the largest single aircraft type in American Airlines’ fleet, with the carrier operating over 300 airframes. N991AN can seat up to 172 passengers in two cabin classes, but only had 98 passengers onboard during this incident.

American Flight 1632 On February 10, 2024

Credit: Shutterstock

American Airlines Flight 1632 was conducting a normal landing as it approached Dallas following its three-hour and 30-minute flight from Washington, DC. While flight data revealed that both the autobrake system and ground spoilers were functional as the aircraft touched down, pilots soon recognized that the brakes were not working properly.

During its initial touchdown, the autobrake parameter changed from ‘No Auto Brake’ to ‘Auto Brake Applied,’ but switched back to ‘No Auto Brake’. Pilots then engaged manual braking, but found the aircraft was not decelerating effectively. At around 1,000ft from the runway end, the flight crew radioed air traffic control (ATC), indicating a “total brake failure” and called for emergency services.

Passengers exited the aircraft via airstairs and were bussed to the terminal, with no injuries reported among passengers or crew. The aircraft was then towed to the apron for inspection and was returned to service nine days later.