Federal investigators have cited improper brake maintenance as a factor related to a 10 February runway overrun involving an American Airlines Boeing 737-800 at Dallas Fort Worth International airport.

After touching down, the 737’s auto-brake system failed, forcing the pilots to apply maximum manual braking, but not in time to keep the jet from exiting the runway threshold, according to a preliminary National Transportation Safety Board (NTSB) report released on 21 March.

American flight 1632 DFW runway overrun NTSB preliminary report 032124

Source: National Transportation Safety Board

“American 1632, total brake failure. We are departing the end of runway 17L. Roll crash fire rescue,” the jet’s captain radioed the airport tower as he tried to slow the aircraft after landing, says the report.

The 737 stopped on the paved “overrun” area of the runway. None of the 98 passengers and six crew aboard suffered injuries.

The incident involved American flight 1632 from Ronald Reagan Washington National airport.

“The safety of our customers and team members is our top priority and we are fully cooperating with the National Transportation Safety Board in its investigation,” American says.

The inquiry remains ongoing, but the NTSB report suggests workers improperly connected brake lines during maintenance on 6 February. The work was done by American as part of a project to replace steel brakes on the aircraft’s main landing gear with carbon brakes and wheel assemblies, as detailed in a 2016 Boeing service bulletin, the report says.

The job involved installing four “flow limiters” within hydraulic lines – two limiters for the left main landing gear and two for the right. On each side, one flow limiter is for the inboard brake and the other is for the outboard brake.

The NTSB notes that each flow limiter connects on one end to a flexible hydraulic line, and on the other end to a rigid hydraulic line. But on the right main landing gear, technicians apparently reconnected the two flexible lines to the wrong of the two flow limiters. The lines crossed when they should not have, meaning the line for the right inboard brake now mated with limiter for the right outboard brake, and vice-versa.

American flight 1632 DFW runway overrun NTSB preliminary report 032124

Source: National Transportation Safety Board

“The flexible hydraulic lines supplying pressure to the [right inboard] and [right outboard] brakes had been swapped at the connection with the flow limiters,” says the report.

The left main landing gear also had a problem involving an incorrectly installed wiring harness, the report adds. “The electrical connector for the [left outboard] and the [left inboard] wheel speed transducer were swapped.”