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On Feb. 10 American Airlines flight 1632 on a Boeing 737-823 (N991AN) experienced a brake system anomaly after landing at Dallas Fort Worth International Airport (DFW), overrunning the runway. The post-incident examination revealed parts of the braking system were improperly reconnected after maintenance just days before the event.
The 737 left on a scheduled passenger flight from Ronald Reagan Washington National Airport (DCA) in Arlington, Virginia to DFW. The NTSB preliminary report stated the first officer was the pilot flying and the captain was the pilot monitoring. In a post-incident statement, the flight crew told investigators that an instrument landing system approach to runway 17L was flown with the plane configured with the flaps at 30 degrees and the auto brakes selected to three due to a reported tailwind of one knot. The crew said the approach and touchdown were normal and no directional control issues were reported. After touchdown the flight crew noted the AUTOBRAKE DISARM light illuminated and the brakes did not engage, requiring manual braking by applying pressure to the pedals while deploying the thrust reversers.
The flight crew said the plane began to decelerate with the thrust reversers at a slower pace. The FO said the brakes were not working correctly. On approach to taxiway Q7, the ground speed was higher than expected and the captain said, "My aircraft," to which FO responded, "Your aircraft." The FO called 60 knots and the captain did not notice any decrease in ground speed. The captain said he immediately moved both thrust reverser levers to the maximum reverse position. When the speed was about 40 to 50 knots and about 1,000 from the end of the runway the captain called the tower.
"American 1632, total brake failure, we are departing the end of runway 17L, roll crash fire rescue," the Captain said to the DFW tower.
The plane passed the runway threshold lights and the captain felt the plane come to a stop shortly after. The captain told passengers to remain seated and asked the FO to shut down the right engine and start the auxiliary power unit. After the APU was started, the left engine was shut down. The NTSB was notified of the event and began an incident investigation. Qualified parties involved include the FAA, American Airlines, The Boeing Company and Transport Workers Union - International Association of Machinists Association.
A preliminary data review showed that at touchdown the auto brake applied parameter momentarily (less than two seconds) transitioned from "No Auto Brk" to "Auto Brk" and then back to "No Auto Brk" for the remainder of the landing rollout. The left and right brake pressure increases to the maximum pressure, consistent with normal manual braking. The data also revealed the engine 1 and 2 thrust reverser parameters transitioned from "stowed" to "deployed" roughly eight seconds after touchdown. These remained deployed for about 12 seconds, were stowed for about six seconds then re-deployed for the remainder of the rollout.
ADS-B data showed that the left and right main landing gear touched down about 1,500 feet from the runway threshold and the nose landing gear came down after 2,000 feet. Groundspeed on the initial touchdown was 150 knots and 140 knots for the nose. The aircraft departed the end of the runway surface at 30 kts. Each main wheel has a brake unit bolted to a flange on the axle. On Feb. 6 AA completed a project to replace the existing MLG steel brakes on the incident 737 with carbon brakes and wheel assemblies per an engineering order based on the instructions in Boeing Service Bulletin 737-32-1429, revision 4, from Sept. 15, 2016.
With the modification to carbon brakes, four flow limiters replaced bulkhead unions, which were installed in to support fittings between the ridged hydraulic tube and a flexible hydraulic hose. To accommodate the increased length of the flow limiter the existing four rigid hydraulic tubes in the wing area inboard of each MLG were replaced with shorter rigid tubes. The installation of each flow limiter needed each flexible hydraulic hose to be temporarily disconnected from the existing bulkhead union. The bulkhead union was then replaced by a flow limiter and the flexible hose was then reconnected.
The post-incident troubleshooting and the inspection of the brake control system found the flexible hydraulic lines to the number three right inboard and number four right outboard MLG brakes were improperly reconnected after the carbon brake/flow limiter installation. The flexible hydraulic lines supplying pressure to the number three and four MLG brakes were swapped at the connection with the flow limiters. The system troubleshooting also found there was a discrepancy with the wiring to the left MLG wheel speed transducers. During a wheel speed transducer operational test, maintenance found the wiring harness in the left MLG axle had been installed incorrectly. The electrical connector for the number one left outboard and number two left inboard wheel speed transducer were swapped.
After the plane came to a stop at the end of the runway, the 104 passengers and crew deplaned without injury.