Date:	Saturday 10 February 2024
Time:	19:42
Type:	Boeing 737-823 (WL)
Owner/operator:	American Airlines
Registration:	N991AN
MSN:	30920/2945
Year of manufacture:	2009
Fatalities:	Fatalities: 0 / Occupants: 104
Aircraft damage:	Minor
Category:	Incident
Location:	Dallas/Fort Worth International Airport (DFW/KDFW), Dallas, TX -   United States of America
Phase:	Landing
Nature:	Passenger - Scheduled
Departure airport:	Washington-Ronald Reagan National Airport, DC (DCA/KDCA)
Destination airport:	Dallas/Fort Worth International Airport, TX (DFW/KDFW)
Investigating agency:	NTSB
Confidence Rating:	Information verified through data from accident investigation authorities

Narrative:
On February 10, 2024, about 19:42 central standard time, American Airlines (AA) flight 1632, a Boeing 737-823, N991AN, experienced a brake system anomaly after landing on runway 17L at the Dallas Fort Worth International Airport (DFW), Dallas-Fort Worth, Texas. The airplane came to a stop beyond the south end of the runway threshold in the paved overrun area of the runway. The 104 passengers and crew deplaned via airstairs onto the overrun area with no injuries. The flight was operating under the provisions of Title 14 Code of Federal Regulations Part 121 as a scheduled domestic passenger flight from Ronald Reagan Washington National Airport (DCA), Arlington, Virginia to DFW.

The first officer (FO) was the pilot flying and the captain was the pilot monitoring. In a postincident statement, the flight crew reported that an instrument landing system (ILS) approach to runway 17L was flown with the airplane configured with the flaps at 30° and the autobrakes selected to 3 due to a reported tailwind of one knot. They stated that the approach and touchdown were normal with no directional control issues noted. Shortly after touchdown, the flight crew observed the AUTOBRAKE DISARM light illuminate and the brakes did not engage requiring manual braking by applying pressure to the pedals while deploying the thrust reversers.

The flight crew stated that the airplane began to decelerate with the thrust reversers but at a slower pace. The FO indicated that the brakes were not working correctly. When approaching taxiway Q7, the ground speed was higher than expected and the captain stated, “my aircraft” and the FO responded, “your aircraft.” The FO called 60 knots and the captain noticed no decrease in ground speed. The captain indicated that he immediately moved both thrust reverser levers to their 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 DFW tower, “American 1632, total brake failure, we are departing the end of runway 17L, roll crash fire rescue.” Passing the runway threshold lights, the captain felt the airplane come to a stop a short time later.

The captain made the “Remain Seated” passenger announcement and asked the FO to shut down the right engine and start the auxiliary power unit (APU). After the APU was started, the left engine was shut down.

The NTSB was notified of the event and an incident investigation was started. Qualified parties were invited to participate in the investigation. These included the Federal Aviation Administration (FAA), American Airlines, The Boeing Company, and the Transport Workers Union - International Association of Machinists (TWU-IAM) Association.

NTSB group chairs in the areas of systems, maintenance, and flight data and voice recorders were assigned.

Data from the digital flight data recorder (DFDR) was sent to the NTSB’s Vehicle Recorder Laboratory in Washington, DC, for analysis. A preliminary data review has been completed and a plot showing the braking parameters. Data showed that at touchdown the auto brake applied [Auto Brk Applied] parameter momentarily (less than 2 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 increased to their maximum pressure consistent with normal (manual) braking. Data also showed the engine 1 and 2 thrust reverser parameters [Eng1 and Eng2 TR Dply-DEU] transitioned from “stowed” to “deployed” about 8 seconds after touchdown. They remained deployed for about 12 seconds, were stowed for about 6 seconds, and then re-deployed for the remainder of the landing rollout.

The cockpit voice recorder (CVR) was removed from the airplane and sent to the NTSB’s Vehicle Recorder Laboratory in Washington, DC, for analysis.

Certified ADS-B data, which records more accurate latitude and longitude data than the DFDR, was provided to the NTSB by the FAA. Analysis of the ADS-B and DFDR data shows that the left and right main landing gear (MLG) touched down about 1,500 feet from the runway threshold and the nose landing gear came down just 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. The wheel and brake positions are identified as 1, 2, 3, and 4 defined as the left outboard position across the airplane to the right outboard position. On February 6, 2024, AA completed a project that replaced the existing MLG steel brakes on the incident airplane with carbon brakes and wheel assemblies per an engineering order based on the instructions contained in Boeing Service Bulletin 737-32-1429, revision 4, dated September 15, 2016.

As part of the modification to carbon brakes, flow limiters (total of 4), replaced bulkhead unions (total of 4), which were installed in support fittings between the ridged hydraulic tube and a flexible hydraulic hose. To accommodate the increased length of the flow limiter, the existing rigid hydraulic tubes (total of 4), in the wing area inboard of each MLG, had to be replaced with shorter rigid tubes. The installation of each flow limiter required 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 reconnected.

Post-incident troubleshooting and inspection of the brake control system found the flexible hydraulic lines going to the number 3 (right inboard) and number 4 (right outboard) MLG brakes had been improperly re-connected after the carbon brake/flow limiter installation. The flexible hydraulic lines supplying pressure to the number 3 and 4 MLG brakes had been swapped at the connection with the flow limiters.

System troubleshooting also found a discrepancy with the wiring to the left MLG wheel speed transducers. During a wheel speed transducer operational test, maintenance found the wiring harness, located in the left MLG axle, had been installed incorrectly. The electrical connector for the number 1 (left outboard) and the number 2 (left inboard) wheel speed transducer were swapped.

The investigation continues.

Weather about the inciden time (0142Z, 11 Feb.)
KDFW 102353Z 09005KT 10SM SCT017 BKN040 BKN090 OVC250 13/10 A2982 RMK AO2 SLP093 60001 T01330100 10139 20117 53003
KDFW 110104Z 06005KT 10SM OVC017 13/10 A2982 RMK AO2 T01280100
KDFW 110153Z 06008KT 10SM OVC015 12/10 A2983 RMK AO2 SLP099 T01220100
KDFW 110104Z 06005KT 10SM OVC017 13/10 A2982 RMK AO2 T01280100
KDFW 110153Z 06008KT 10SM OVC015 12/10 A2983 RMK AO2 SLP099 T01220100
KDFW 110253Z 06009KT 10SM OVC014 12/10 A2983 RMK AO2 SLP100 T01220100 51006

NTSB

https://twitter.com/FlyingHighRyan/status/1756570834657759717
https://www.flightradar24.com/data/aircraft/n991an#33f3340d
https://globe.adsbexchange.com/?icao=add667&lat=32.875&lon=-97.010&zoom=20.0&showTrace=2024-02-11&trackLabels

Figure: Photograph showing the swapped hydraulic lines on the right MLG (American Airlines photo via NTSB)

Date/time	Contributor	Updates
11-Feb-2024 10:41	ASN	Added
11-Feb-2024 10:42	ASN	Updated [Location]
11-Feb-2024 10:47	ASN	Updated [Date, Time, Aircraft type, Narrative]
11-Feb-2024 10:51	ASN	Updated [Narrative, Category]
12-Feb-2024 07:35	fairchildbrad	Updated [Total occupants, Narrative]
21-Mar-2024 19:28	Captain Adam	Updated [Time, Location, Source, Damage, Narrative, Category, Accident report, Photo]