FAA issues Boeing 737 AD for incorrectly installed MLG hoses following American Airlines runway excursion
The FAA's directive should only affect around 100 Boeing 737 Next Generation (NG) aircraft in the United States.
Following an American Airlines Boeing 737-800 runway excursion, and the National Transportation Safety Board (NTSB) publishing its final report about the incident, the Federal Aviation Administration (FAA) has now issued an airworthiness directive (AD) to address the potential issue that was determined to be the probable cause of the safety event in February 2024.
On November 21, 2025, the FAA filed the AD, skipping the usual publishing process that involves gathering comments from stakeholders with a notice of proposed rulemaking (NPRM), warning that incorrectly connected main landing gear (MLG) hydraulic hoses “could result in incorrect antiskid system operation, which could result in loss of braking and potential for a runway excursion with serious or fatal injuries.”
“The FAA has received a report of a runway excursion caused by loss of braking. An inspection found that the right MLG hydraulic hoses for the brakes were incorrectly installed (crossed) at the flow limiters, and the left MLG wheel speed transducer wires were interchanged.”
The directive, which will be published on November 25 and will affect 737-700, 737-800, 737-900, and 737-900ER aircraft, should only result in immediate inspections of around 100 737s registered in the United States, the FAA said. That was despite the fact that Boeing’s Requirements Bulletin (RB) 737-32A1599 included 6,816 737s that could undergo inspections to ensure correctly installed MLG hydraulic hoses.
To comply with the directive, operators will have to conduct a general visual inspection (GVI) of the left and right MLG brake hydraulic hoses for any crossed ones, conduct antiskid valve and transducer operational tests, and take corrective actions if needed.
The FAA estimated that the GVI and operational tests of the antiskid valve and transducer should take mechanics around seven work hours, which are valued at $85, resulting in the inspection and tests costing operators $595 per aircraft.
According to the regulator, it did not publish an NPRM and just issued the final directive since an “unsafe condition exists that requires the immediate adoption of this AD without providing an opportunity for public comments prior to adoption.”
“The FAA has found that the risk to the flying public justifies forgoing notice and comment prior to adoption of this rule, because incorrectly installed (crossed) brake hydraulic hoses for the MLG and interchanged left MLG wheel speed transducer wires could cause incorrect antiskid system operation and result in loss of braking and a runway excursion with serious or fatal injuries.”
In addition, the crossed hydraulic hoses could remain unnoticed until an aircraft experiences degraded braking performance, and the “compliance time in this AD is shorter than the time necessary for the public to comment and for publication of the final rule.”
As such, the typical directive publishing process, which includes potential comments from the public, was found to be “impracticable,” the FAA stated.
It filed the directive less than two weeks after the NTSB published its final report about a runway excursion of an American Airlines 737-800, registered as N991AN, at Dallas/Fort Worth International Airport (DFW) in February 2024.
The incident had not resulted in any serious injuries to the passengers or the crew who were on board the aircraft.
In its final report, the NTSB concluded that the probable cause of the incident was “improper maintenance due to human error during a braking system modification diminished braking performance.”
“[…] the lack of a functional check to verify the flexible hydraulic hoses and transducer wiring were connected correctly after the braking system modification” also contributed to the runway excursion, the NTSB added.
After the event, American Airlines and Boeing had made revisions to their documents to ensure that no aircraft had crossed hydraulic hoses, with the airline ordering the inspection of its 737 fleet for swapped transducer wiring, resulting in 303 aircraft being examined. None had swapped transducer wiring, according to the investigators.
Rytis Beresnevicius
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