The Federal Aviation Administration has ordered inspections, and in many cases a pump replacement, on 334 U.S.-registered Boeing 777s after one of the jets caught fire in a piece of landing-gear hardware. Airworthiness Directive 2026-19-04, published as a final rule on Sept. 28, traces the danger to a single missing lock washer and nut inside an electrical unit that let a hydraulic pump run hot enough to ignite. The agency says the order follows an in-service fire report, and its own investigation found the same failure could recur across hundreds of jets still flying with the same part.
A Missing Lock Washer Led to a Wheel-Well Fire
Investigators trace the ignition point to the alternating current motor pump, or ACMP, that helps move the 777’s main landing gear in and out of the fuselage. According to the FAA’s background section, a lock washer and nut were missing from a moving contact inside the pump’s electrical load control unit, letting continuous two-phase power reach the motor instead of shutting it off the way the design intended. Left unaddressed, the agency warned, the defect risks “ACMP overheating and igniting a fire in the wheel well and consequent damage to the airplane, loss of continued safe flight and landing and/or personnel injury.”
The risk was not hypothetical. The FAA’s directive states the rulemaking was “prompted by a report from an operator of a fire in the MLG wheel well on a Model 777 airplane” — the in-service event that sent Boeing back into the hardware and ultimately produced the fleet-wide order. Main landing-gear bays are not built with the dedicated fire-detection and suppression hardware that protects a 777’s engines or cargo hold, so a fault that starts there can smolder longer before a crew or ground crew notices it.
The rule covers 777-200, -200LR, -300 and -300ER passenger variants as well as the 777F freighter, meaning both passenger carriers and cargo operators fly jets exposed to the same wiring defect. The FAA’s tally of 334 U.S.-registered airplanes includes 290 that need an actual records check or physical inspection for a pump carrying part number 731966; the rest fall under the rule’s broader, permanent ban on ever installing that part number again. Airlines outside the United States flying the same 777 variants are not covered by this specific order, since FAA airworthiness directives apply only to U.S.-registered aircraft, though foreign regulators often mirror FAA action on shared Boeing designs.
The Fix for 334 Jets: Replace the Pump Within 60 Months
Any ACMP found with part number 731966 must be swapped for an approved replacement — part 3033115-100, or alternates 66133-06 and 66068-08 — and installing the original part on a 777 is now barred outright, effective the moment the rule takes hold on Nov. 2. Mechanics carrying out the work will follow the inspection and replacement steps Boeing spelled out in the service bulletin the FAA incorporated by reference into the rule, rather than inventing their own procedure airplane by airplane.
The FAA put a price on the work: about $170 per airplane for the records check or inspection alone, or roughly $49,300 across the affected U.S. fleet. Should a pump actually need replacing, the agency’s estimate climbs sharply, to as much as $77,099 per aircraft, though it notes some of that expense may ultimately be absorbed under manufacturer warranty rather than billed directly to the airline.
Operators have five years, until November 2031, to finish the work.
From a November Proposal to a Signed Final Rule
The fix did not arrive overnight. The FAA first floated it as a proposed rule in a Nov. 17, 2025 notice tied to docket FAA-2025-3997, giving airlines, mechanics and the public until Jan. 2, 2026 to comment before anything became binding. Roughly ten months later, the agency converted that proposal into the enforceable order covering the same 334-jet fleet.
The FAA’s authority for the order comes from 14 CFR Part 39, the federal framework that lets the agency compel a fix on any aircraft, engine or propeller once it confirms an unsafe condition, a process it lays out on its own page explaining how airworthiness directives work. This particular order was signed by Brian Knaup, acting deputy director of the FAA’s Integrated Certificate Management Division within the Aircraft Certification Service, on Sept. 16, twelve days ahead of formal publication in the Federal Register.
The Electrical Unit Behind the Overheating
The part at fault, the electrical load control unit, is supposed to cut power to the landing-gear pump once its job is done, preventing exactly the kind of sustained heat buildup investigators found. Without the missing lock washer and nut holding a moving contact in place, the unit instead kept delivering two-phase power continuously, turning a routine landing-gear actuation into a slow-building fire risk hidden inside the wheel well.
The 777 remains one of Boeing’s most widely flown long-haul jets, and nothing in the final rule grounds any of the 334 aircraft while the work gets done. Inspections, and pump swaps where needed, are due on a rolling schedule that runs through November 2031, tracked against the 290 airplanes the FAA says currently carry the flagged part.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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