FAA mandates inspections on 737 Max door straps and proposes 787 Trent 1000 engine fix

The Federal Aviation Administration (FAA) has stepped up oversight of Boeing aircraft by issuing new directives aimed at enhancing safety on the 737 Max and 787 Dreamliner fleets. This week, the agency mandated inspections on the Boeing 737 Max focusing on structural fasteners known as bear straps, which are located on the upper corners of the right-side forward doorframe. The inspections address potential cracking from stress that could jeopardize structural integrity.

Cracking issues with bear straps have a precedent on earlier 737 models, first identified more than a decade ago. After recognizing the problem on 737 Classics, the FAA mandated inspections in 2014. Boeing subsequently notified 737 Next Generation operators in 2019 and recommended inspections, which became mandatory by FAA rule in 2021. December 2024 saw Boeing issuing an Alert Requirements Bulletin to 737 Max operators outlining the need for fuselage skin and bear strap inspections, now formally required by the FAA's latest airworthiness directive (AD).

The FAA states that due to the design similarities between the 737 Max and its predecessors, there is a credible risk that Max variants could develop the same stress cracks in the bear straps as older aircraft. Stress concentration at door cutouts causes the fuselage skin and bear strap to undergo high operating stresses, leading to cracks that may compromise critical structural components. Boeing emphasized that these inspections serve as multiple opportunities to detect and address cracks before they reach critical lengths.

Alongside the 737 Max directive, the FAA also issued a proposed rule to address a specific safety risk involving Rolls-Royce Trent 1000 turbofan engines installed on Boeing 787 Dreamliners. The concern involves the potential for uncontained failures on the left-side Trent engine, which could cause debris to damage systems on the right-side engine. This scenario might trigger a dual engine failure with serious safety implications.

The agency’s notice cited a manufacturer report indicating insufficient coverage on the protection system of the left fan cowl of the right engine, allowing intermediate pressure turbine rotor debris to impact components such as oil lines or air-pressure sensors. Boeing responded in January with a Special Attention Requirements Bulletin advising 787 operators to inspect Trent engines and replace fan cowls on right-side engines to mitigate this hazard.

The FAA's proposed AD would make these inspections and fan cowl replacements mandatory, although it affects only a small number of aircraft — 22 787s registered in the US, as most American carriers use 787s equipped with GE Aerospace’s GEnx engines instead. This targeted regulatory approach focuses on the relatively limited fleet exposed to the issue.

Boeing noted ongoing efforts to analyze root causes and develop engineering changes to prevent such cracking in 737 Max bear straps going forward. The combination of directives reflects increased scrutiny on structural and engine-related risks following operational experience and safety feedback.

These FAA actions follow a history of proactive measures on similar issues: vulnerabilities discovered on former 737 variants have guided inspection regimes that the agency is now extending to newer models. The Trent 1000 engine focus highlights evolving understanding of engine failure scenarios and their cascade effects on twin-engine long-haul aircraft.

Ensuring the structural soundness of doorframe components and the reliability of engine protection systems is critical for passenger safety and fleet integrity. Operators of affected aircraft must comply with the FAA timelines for inspections and replacements to remain airworthy, reinforcing the agency's commitment to risk mitigation stemming from real-world operational data.