The Federal Aviation Administration issued a final rule on November 5, 2025, adopting a new airworthiness directive for certain MHI RJ Aviation ULC airplanes, including models CL-600-2C10, CL-600-2C11, CL-600-2D15, CL-600-2D24, and CL-600-2E25. This directive, effective November 20, 2025, addresses reports of loose and missing bolts on the horizontal stabilizer anti-yaw steady fitting block. Prompted by findings during routine maintenance, the rule requires repetitive torque checks to prevent potential loss of the stabilizer, which could lead to loss of aircraft control, especially under additional stresses like bird strikes or gust loading. The action stems from a Transport Canada mandate and highlights ongoing efforts to ensure safety in regional jet operations across North America.
Background and Origins of the Directive
The issue originated from a maintenance inspection on a horizontal stabilizer, where technicians discovered a missing bolt from the anti-yaw steady fitting block, with the bolt and hardware found on nearby structure. Additional bolts in the same assembly were loose. These bolts lack a secondary locking feature, increasing vulnerability over time. Transport Canada, as the state of design authority, issued AD CF-2025-38 on August 19, 2025, to address this condition. The FAA, under its bilateral agreement with Transport Canada, reviewed the matter and determined the unsafe condition could affect U.S.-registered aircraft. This AD applies to 597 airplanes in the U.S. registry, primarily regional jets used in commercial aviation.
Key players include the FAA's Operational Safety Branch, Transport Canada National Aircraft Certification, and MHI RJ Aviation ULC, the current type certificate holder formerly held by Bombardier, Inc. The directive reflects standard FAA procedures for adopting foreign airworthiness directives when risks extend to U.S. operations, as outlined in 14 CFR Part 39.
The Unsafe Condition Explained
The anti-yaw steady fitting block is a critical component of the horizontal stabilizer, which maintains aircraft stability and control during flight. Loose or missing bolts here compromise structural integrity. According to the FAA, such failures, when combined with external factors like bird strikes or sudden gusts, could result in the loss of the horizontal stabilizer. This scenario might lead to catastrophic loss of control, endangering passengers, crew, and ground safety.
The MCAI from Transport Canada describes the risk in detail, noting that the bolts' design without secondary locking allows for gradual loosening due to vibration or operational stresses. No specific incidents of in-flight failures are cited, but the potential for escalation justifies immediate action. This aligns with broader aviation safety principles, where preventive measures address latent defects before they manifest in accidents.
Requirements and Compliance Details
The AD mandates repetitive torque checks of the four attachment bolts on the horizontal stabilizer anti-yaw steady fitting block. Operators must inspect tightening torque, replace any loose or missing bolts and nuts, and then torque all bolts to specified levels. Initial checks are required within timelines based on aircraft flight hours, with repeats every 2,200 flight hours thereafter.
An optional terminating action involves replacing the hardware, including measuring hole diameters, reaming if necessary, and installing new bolts, nuts, washers, and cotter pins to create a double safety mechanism. This replacement, detailed in Transport Canada AD CF-2025-38, would eliminate the need for ongoing inspections. The FAA estimates costs for the required checks at up to $510 per aircraft per cycle, with the optional replacement at $622 per aircraft.
Differences from the Canadian directive include adjusted compliance phrasing, such as using 'flight hours' instead of 'hours air time' and allowing the replacement as optional rather than mandatory. The FAA is considering mandating the replacement in a future rule, pending public comments.
Legal and Regulatory Context
This AD fits into a framework of U.S. aviation regulations under Title 49, Subtitle VII, which empowers the FAA to issue rules promoting safe flight. It draws from precedents like previous ADs on Bombardier regional jets, such as those addressing stabilizer trim issues or elevator control problems (e.g., AD 2019-03-15). Politically, the directive underscores bipartisan emphasis on aviation safety, with agencies like the Department of Transportation prioritizing risk mitigation amid growing air traffic.
Perspectives vary. Manufacturers and operators may view the repetitive checks as burdensome, potentially increasing maintenance downtime and costs. Safety advocates, including groups like the Air Line Pilots Association, support such measures to prevent rare but severe failures. Regulators balance these by incorporating feedback periods, though this AD was issued without prior notice due to the urgent safety risk, invoking 'good cause' under the Administrative Procedure Act.
Potential Implications
In the short term, the AD ensures immediate risk reduction through inspections, likely preventing any incidents related to this defect. Operators face logistical challenges in scheduling checks without disrupting service, particularly for regional carriers reliant on these jets.
Long-term, the directive could influence design standards for future aircraft, emphasizing redundant locking features in critical assemblies. It may also prompt broader reviews of similar components across other models. Economically, compliance costs for the U.S. fleet could reach $304,470 per inspection cycle, though the optional replacement offers a cost-effective resolution. From a global standpoint, harmonization with Transport Canada strengthens international aviation safety cooperation.
Different viewpoints highlight trade-offs. Airlines might argue for extended compliance times to minimize operational impacts, while passengers and regulators prioritize uncompromised safety. No endorsement of any side is implied, but the AD's structure allows flexibility via alternative methods of compliance.
The directive represents a proactive step in aviation safety, addressing a specific mechanical vulnerability in MHI RJ regional jets. Key takeaways include the emphasis on repetitive maintenance to avert potential disasters and the option for permanent fixes. Looking ahead, operators may pursue the hardware replacement to streamline compliance, while the FAA could mandate it following comment periods. Ongoing debates may center on balancing safety mandates with operational efficiency, potentially shaping future regulatory approaches in aircraft maintenance.