FAA Proposes Airworthiness Directive for ATR 42 Turboprop Series

The Federal Aviation Administration (FAA) has issued a Notice of Proposed Rulemaking (NPRM) for a new Airworthiness Directive (AD) that would affect all ATR-GIE Avions de Transport Régional Model ATR42-200, -300, and -320 airplanes. The proposed safety regulation addresses a potential unsafe condition related to worn components in the aircraft's flap control system, which could lead to reduced control of the airplane.

This action was prompted by a report of worn splines on a flap asymmetry detector and its associated interconnection shaft. According to the FAA's notice, this wear could result in the loss of flap asymmetry monitoring. Such a failure would prevent the flight crew from being alerted to an asymmetrical flap condition, potentially leading to significant control difficulties during flap extension or retraction. The proposed directive aims to mandate inspections to identify and correct this issue before it can compromise flight safety.

Background of the Directive

The FAA's proposal is a direct response to mandatory safety information issued by a foreign civil aviation authority. The European Union Aviation Safety Agency (EASA), which is the primary certifying authority for the Franco-Italian built ATR aircraft, previously issued its own directive, EASA AD 2025-0087, to address the same safety concern. This EASA directive requires a special detailed inspection of the flap asymmetry detection mechanism for wear on the splines. The FAA's NPRM is intended to harmonize U.S. regulations with those of the EASA, a common practice that underscores the high degree of international cooperation in global aviation safety.

An Airworthiness Directive is a legally enforceable rule issued by the FAA to correct an unsafe condition found in a product, which can include aircraft, engines, propellers, or other components. The NPRM is the public notification step in this process, allowing stakeholders such as aircraft operators, maintenance organizations, and manufacturers to provide feedback on the proposed rule.

Technical Details and Safety Implications

The specific components at the center of the proposed AD are the splines on the flap asymmetry detector and the interconnection shaft. Splines are ridges or teeth on a drive shaft that mesh with grooves in a mating piece to transfer torque. Over time and with repeated use, these splines can wear down. In this case, significant wear could cause the connection to slip, rendering the asymmetry detection system ineffective.

Flaps are high-lift devices on the trailing edge of an aircraft's wings used during takeoff and landing. It is critical that they extend and retract symmetrically on both wings. An asymmetrical flap deployment can cause an uncommanded roll, creating a serious aircraft control problem, especially at low altitudes and speeds. The detection system is designed to immediately warn the crew of such a situation, allowing them to take corrective action. The failure of this monitoring system, as described in the Federal Register notice, would leave the flight crew unaware of a potentially hazardous control imbalance.

Affected Models and Regulatory Scrutiny

The proposed rule applies to all ATR 42 airplanes with model numbers -200, -300, and -320. These turboprop aircraft have been a mainstay of regional aviation for decades, with the first models entering service in the 1980s. Regulatory actions like this proposed AD are a normal part of the lifecycle for aging aircraft, as they address wear-and-tear issues that may only become apparent after many years and flight cycles. Proactive safety measures, based on in-service findings and analysis, are fundamental to maintaining the airworthiness of fleets worldwide.

Operators of the affected ATR 42 models in the United States will be required to comply with the final AD, which will likely mandate inspections and potential component replacements. While the FAA did not disclose the number of U.S.-registered aircraft affected, the rule would apply to any of these models currently on or imported into the U.S. registry.

What Comes Next

The FAA is inviting comments on this NPRM from the public and the aviation industry. All comments and supporting data must be received by the agency on or before April 13, 2026. After the comment period closes, the FAA will review the feedback and may issue a final rule, which could be identical to the proposal or incorporate changes based on the input received. Once a final rule is published, it will specify a compliance time for operators to complete the required inspections and any necessary corrective actions.

Why This Matters

This proposed directive highlights the continuous and collaborative nature of global aviation safety oversight. It demonstrates how a safety issue identified in one jurisdiction, through a directive from EASA, leads to harmonized regulatory action by the FAA. For operators, it underscores the importance of diligent maintenance and inspection programs, particularly for aging aircraft fleets. The action is a proactive measure designed to mitigate a potential risk before it results in an incident, reinforcing the data-driven approach that underpins modern aviation safety regulations.

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