AAIB Issues Safety Warnings for Leonardo AW139 Tail Rotors

The UK's Air Accidents Investigation Branch (AAIB) has issued three formal safety recommendations regarding the failure of the tail rotor duplex bearing (TRDB) on Leonardo AW139 helicopters. This regulatory action follows a June 2022 incident involving a Bristow Group-operated AW139, registration G-CIMU, which experienced a significant mechanical failure discovered during a post-flight maintenance inspection. The investigation, published on May 21, 2026, details how the component had degraded to the point of exposing internal ball bearings and releasing large amounts of carbon dust, creating an imminent risk of a total loss of tail rotor control.

Background and Regulatory Context

The AAIB investigation highlights that the AW139's bearing is classified as a critical part. Its failure mechanism is notably similar to the catastrophic 2018 crash of a Leonardo AW169 in Leicester, which resulted in five fatalities. In that 2018 event, the failure of a nearly identical tail rotor system led to a total loss of control. The AAIB reports suggest that the recurring nature of these failures has prompted a shift in how regulators view the certification of critical rotorcraft assemblies.

Following the identification of these risks, the European Union Aviation Safety Agency (EASA) issued AD 2022-0182-E, which mandated that the AW139 tail rotor duplex bearing must be discarded after accumulating 2,400 flight hours. The Federal Aviation Administration (FAA) subsequently adopted these requirements through AD 2023-03-03, legally enforcing repetitive inspections for the global fleet. These EASA Airworthiness Directives represent a broader industry move away from condition-based maintenance toward rigid, time-limited replacement intervals for flight-critical components.

Stakeholder Impact and Alternative Perspectives

The impact of these directives is significant for operators and manufacturers alike. For offshore helicopter operators like Bristow, the mandate introduces mandatory downtime and increased maintenance costs to comply with the 2,400-hour limit. Meanwhile, Leonardo Helicopters faces ongoing regulatory pressure to refine the tail rotor control mechanisms across its medium-sized helicopter family. According to FAA regulatory filings, these requirements are essential to maintaining the airworthiness of the platform.

Legal representatives for the victims of the 2018 Leicester crash have argued that the failure was an inherent design flaw that could have been addressed through earlier engineering modifications. Conversely, Leonardo maintains that the aircraft met all existing CS 29 (Certification Specifications for Large Rotorcraft) standards at the time of certification, suggesting that the industry should focus on updating certification frameworks rather than assigning individual negligence.

Technical Analysis

The investigation into G-CIMU indicates a trajectory toward stricter oversight of rotorcraft critical parts. Historically, the 2018 Leicester incident served as a catalyst for design reviews, and the recent AW139 findings confirm that the underlying mechanical vulnerabilities were not isolated to the AW169. This development signals that manufacturers will likely face more stringent requirements for redundant failure paths in tail rotor systems. The transition to hard-life limits underscores a regulatory preference for deterministic safety measures over complex, condition-based monitoring, which has proven difficult to execute reliably in high-vibration environments.

What Comes Next

Implementation of the AAIB's latest safety recommendations is expected to continue through late 2026. EASA and Leonardo are collaborating on long-term design assessments to ensure that the tail rotor architecture complies with evolving safety standards. Operators should expect continued emphasis on the 2,400-flight-hour discard limit and potentially expanded inspection requirements as the investigation findings are integrated into future maintenance manuals.

Why This Matters

This incident underscores the critical importance of component life-cycle management in maintaining fleet-wide safety. For aviation professionals, the shift toward mandatory replacement intervals signifies a move toward more conservative maintenance cycles, which effectively reduces the risk of in-flight mechanical failures but increases operational overhead for major rotorcraft operators.