What happened
On 31 March 2003, a Bell 206B helicopter, registration EI-BHI, was conducting a routine Licence Proficiency Check (LPC) at Weston Airport, Co Kildare. The flight was being supervised by an authorized flight examiner to evaluate a qualified pilot. During a specific training maneuver designed to simulate a tail rotor failure, the aircraft made contact with the ground. While the landing was relatively mild and the crew experienced no injuries, the impact caused the rear portion of the right-hand skid to sever and break away from the aircraft.
The investigation
Following the incident, investigators performed a detailed metallurgical analysis of the fractured skid component. The examination revealed that the aluminum tube of the skid had suffered from severe exfoliation corrosion, particularly around the machined holes used for fixing plates. This corrosion had compromised more than 40% of the tube's circumference.
Further analysis by the skid manufacturer identified additional contributing factors, including galvanic corrosion caused by the contact of aluminum with steel components in a wet, saline-like environment, as well as stress-corrosion cracking. Evidence of mud within the tube suggested that moisture had penetrated the structure through existing cracks prior to the final failure.
Investigators also reviewed the aircraft's maintenance history. While a major service had been performed in November 2002, the specific, more stringent inspection requirements outlined in the manufacturer's updated Instructions for Continued Airworthiness (ICA) were not being utilized by the operator. Additionally, it was discovered that the change of aircraft ownership had not been communicated to the manufacturer, meaning the new owner had not been receiving updated maintenance documentation or service bulletins.
Findings
- The primary cause of the skid failure was advanced corrosion, specifically a combination of exfoliation, galvanic, and stress-corrosion cracking.
- The aluminum tube was significantly weakened by corrosion extending around 40% of its circumference.
- The failure was exacerbated by the lack of updated maintenance instructions, as the operator was unaware of the manufacturer's specific ICA requirements.
- A breakdown in communication regarding the change of aircraft ownership prevented the new owner from receiving essential safety updates and maintenance amendments from the manufacturer.
Safety action
Following the investigation, the AAIU issued safety recommendations to the Irish Aviation Authority (IAA). The IAA was advised to ensure that Bell 206 operators are aware of the necessity to perform skid tube inspections every 100 hours or six months, as specified by the manufacturer. Furthermore, the IAA was recommended to update the Certificate of Registration process to remind owners of their obligation to notify aircraft manufacturers of ownership changes to ensure the continuous supply of safety-critical documentation.