What happened
On 12 May 2022, an Agusta A109E helicopter, registration VT-CHG, was conducting a night route check flight at Raipur Airport. The crew, consisting of a pilot in command and a co-pilot, departed from the airport's police line helipad. Approximately ten minutes into the flight, the crew identified a significant reduction in rudder effectiveness and notified Air Traffic Control (ATC) of their intention to return to the airport due to a technical issue.
During the return, the crew performed several low passes over runway 24. While attempting to land, the aircraft touched down on the runway but continued to roll for approximately 13 seconds. Following this, the helicopter lifted off again and began a sharp yaw to the right. The aircraft entered an uncontrolled clockwise spin, climbing to roughly 1,680 feet before descending and crashing near taxiway A. The impact resulted in two fatalities and the total destruction of the helicopter.
The investigation
AAIB India investigators performed an extensive examination of the wreckage and flight data. Analysis of the Digital Flight Data Recorder (DFDR) and Cockpit Voice and Data Recorder (CVDR) revealed that the aircraft experienced uncommanded attitude changes and low-frequency oscillations just prior to the loss of control. Laboratory examinations focused on the tail rotor assembly and critical fastening components.
Technical scrutiny of the support bearing sleeve assembly and the outboard locking nut was conducted using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The investigation examined the condition of the duplex bearing, the presence of thread-locking adhesive, and the integrity of the chromate conversion treatment on the aluminum alloy components.
Findings
- The investigation established that the accident was caused by a mechanical failure in the tail rotor assembly.
- Microscopic analysis revealed that the outboard locking nut had unscrewed, leading to contact between the nut and the support bearing sleeve assembly.
- Significant damage, including deep nicks and circumferential marks, was found on the support bearing sleeve assembly's inner surface and threads.
- The duplex bearing was found to be in a state of failure, with the outer rings separated from the inner rings.
- Evidence of generalized oxidation and the absence of required chromate conversion treatments were noted on several components.