Preliminary investigation report of helicopter crash inconclusive as flight data recorder had been removed

Final accident investigation report could take up to a year

The Ministry of Infrastructure and Transport (MoIT) released a preliminary accident investigation report of the helicopter crash that occurred on 3 March 2023 killing a woman and her daughter. According to the report, the cause and contributing factors of the accident have not been determined.

After the accident, a team of aircraft accident investigators was formed on 8 March 2023, as per the existing Civil Aviation Act of Bhutan 2016, mandated under section 117 of the Act to investigate the Drukair helicopter (A5-BHT) accident at Wachey, Lunana, on 3 March 2023, by the MoIT.

Through the preliminary investigation report, it was found out that the weather during the day of the accident was fine, as the locals reported, with no winds on the day of the accident, and the weather en route to Wachey was acceptable, with high clouds, broken or scattered clouds, and suitable wind conditions according to the pilot.

Similarly, the National Centre for Hydrology and Meteorology (NCHM) forecast partly cloudy weather for Gasa, therefore, NCHM did not issue a weather warning alert.

It was reported that the pilot had good visibility during the approach to Wachey.

The preliminary investigation report stated this kind of helicopter is normally equipped with the Vision 1000 flight data recorder. The Vision 1000 collects inertial and positioning data, ambient acoustic data, and cockpit imagery, which are stored on a crash-hardened memory module as well as a removable secure digital card.

This flight data recorder, is critical in supporting accident investigations because it provides investigators with a virtual bird’s-eye view of what happened. However, during the crash, it was not present on board on the day of the accident because it had been removed for maintenance (removed on 1 March 2023, declared inoperative under MEL category D).

Likewise, it was found out that the flight tracker (VR) device, which tracks and records the flight path every 15 seconds, also failed to record two minutes before the crash.

An official from the Aircraft Accident Investigation Team said that the investigation is not complete and this is just a preliminary investigation, which is more about getting factual information to set a way forward.

Under the examination and read-out section of the report, it was found that the wreckage contained critical equipment, such as the engine data receiver, vehicle and engine multifunction display, engine control unit, and V2-track. It is sent to the French Bureau of Enquiry and Analysis (BEA) for examination and reading out.

The report highlighted the results will be in the final report.

The official said, “After sending these four components to the manufacturers in France, after having the readouts and all, we will start analyzing the findings, probable causes, and contributing factors.”

“It is just a preliminary report, and we cannot ascertain a cause; as only after a final investigation report can we determine the cause and contributing factors,” he added.

The official clarified that this report does not determine who is accountable or responsible for the accident right now.

It was said that the final investigation report could take up to a year, which is according to the standards.

Although the Aircraft Accident Investigation Team has recommended that Drukair Helicopter Services immediately ground the pilot who was involved in the accident from flying until further notice, however, the official said, “It is just that he can no longer fly domestically or internationally until further notice, and it is not about the pilot’s fault.”

The preliminary report provides factual information established in the early phase of the investigation, and has been prepared to provide timely information. Preliminary reports contain no analysis or findings, which will be detailed in the investigation’s final report.

The team is still proceeding with the investigation. The information in the preliminary report is subject to change as the investigation progresses.

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