The first report on last month’s Jeju Air crash in South Korea has confirmed traces of bird strikes in the plane’s engines, though officials haven’t determined the cause of the accident that killed all but two of the 181 people on board.

South Korea’s authorities investigating last month’s Jeju Air plane crash have submitted a preliminary accident report to the UN aviation agency and to the authorities of the United States, France and Thailand,

The exact cause of the Jeju Air crash remains unclear, and the investigation is complicated because the black boxes stopped recording four minutes before impact.

Authorities have suggested that migratory bird strikes were the cause of last month's deadly plane crash in South Korea, according to multiple reports.

Investigators have released a report that casts further light on the Jeju Air disaster that claimed the lives of 181 people on board, with only two people surviving the crash last month

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South Korean authorities concluded search and recovery operations and an investigation into the Dec. 29 crash of a Jeju Air plane that killed 179 people and found feathers and bloodstains in the two engines of the plane.

The report also said the plane's two black boxes — the flight data recorder and cockpit voice recorder — stopped recording about 4 minutes before the crash.