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,

South Korea released a preliminary report into last month’s deadly Jeju Air Co. crash that offers more detail on the role of bird strikes in the disaster, while still leaving crucial questions unanswered.

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

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Both engines of the Jeju Air plane that crashed last month contained duck remains, according to a preliminary report on Monday, with authorities still trying

Bird feathers and bloodstains were found in both engines of the Jeju Air plane that crashed in December, according to a preliminary investigation released on Monday. The Boeing 737-800 was flying from Thailand to Muan in South Korea on December 29 when it crash-landed and exploded into a fireball after slamming into a concrete barrier.

The first report on last month’s Jeju Air crash in South Korea 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.