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

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.

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

Exact cause of crash remains unclear but preliminary report suggests a combination of factors contributed to incident

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.

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 to determine what caused the deadliest air disaster on South Korean soil.

The South Korean authorities have released a preliminary report concerning the Jeju Air accident. The incident on December 29, categorized as the most lethal aviation incident for South Korea, is still under investigation,