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,

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

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. The Korea JoongAng Daily said Sunday that the families of the victims agreed to end the investigation after authorities disclosed details about bird strikes linked to the crash.

South Korea released on Monday a preliminary report on its investigation into a Jeju Air crash on Dec. 29 at Muan International Airport that killed 179 people in the deadliest air disaster on the country's soil.

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.

South Korea has handed in its initial report into the country's deadliest plane crash. Jeju Air flight 2216 exploded last month after an emergency landing. Nearly 180 people were killed, with only two survivors.

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