By Jack Kim and Lisa Barrington SEOUL (Reuters) -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.

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 feathers and blood stains on both engines of the Jeju Air plane were from the Baikal teal, a type of migratory duck that files in large flocks, according to a preliminary investigation report published on Monday.