Pilots’ actions after the bird strike are an early focus of the investigation, according to people familiar with the probe.

By Jack Kim 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.

A preliminary accident report into South Korea’s deadliest air disaster was submitted to the United Nations’ aviation agency on Monday.

The investigation into the deadliest air disaster on the country's soil remains ongoing, focusing on the role of bird strike and involving an analysis of the engines and the "localizer" landing guidance structure.

South Korean authorities have submitted a preliminary report on last month's fatal Jeju Air crash to the International Civil Aviation Organization. The ongoing investigation focuses on a 'bird impact' as well as examining the aircraft's engines and landing systems.

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The nation’s transport ministry reviewed structures near airport runways after the deadly crash of a Jeju Air flight late last month.

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.