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.

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

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.

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

The six-page report released by South Korean authorities a month after the crash said both engines of the Boeing 737-800 jet contained DNA from Baikal Teals, a type of migratory duck that flies to South Korea for winter in huge flocks.

Following the deadly Jeju Air accident, the government ordered low cost carriers to reduce flight times, boost pilot training and expand maintenance crews.

South Korea will extend runway safety areas and redesign infrastructure after the crash of a Jeju Air Co. flight last month that killed almost everyone on board, sparking criticism that the design of the airport might have exacerbated the accident.

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The South Korean Ministry of Transport announced that it will release a preliminary report on the Jeju Air plane crash by Monday. The accident claimed the lives of 179 people, with two miraculously surviving.