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’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 exact cause of the Jeju Air crash remains unclear, and the investigation is complicated because the black boxes stopped recording four minutes before impact.