Investigators say they have found evidence that a bird strike killed 179 people on a passenger plane that crashed in South Korea in December.

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

The investigation into the crash – the deadliest on South Korean soil – is now focusing on the role of bird strikes and a concrete structure at the end of the runway where the plane crashed.

The Boeing 737-800 engines were removed and the concrete structure was further inspected, the report said.

The Jeju Air flight from Bangkok took off on the morning of December 29 and was flying to Muan International Airport in the southwest of the country.

At around 08:57 local time, three minutes after the pilots made contact with the airport, the control tower advised the crew to be cautious of “bird activity”.

At 08:59, the pilot reported that the plane had hit a bird and declared a May Day signal.

The pilot then requested permission to land from the opposite direction, during which it landed without deploying its landing gear. It overshot the runway, hit the concrete structure and then exploded, the report said.

Authorities previously said the plane’s flight data and cockpit voice recorders stopped recording about four minutes before the disaster.

Experts who flew the same type of aircraft involved in the crash have also questioned the presence of concrete barriers along the runway – some suggesting that the number of casualties would have been lower if they had not been there.

The concrete structure houses a navigation system that assists aircraft during landing, known as a localizer.

South Korea’s transport ministry has said the system could be found at other airports in the country and even overseas.

Last week, authorities announced that concrete barriers used for navigation at seven airports across the country would be replaced. Runway safety areas at seven airports will also be adapted after a review.

The preliminary report has been submitted to the UN aviation agency and authorities in the United States, France and Thailand.