SEOUL: Bird feathers and bloodstains were found in both engines of the Jeju Airplane that crashed in December, killing 179 people, according to a preliminary investigation released Monday.

The Boeing 737-800 was flying from Thailand to Muan in southwest South Korea on December 29, carrying 181 passengers and crew, when it belly-landed and exploded into a fireball after slamming into a concrete barrier.

It was the worst aviation disaster on South Korean soil. South Korean and American investigators are still probing the cause of the crash, with a bird strike, faulty landing gear and the runway barrier being examined as possible issues.

Both engines recovered from the crash site were inspected, and bird bloodstains and feathers were “found on each”, the report said.

“The pilots identified a group of birds while approaching runway 01, and a security camera filmed HL8088 coming close to a group of birds during a go-around,” the report added, referring to the jet’s registration number.

It did not specify whether the engines had stopped working in the moments leading up to the crash.

DNA analysis identified the feathers and blood as coming from Baikal teals, migratory birds which fly to Korea in winter from their breeding grounds in Siberia.

The report also confirmed that both the cockpit voice recorder and flight data recorder had stopped working four minutes before the disaster, leaving a gap in the data.

It did not suggest a cause for the malfunction.

The captain had over 6,800 flight hours, while the first officer had 1,650 hours, the report said. Both were killed in the crash, which was survived only by two flight attendants.

The Jeju plane exploded in flames when it collided with a concrete embankment during its landing, prompting questions about why that type barricade was in place at the end of the runway.

Last week, authorities said they would replace such concrete barriers at airports nationwide with “breakable structures”.