South Korean investigators said on Saturday they were close to finalising the transcript of the cockpit voice recorder from a fatal plane crash that left 179 people dead last week.

The recording may hold clues to the final moments of Jeju Air flight 2216, which was carrying 181 passengers and crew from Thailand to South Korea on Sunday when it belly-landed before slamming into a concrete barrier at the end of an airport runway.

South Korean and US investigators, including from the aircraft’s manufacturer Boeing, have been combing the crash site in southwestern Muan since the disaster to establish a cause.

“The transcript of the cockpit voice recorder (CVR) is expected to be completed today, and the flight data recorder (FDR) is in the process of being prepared for transport to the United States” for analysis, South Korea’s land ministry said in a statement.

Investigators also recovered the aircraft engine from the crash site this week, the ministry added.

The exact cause of the Boeing 737-800 crash is still unknown, but investigators have pointed to a bird strike, faulty landing gear and the runway barrier as possible issues.

Authorities this week carried out search and seizure operations at Muan airport where the flight crashed, a regional aviation office in the southwestern city, and Jeju Air’s office in the capital Seoul, police said.

Jeju Air’s chief executive Kim E-bae has been banned from leaving the country as the investigation continues, police also said.

The pilot warned of a bird strike before pulling out of a first landing and then crashing on a second attempt when the landing gear did not emerge.

Dramatic video showed the plane colliding with the concrete barrier at the end of the runway before bursting into flames.

Authorities have begun lifting the wreckage of the jet and returning some of the identified victims’ bodies and personal belongings recovered from the crash site to grieving families.

The plane was largely carrying South Korean holidaymakers back from year-end trips to Bangkok, except for two Thai passengers.

Images from local media showed authorities handing over items, including smartphones and dried mango and coconut sourced from Thailand.