U.S. investigators, including representatives from the aircraft manufacturer, are examining the site of Sunday’s Jeju Air plane crash.

The crash, which claimed nearly all of the 181 lives on board, is South Korea’s deadliest air disaster in decades. Investigators are seeking to understand why the pilot attempted a landing after declaring an emergency.

According to the BBC, a pre-flight inspection revealed no mechanical problems.

The Guardian reported that investigators will analyze flight data, including speed, altitude, fuel levels, and cockpit voice recordings from the plane’s black boxes.

Air safety experts raised concerns on Tuesday about the proximity of an airport embankment to the runway’s end, as evidenced by video footage of the crash.

Reuters reported that comments in the airport’s operating manual, updated earlier in 2024, noted the embankment’s close proximity and recommended a location review during a planned expansion.

South Korea has initiated safety inspections of all 101 Boeing 737-800 aircraft in the country. The Transport Ministry stated that a five-day inspection, concluding Friday, will review maintenance and operational records.

The ministry confirmed that a team of eight U.S. investigators—one from the FAA, three from the NTSB, and four from Boeing—visited the crash site on Tuesday. Their findings are pending.

While a definitive cause may take months to determine, Muan fire station chief Lee Jeong-hyeon previously indicated that investigators are exploring various possibilities, including a potential bird strike.

Aviation consultant Mike Boyd commented on Sunday, “A bird strike on an engine might shut an engine down, but there’s so many redundant systems there, it just doesn’t make sense. We’re not in the dark, but we know the runway is 9,200 feet. It’s a very long runway. It [the plane] did come in hot and high, hot and fast. We don’t know why that was the real issue.”

The Associated Press and Reuters contributed to this report.