SEOUL, South Korea — The black boxes from the Jeju Air plane that crashed in South Korea on Sunday are the center of focus as a joint team of U.S. and South Korean investigators work to determine the cause of the deadliest aviation disaster of 2024.

Data from the two black boxes, the flight data recorder and the cockpit voice recorder, will be instrumental in determining what happened in the minutes before the Boeing 737-800 crash-landed at Muan International Airport in the country’s…