"Flight data and cockpit voice recorders from the South Korean passenger plane that crashed last month stopped recording four minutes before the disaster, the country's transport ministry has said.
The crash of the Jeju Air flight killed 179 people, making it the deadliest air accident on Korean soil. Two cabin crew members were the only survivors.
Investigators had hoped that data on the recorders would provide insights about the crucial moments before the tragedy.
The ministry said it would analyze what caused the "black boxes" to stop recording.
The recorders were originally examined in South Korea, the ministry said.
When the data was found to be missing, they were taken to the US and analyzed by American safety regulators.
The plane was traveling from Bangkok on 29 December when it crash-landed at Muan International Airport and slid into a wall off the end of the runway, bursting into flames.
Sim Jai-dong, a former transport ministry accident investigator, told Reuters news agency that the loss of data from the crucial final minutes was surprising and suggested that all power, including back-up, could have been cut.
They have also focused on why the Boeing 737-800 did not have its landing gear down when it hit the runway.