The two flight recorders on board a South Korean airliner stopped working before the jet crashed during an emergency landing and subsequent crash that killed 179 of the 181 people on board, officials said Saturday.

The missing data deepens the puzzle of what caused the deadly air disaster in Muan, South Korea, late last month.

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Ultimately, the plane crashed, killing 179 people in South Korea’s worst aviation disaster. A standard pre-flight inspection found “no issues” with the Jeju Air passenger plane before it crashed.

South Korea’s leading low-cost carrier, heavy with debt and its stock already near record lows, is now facing intense public and government scrutiny.

SEOUL (Reuters) -South Korea plans to improve the structures housing the antenna that guide landings at its airports this year following December's fatal crash of a Jeju Air plane, which skidded off the runway and burst into flames after hitting such a structure.

The two black boxes on the Boeing jet involved in the worst aviation disaster on South Korean soil stopped recording about four minutes before the accident, the transport ministry said on Saturday. South Korean investigators previously said the flight data and cockpit voice recorders were key to finding out the cause of last month's crash that killed 179 people.