The flight data recorder from the Sriwijaya Air aircraft that crashed last month, killing 62 people, showed problems with the autothrottle system that automatically controls engine power, Indonesia's air accident investigator said on Wednesday.

When the Boeing 737-500 jet reached the height of 8,150 feet (2,484 m) after take-off, the left throttle lever moved back while the right lever stayed in its original position, National Transportation Safety Committee (KNKT) investigator Nurcayho Utomo said.

The plane eventually rolled and then dived into the Java Sea, he said.

"What we know is the left autothrottle moved backward," Utomo told reporters. "We don't know if it's broken or not, but it's an anomaly because the left moved far back, the right did not as though it was stuck."

(With input from Reuters)