The South Korea-led investigation into Jeju Air's fatal plane crash in December has "clear evidence" that pilots shut off the less-damaged engine after a bird strike, a source with knowledge of the probe said on Monday.

In May, families of the victims lodged a criminal complaint against Jeju Air CEO Kim E-bae, citing professional negligence. Mr Kim is among 24 people being investigated by the police over their role in the accident.

Investigators have found that the pilots of the Jeju Air Boeing 737 that crashed in December, killing 179 people on board, seemed to have shut off the wrong engine that was damaged in a bird strike, according to reports.