The South Korea-led investigation into December's fatal Jeju Air crash, which caused over 179 deaths, says that the pilots turned off the less-damaged left engine after a bird strike.

What Happened: "The investigation team has clear evidence and backup data, so its finding will not change," a source said, cited by Reuters in its report on Monday.

The evidence, including a physical engine switch, cockpit voice recorder, as well as computer data, shows that the pilots turned off the left engine instead of the right engine after the bird strike as part of emergency safety protocols, the report said.

The investigators briefed the families of the victims on Saturday and planned to release a preliminary report, but were met with objections by the victims' families.

The lawyers representing the families claimed that their clients feel the report "appeared to apportion blame to the pilots without exploring other contributing factors," the report said.

The representatives of the victims' families, as well as the Jeju Air pilots' union, have also said that the embankments at the Muan airport also need to be investigated, which experts believe could have contributed to the higher death toll, the report says.

The pilots' union also accused investigators of trying to make the pilots "scapegoats" by saying that there was minimal damage to the left engine, when both engines showcased bird remains, the union said.

Why It Matters: The report comes as air crash reports involving Boeing Co. (NYSE:BA) Aircraft have been in the news lately. South Korean authorities ordered all airlines in the country to conduct checks on the fuel switches on Boeing Aircraft in the country.

This comes in despite the FAA and Boeing saying that the fuel switch locks on Boeing aircraft were safe, as reports emerged that fuel supply to the engine on board the Boeing 787-Dreamliner was abruptly cut off in the moments leading up to last month's fatal crash in the Indian city of Ahmedabad.

Elsewhere, U.S. Transportation Secretary Sean Duffy said that the Trump administration would require an additional $19 billion to overhaul the aging Air Traffic Control system in the U.S.

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