South Korea’s transportation ministry launched an internal inspection Thursday into how it conducted its investigation into Korean Air’s “nut rage,” pressured by mounting criticism that it intended to acquit the airline and its troubled former vice president.

“We will thoroughly review all proceedings of the investigation to see if there were any flaws,” an official from the Ministry of Land, Infrastructure and Transport said, asking not to be identified.

The chief steward of a Dec. 5 Korean Air flight from New York to Incheon was forced off the plane by former Korean Air Lines Co. Vice president Cho Hyun-ah, who became outraged when she was served some nuts still in the package instead of on a plate. The plane, which was on the taxiway, returned to the gate so the steward could be removed.

Cho, 40, is the eldest daughter of the carrier’s chairman, Cho Yang-ho.

The ministry investigation had concluded that Cho raised her voice at the crew, but that the order for the chief steward to leave the plane had come from the flight’s captain.

However, the chief steward, Park Chang-jin, later came forward and said Cho had yelled at and pushed him and a flight attendant. Park also said he had been told to keep quiet about the incident. A senior official from the company was found to have sat in for about 20 minutes during the ministry’s questioning of Park, raising further suspicions of an attempted cover-up.

The transportation ministry announced Tuesday it would refer Cho’s case to the prosecution to investigate whether she violated the aviation safety law by causing a disturbance during a flight, an offense punishable by a maximum fine of 5 million won ($4,533).

Assaulting a flight crew member during a flight could result in a jail term of up to five years.

The ministry said it would also take disciplinary measures against Korean Air, which could result in a suspension of the New York-Incheon flight for up to 30 days or a maximum fine of some 2.1 billion won.

Korean Air and its owner family have come under public criticism over the nut incident. Over 600 people have signed an online petition demanding the government ban the airline from using the country’s name in its corporate name.

Shares of Korean Air have dipped 5 percent since the incident as of Wednesday while shares of Hanjin KAL, the de facto holding company of Korean Air and Hanjin Group, slipped 5.47 percent over the cited period.

Prior to the nut-rage case, Korean Air shares had surged 19.05 percent in December on favorable market conditions from plunging oil prices. (Yonhap)