SEOUL - The daughter of the chairman of Korean Air Lines, whose outburst over the way she was served nuts in first class prompted widespread outrage and ridicule, was in custody on Wednesday facing charges of violating aviation safety.

Heather Cho, 40, former head of in-flight service, had demanded the chief steward be removed from the flight at John F. Kennedy airport in New York on Dec. 5 after another flight attendant in first class served her macadamia nuts in a bag, not a dish.

In what media dubbed the "nut rage" incident, the Airbus A380, which had pushed back from its gate, returned for the chief attendant to disembark, arriving in South Korea 11 minutes late.

"The necessity for detention is recognized as the case is grave and there has been an attempt to systematically cover up charges from the beginning," Lee Kwang-woo, a judge at Seoul Western District Court, said in a text message.

She can be held for up to 20 days before prosecutors bring charges.

The Transport Ministry had concluded that Cho abused flight attendants and that airline officials may have tried to cover up the episode.

Another airline official was detained over allegations that he abetted perjury and obtained information on the ministry's probe to update Cho.

The Cho family, one of South Korea's most powerful, faced fresh criticism on Wednesday after media said her sister, also an executive with the airline, had sent a text message to Cho on Dec. 17 saying: "I will surely take revenge."

Emily Cho apologised on Wednesday on Twitter: "I am sorry beyond words for the content of my text message that was reported in today's newspaper. I don't want to make any excuses. It is all my fault".

Korean Air had no comment and said that Emily Cho was not available to comment.

Flanked by prosecution officials after the court's detention order late on Tuesday, Heather Cho said "sorry" several times, her head bowed.

The Transport Ministry came under fire after revelations that some of its officials leaked information to the company.

Cho's case aggravated resentment towards family-run conglomerates, stirred by their dominance of the economy and a widening wealth gap.

An official at the facility where Cho was being held said she would not receive special treatment. "Whoever comes here, whether it is Cho Hyun-ah (Heather Cho)...they are treated equally."