The message reading "I will certainly take revenge!" was sent by Cho Hyun-Min, 31, on December 17 when Korean Air (KAL) heiress Cho Hyun-Ah was summoned by prosecutors for questioning.
Prosecutors revealed its contents yesterday after Cho Hyun-Ah was formally arrested on charges including violation of aviation safety law, coercion and interference in the execution of duty, Yonhap news agency said.
The 40-year-old has been accused of forcing the chief purser off a December 5 New York-Seoul flight and of compelling the taxiing plane to return to the gate so he could disembark in a case that has caused uproar in South Korea.
"I'm really sorry beyond words for my text message... I would not make any excuses. It's all my fault," Cho Hyun-Min, who holds executive-level positions at the flag carrier and its sister firms, wrote on Twitter.
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The subject of her vengeance was not clear, but Yonhap and newspapers speculated she was talking about the chief purser, who has criticised Cho Hyun-Ah in TV interviews.
KAL's reputation has been hit hard by the detention of the chief's daughter and another unidentified company executive, who was accused of destroying evidence from the incident.
The transport ministry has vowed to sanction the airline with a flight ban, most likely on the New York-Seoul route, that could last for up to a month, or with fines of up to USD 2 million.
Separately, the ministry has vowed to punish eight of its officials after admitting their investigation into the incident was unfair.
On Monday, Shin Un-Chul, a ministry auditor, said the inclusion of KAL staff in the probe may have intimidated witnesses.
A ministry investigator was arrested last week for leaking details of the investigation to KAL officials.