The daughter of Korean Air's chairman was jailed for one year Thursday over a notorious "nut rage" incident that triggered an uproar over the behaviour of South Korea's business dynasties.

The district court in Seoul convicted Cho Hyun-Ah of violating aviation safety law by forcing a taxiing New York-Seoul KAL flight to return to its departure gate on December 5.

Cho, who was the airline's executive vice president at the time, had insisted on expelling the chief purser from the plane after taking exception to being served macadamia nuts in a bag, rather than a bowl.

The 40-year-old had treated the flight "as if it was her own private plane", Justice Oh Sung-Woo said, adding that the case had become the object of international ridicule and "damaged the dignity" of the country.

Cho treated employees "like feudal slaves" and failed to show "the slightest respect" for other people, the judge said.

Cho, clad in a pale green jail suit and with her head bowed so that her hair partially obscured her face, occasionally reached up to wipe away tears as the judge read his ruling.

'Deeply sorry'

"I am deeply sorry for what I did... I displayed my anger without control," she said in a letter of apology read out by the judge.

"I don't know how I can ever be forgiven," the letter said, adding that her six weeks in trial custody had allowed her to learn "respect for other people" from her fellow detainees.

Despite Cho's expressions of repentance, Oh questioned whether she was truly remorseful for her behaviour.

She was also convicted of assault on the cabin crew.

The chief steward, Park Chang-Jin, had testified that Cho had made him kneel and beg for forgiveness while jabbing him with a service manual.

Prosecutors in the trial had asked for a three-year sentence, but Oh said he had taken into account that no lives had been jeopardised in the incident, as well as the fact that Cho had two young children and that her personal and professional reputation had been shattered.

It was not immediately clear if Cho would choose to appeal.

Dismissing defence arguments to the contrary, the court ruled that an aircraft should be deemed "in flight" from the moment it begins to move and that Cho was therefore guilty of illegally altering the course of a plane.

She was acquitted of obstruction of justice charges related to allegations that she had pressured KAL staff to lie about the incident.

Another defendant, also a KAL executive, was convicted of forcing the flight crew to give false testimony and was jailed for eight months.

Spoilt and arrogant

The case triggered a huge public backlash.

Cho was seen as emblematic of a generation of spoilt and arrogant offspring of owners of the giant family-run conglomerates, or "chaebols", that dominate the South Korean economy.

Like Cho, many are given senior positions in the family business, sometimes after a token period "learning the trade".

In the past, chaebol owners have appeared to be above the law. Those convicted of gross fraud have either received lenient sentences or been granted pardons after just a short time in jail.

Cho had resigned from all her posts and publicly apologised for her behaviour, which her father and KAL chairman Cho Yang-Ho criticised as a "foolish act".