SEOUL (Reuters, AFP) - The daughter of the boss of Korean Air, on trial in a case popularly known as "nut rage", treated flight crew like "feudal slaves", a chief steward said in court on Monday.

Heather Cho, daughter of Korean Air Lines chairman Cho Yang Ho and the former head of in-flight service, is on trial for breaking aviation laws and conspiring with other company executives to force crew members lie about the Dec 5 incident.

Prosecutors are seeking a three-year prison term if she is convicted.

Cho had demanded the chief steward, Park Chang Jin, be removed from a flight at New York's John F. Kennedy airport after a first class flight attendant served her macadamia nuts in a bag, not on a dish.

The plane, already taxiing towards the runway, returned to the gate.

Park said Cho "was like a beast that found its prey gritting its teeth as she became abusive, not listening to what I had to say at all".

"I don't think Cho showed an ounce of conscience, treating powerless people like myself like feudal slaves, forcing us to sacrifice and treating it as if it was the natural thing to do," Park said, fighting back tears. Park and prosecutors had said he was forced to kneel down and Cho poked his palm several times with a folder.

He appeared in court in his uniform after returning to work over the weekend after a leave of absence.

Cho resigned from her posts at the airline, including vice-president, in the face of public anger and ridicule over her behaviour, which raised questions about the power of the country's "chaebol" conglomerates.

On Monday Cho apologised for her "rash" conduct but insisted the affair originated from the breach of the service manual by flight attendants. She denied using violence against Park and said the pilot made a final decision to force him off the plane.

Her lawyers have argued that there had been no breach of safety laws, given that the plane had not even reached the runway when it turned back. Cho has been in custody since December 30.

Prosecutors also demanded a two-year jail sentence each for a company executive charged with evidence-tampering and a transport ministry official, who is accused of leaking details of a government probe into the case.

Cho's father apologised in court on Friday to Park and promised he would not face any reprimand.

Heather is the oldest of Cho Yang Ho's three children. Her siblings are also executives with the airline.