SEOUL (AFP) - South Korean prosecutors urged an appeals court on Monday to increase the prison sentence given to a Korean Air heiress for disrupting a flight in a rage over macadamia nuts to three years.

Cho Hyun Ah, the eldest daughter of KAL's chairman, was jailed for a year in February after a district court found her guilty of violating aviation safety by forcing a taxiing New York-Seoul Korean Air Lines (KAL) flight to return to its departure gate.

At the High Court in Seoul on Monday, Cho's lawyers disputed the lower court ruling that an aircraft should be deemed "in flight" from the moment it begins to move.

They argued that Cho should not have been found guilty of altering the plane's flight because it had barely left the gate when she forced it to return. Her defence lawyers also said their client was "regretful".

But prosecutors called for the court to extend her one-year jail term to three, saying Cho's apologies "were not sincere".

"Judging from testimonies from the flight crew and her confession, it's illogical to say that she did not know the plane was in flight," the prosecution said.

Cho, who was a KAL vice president in charge of in-flight service at the time of the December 5 incident, had become enraged after a flight attendant served her some nuts in a bag, rather than on a plate.

She lambasted the chief steward over the behaviour of his cabin crew and then insisted the plane return to the gate so he could be removed from the flight.

The 40-year-old's actions invited overseas ridicule and domestic embarrassment.

Many South Koreans saw her behaviour as emblematic of a generation of spoilt and arrogant offspring of owners of the giant family-run conglomerates, or "chaebols", that dominate the national economy.

She was also convicted of assault on the cabin crew, with the chief steward, Park Chang Jin, testifying that Cho had made him kneel and beg for forgiveness while jabbing him with a service manual.

The flight attendant who served the now infamous nuts has since filed a civil lawsuit, alleging Cho attacked, threatened and screamed obscenities and then pressured her to cover up the incident by lying to government regulators.

At the February trial Cho was acquitted of obstruction of justice charges.