South Korea's top court kept a Korean Air heiress out of prison Thursday in the final verdict on the "nut rage" incident that triggered national uproar in 2014.

Cho Hyun-Ah, a daughter of Korean Air chief Cho Yang-Ho and then the company's vice president, became infuriated when a flight attendant served her some nuts in a bag rather than in a bowl.

She lambasted the chief steward over the behaviour of his cabin crew and ordered the Seoul-bound flight, which had just left the gate in New York, to turn back so he could be ejected.

The incident caused fury at home and made global headlines, eventually prompting Seoul prosecutors to charge her with offences including violating aviation security and business practices laws.

Cho was initially convicted on most counts and sentenced to a year in jail, but she was freed after the appeals court cleared her of hampering an air route -- the most serious charge -- as the aircraft was still on the ground.

It maintained the more minor convictions, including interfering with business practices, but reduced her penalty to 10 months in prison, suspended for two years.

The Supreme Court upheld that ruling Thursday.

Cho, who resigned from her position soon after the incident, spent a total of five months in jail.

The case -- widely known as "nut rage" -- renewed criticisms in the South over the powerful, family-run conglomerates that dominate the world's 11th-largest economy.

The founding families of the business giants, called chaebol, have been criticised for running their global businesses like their personal fiefdoms with minimum scrutiny by regulators.

Park Chang-Jin, the chief steward who was ejected and forced to kneel before Choi while she hurled personal insults at him, was later demoted after speaking out against her. He filed suit against Korean Air last month.