Delta Air Lines bought a 4.3% stake in Korean Air Lines Co’s parent company and said it wants to raise it to 10%, giving a boost to the management of South Korea’s top carrier that seeks to thwart a local activist fund’s challenge.

Shares of the parent, Hanjin Kal Corp, slumped 8% on Friday, as Delta’s move dashed investor expectations of a battle to control the family-run group that has driven up shares since the death of patriarch Cho Yang-ho in April.

Korean Air, which has a joint venture with Delta, said on Friday that the stake buy intends to ensure the ‘stable management” of the company and support its leadership.

Should the No. 2 US carrier raise its stake to 10% in Hanjin Kal, the airline’s founding family and its allies will have a total stake of 39%, versus the 16% stake held by the activist fund, Korea Corporate Governance Improvement (KCGI).

“Delta played a role as a white knight for Hanjin,” Choi Nam-gon, an analyst at Yuanta Securities, said, noting that the share purchase was done despite the sharp share price rises of Hanjin Kal in recent months.

“Now it would be impossible for KCGI to take control of the group. The stake buy removes the chance of a management battle at Hanjin Group,” he said.

Korean Air shares fell 3% and its budget affiliate Jin Air Co slipped 0.7% in the wider market that was down 0.2%.

In April, the tycoon suddenly died at age 70, just weeks after shareholders decided to end his 27-year tenure on the airline’s board, in a show of growing shareholder activism in Asia’s fourth-biggest economy that has long been dominated by family-owned conglomerates.

The group subsequently appointed his only son Walter Cho, 43, as CEO and chairman, but the company has yet to inform regulators about a definitive succession plan. He and his two sisters have small stakes in Hanjin Kal, in which the late Cho has a 17.8% stake.

Against that backdrop, KCGI raised its stake to nearly 16%, fueling speculation about an impending ownership battle at the conglomerate.

KCGI did not have immediate comments on Delta’s stake buy.

Delta Chief Executive Ed Bastian said earlier this month he had “a lot of confidence” in Walter Cho, noting their friendship had gone back 20 years.

Korean Air has been plagued in recent years by a series of scandals involving its founding family members. Cho’s eldest daughter, Heather Cho, made headlines in 2014 when she lost her temper over the way she was served nuts in first class and ordered the Korean Air plane to return to its gate at a New York airport.

In April 2018, Cho’s youngest daughter Emily Cho faced a storm of public criticism for allegedly throwing a drink at a business meeting attendee.

Both resigned from their senior positions at the airline in the wake of the scandals. The younger Cho recently returned to the group as an executive at Hanjin Kal.

Delta’s stake buy comes as the US airline is expanding across Asia. It has said it sees Seoul’s Incheon International Airport, the hub of Korean Air, as a gateway for more destinations across the continent.

It did not disclose how much it paid for the 4.3% stake, worth about $88 million as of Thursday’s price. It also did not say who it bought the stake from or when it may raise it to 10 per cent.

The two firms formed a joint venture last year that includes 290 US destinations and over 80 in Asia. Atlanta-based Delta is growing internationally both through joint ventures - which allow airlines to coordinate fares and schedules while building a presence in new markets - and direct equity investments, which help airlines align their respective strategies.

Delta also owns stakes in Grupo Aeromexico, Air France KLM, China Eastern, Brazil’s Gol and Virgin Atlantic, and has been negotiating a stake in Alitalia.

Shares in Delta closed down 0.7% at $55.97 in New York on Thursday.

Meanwhile, the US Federal Aviation Administration on Thursday issued an emergency order prohibiting US operators from flying in an overwater area of Tehran-controlled airspace over the Strait of Hormuz and Gulf of Oman due to heightened tensions.

The order came hours after United Airlines suspended flights between New Jersey’s Newark airport and the Indian financial capital of Mumbai, which fly through Iranian airspace, following a safety review after Iran shot down a high-altitude U.S. surveillance drone.

The downing of the unarmed Global Hawk aircraft, which can fly at up to 60,000 ft (18,300 m), was the latest of a series of incidents in the Gulf region, a critical artery for global oil supplies, that included explosive strikes on six oil tankers.

Reuters