Sanford N. McDonnell, the former chief executive of McDonnell Douglas who turned his family’s troubled aerospace company into one of the country’s leading defense contractors, died March 19 at his home in Clayton, Mo. He was 89.

The death was announced by Boeing, which acquired St. Louis-based McDonnell Douglas in 1997. Mr. McDonnell had pancreatic cancer, his family told the St. Louis Post-Dispatch.

Under “Sandy” McDonnell’s stewardship, McDonnell Douglas supplied the military with some of the most advanced aircraft made, including supersonic fighter jets, attack helicopters and self-guiding cruise missiles.

Mr. McDonnell became chairman and chief executive of McDonnell Douglas in 1980 after the death of his uncle, James S. McDonnell Jr., who had founded the company in 1939.

The business made airplane parts during World War II and later sent the first Americans to outer space as the manufacturer of the Mercury spacecraft.

Mr. McDonnell joined the firm in 1948 after Army service in World War II. He worked as a stress engineer and later led the development of the F-4 Phantom II fighter jet, which had a crucial role in the Vietnam War.

In 1967, the McDonnell company merged with Douglas, a commercial plane manufacturer that produced the popular DC-3 airliner. Four years later, Mr. McDonnell became president of the firm.

Although merged, McDonnell Douglas basically functioned as separate companies. Mr. McDonnell struggled for much of his tenure to keep his uncle’s business from falling apart.

The McDonnell side, headquartered in St. Louis, handled defense contracts for military aircraft. The Douglas operation, based in Long Beach, Calif., made commercial planes but struggled against heavy competition from Boeing and Lockheed.

From 1967 to 1984, the Douglas operations never turned a profit and lost more than $500 million.

During the 1970s, a war between McDonnell Douglas and Lockheed to build a superior wide-body airliner nearly put both companies out of business. Neither plane — the Lockheed L-1011 nor the McDonnell Douglas DC-10 — was a major success.

Ultimately, Lockheed dissolved its commercial air operations while McDonnell Douglas lost millions of dollars developing the DC-10. During the 1970s, the DC-10 was involved in several catastrophic air disasters.

In 1974, a Turkish Airlines DC-10 crashed outside of Paris after a cargo door opened and destabilized the plane. A total of 346 people were killed. At the time, it was the deadliest commercial air crash in history.

Then, in 1979, an American Airlines DC-10 crashed near Chicago when an engine detached from a wing, killing 273 people in what was then the worst air crash in American history.

Airlines began canceling orders for the DC-10 because thousands of passengers refused to fly on it.

To keep McDonnell Douglas afloat, Mr. McDonnell engaged in what Forbes magazine once called “creative financing.”

Mr. McDonnell had seen that many airlines had been hit hard by a recession and were keeping older planes in their fleets to keep costs down. Mr. McDonnell came up with a plan to begin leasing planes to airlines with a no-commitment option to buy them.

The leases hurt McDonnell Douglas in the short-term but kept the business alive. “You have to credit Sandy McDonnell and his board,” Forbes magazine wrote in 1982, “with the kind of nerve and farsightedness that is pretty rare in U.S. business these days.”

On the military side, Mr. McDonnell was far more successful. He secured lucrative contracts with the Pentagon that earned the company billions of dollars to offset commercial losses.

While Mr. McDonnell was chief executive, McDonnell Douglas built the Air Force’s F-15 Eagle fighter jet. He played a pivotal role in lobbying successfully for the sale of F-15s to Saudi Arabia and Israel.

He oversaw the 1984 acquisition of Hughes Helicopters, which made the Army’s AH-64 Apache helicopter. The company also supplied the Navy and Marine Corps with the F-18 Hornet and the AV-8B Harrier as well as the Tomahawk cruise missile.

All of those aircraft have been used in combat in Afghanistan, and U.S. Navy ships launched more than 100 Tomahawk missiles against Libyan air defenses in 2011 during the effort to expel Col. Moammar Gaddafi from power.

By the time Mr. McDonnell retired in 1988, the company’s revenues had reached $12.7 billion.

Sanford Noyes McDonnell was born Oct. 12, 1922, in Little Rock. He was a 1945 economics graduate of Princeton University. He received a second bachelor’s degree, in mechanical engineering, from the University of Colorado in 1948 and a master’s degree in applied mechanics from Washington University in St. Louis in 1954.

A complete list of survivors could not be determined.

Mr. McDonnell was described in profiles as quiet and unassuming. But not always. He had a passion for Scottish music, played the bagpipes and hosted a Highland-themed fundraiser for the St. Louis Opera Theatre Gala in 1991. He greeted the guests in a traditional tartan kilt.

“Hoot Mon! Laddies and lassies of the McOpera Clan,” Mr. McDonnell said. “I think of us as a conservative city, but the first time I wore this kilt, three or four different women came up and peeked under my kilt, and then the women became very conservative themselves when I wanted to return it.”