A rendering of the renovation of “America by Air,” one of the Smithsonian Air and Space Museum’s main attractions. (Smithsonian National Air and Space Museum)

In a remarkable joint venture, nine commercial airlines have donated $28 million to the National Air and Space Museum to support the remaking of an exhibition that traces the history of commercial aviation, the museum announced Wednesday.

The rare collaborative gifts from competitors in a cutthroat industry will fund the renovation of “America by Air,” one of the Smithsonian museum’s main attractions. The exhibition features artifacts that trace the evolution of flying, from uniforms and models to Douglas DC-3 and DC-7 planes and the nose of a Boeing 747 that visitors can enter.

The donations are among the first major private gifts to the almost $1 billion renovation of the city’s most popular museum, located on the southern edge of the Mall.

“This is really a breakthrough,” said museum director Gen. J.R. “Jack” Dailey (Ret.). “The airline industry, as competitive as they are, here they have come together.”

Dailey said the joint gift is also important because it comes from new donors to the museum, which opened in 1976. Commercial airlines have contributed in-kind donations, but nothing on this scale.

The donations represent a bright spot for a project that has grown increasingly more complicated and expensive. Smithsonian officials have asked Congress for the bulk of the costs, about $676 million, and have pledged to raise $250 million from private donors. Construction is expected to begin this summer and will take seven years because the museum will remain open as the work is done.

“The airlines have never been major players, so this is new money,” said Dailey, who retires this week after 18 years at the helm. “It’s important to us, gives our previous donors a breather.”

American, Delta and United airlines are the lead donors, followed by JetBlue, Alaska, Frontier, Hawaiian and Spirit airlines. Southwest Airlines made a gift last year that will support a new welcome center. The gallery will close this summer and is expected to reopen in 2021.

The plan calls for upgrading the building’s mechanical systems and replacing its stone exterior, repairs that are usually funded by the government. The work will be completed in stages, and museum officials will refresh all 22 galleries as it proceeds.

“We kind of took advantage of the chaos,” Dailey said. “When we open again it will be brand-new, inside and out.”

The museum is forging ahead with the largest capital project in its history despite not having secured funding from Congress. The museum has received funds for new storage, but the first installment of construction money is part of the current fiscal year’s spending bill that is still being negotiated. Smithsonian officials are facing deadlines this spring to purchase materials, including marble and glass for the exterior. Work may be delayed if they can’t buy what they need.

David Rubenstein, chairman of the Smithsonian Board of Regents, acknowledged the uncertainty but said he sees positive signs from Capitol Hill. “There is a lot of support. The Smithsonian is popular,” he said. “Congress likes the idea of joint ventures.”