The building frame that collapsed Wednesday was the skeleton of an engineered steel building that was to become a new hangar for the Jackson Jet Center next to the Boise Airport.

The collapse killed three people and injured nine, with five in critical condition, the Boise Fire Department said Wednesday night.

How the building collapsed remained unclear, and it’s a key question for investigators. Engineered buildings are common in industrial and warehouse construction, thanks to their economy and efficiency. This one was to have been a single story tall.

The collapse of the frame and a crane happened at a site for which permit-application documents provide varying addresses, including 4049 W. Wright St. and 4125 W. Wright St. The site is next to the four buildings that make up the jet center, between an old Federal Aviation Administration building and an office for Firehawk Helicopters. The jet center and Firehawk are easily visible to drivers on nearby Interstate 84.

An engineered building is a kind of standardized kit made to be assembled on site. A permit filing with the city of Boise shows that the building was to have 39,000 square feet and be erected atop a concrete foundation.

The building was to be an expansion of the jet-servicing business, which provides maintenance, aircraft parts and charter flights.

“These hangars are necessary for continued Jackson Jet operations following the Boise Airport requiring Jackson Jet to vacate their existing hangars in order to accommodate planned airport parking facilities,” according to an application from Boise architecture firm Glancey, Rockwell and Associates, which prepared design drawings of the hangar.

The 45½-foot-tall hangar was projected to cost about $6.2 million, according to a filing with the city. Plans called for vertical metal siding and a blue accent strip along the top portion of the building.

“The architectural design is consistent in terms of massing and design with other similar use buildings in this area,” according to a summary from the city’s Planning and Development Services Department.

Boise Fire Department Operations Chief Aaron Hummel said at a news conference that officials were not sure what happened. He called the collapse “global” and “catastrophic.”

“They were still working on some of those structural components, tying those together,” Hummel said.

“I don’t know exactly what caused it, but it did impact the crane, so the crane collapsed as well,” he said.

A call to John D. Jackson, patriarch of the Meridian-based Jackson-family business empire that includes the jet center, Jackson’s Food Stores and Jackson Energy, was not immediately returned. Neither was an email to his son, Jeff Jackson, who applied for the building permit.

Jessica Flynn, CEO of Red Sky PR, said in a news release on behalf of Jackson Jet Center that the company did not know what caused the hangar collapse.

The Meridian-based construction company Big D Builders was listed as the general contractor for the hangar. Big D Builders declined to comment.

A call to Glancey, Rockwell and Associates went unanswered and ended without the opportunity to leave a voicemail message.

UPDATE: 3 dead, 9 injured, some critical after Boise building collapses near airport

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