WINDSOR LOCKS, Conn. (CBS/AP) — Federal investigators are trying to figure out what caused a B-17 bomber to crash at Bradley Airport Wednesday killing seven people.

The four-engine, propeller-driven World War II-era plane had 13 people on board when it went down after having engine trouble on takeoff.

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The National Transportation Safety Board sent a team of 10 to investigate the cause of the crash. They expect to be there about a week. “This was a significant tragedy and from the scene I am surprised that people survived,” Jennifer Homendy of the NTSB told CBS News.

Homendy said a lot was accomplished in their first full day of investigating Thursday. The NTSB has requested inspection, maintenance and crew training records, which they will now analyze.

Even though so much of the plane was destroyed in the crash, investigators were able to salvage key components including the engines and tail.

The B-17 struggled to get into the air and slammed into a maintenance building as the pilots circled back for a landing, officials and witnesses said. There were 10 passengers and three crew members on the plane, which was operated by the Collings Foundation, an educational organization based in Stow, Massachusetts.

Six of the 13 survived, but three of them were critically hurt. A former police officer and an insurance analyst were among the victims. The full list of names was released Thursday.

Homendy said the plane made contact 1,000 feet from runway 6, and hit 30 breakaway approach lights before it hit the maintenance building. Video showed the plane approaching the runway “right wing down” before the crash, Homendy said.

Connecticut Public Safety Commissioner James Rovella said hours after the crash that some of those on board were burned, and “the victims are very difficult to identify.”

One person on the ground was also hurt in the crash and a firefighter involved in the response suffered a minor injury. No children were on the plane.

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The death toll of seven could rise, Rovella said. He said some lives were likely saved by the efforts of people including a person who raced to help the victims and people on the plane who helped others to escape the fire by opening a hatch, Rovella said.

“You’re going to hear about some heroic efforts from some of the individuals that were in and around that plane,” he said.

A World War II-era B-17 bomber crashed October 2 while trying to land at Connecticut’s Bradley International Airport. (WBZ-TV)

The Collings Foundation brought its Wings of Freedom vintage aircraft display to the airport this week.

The vintage bomber, also known as a Flying Fortress, one of the most celebrated Allied planes of World War II,  was used to take history buffs and aircraft enthusiasts on short flights, during which they could get up and walk around the loud and windy interior.

The crash reduces to nine the number of B-17s actively flying, said Rob Bardua, spokesman for the National Museum of the U.S. Air Force, near Dayton, Ohio.
Boeing-built B-17 Flying Fortresses, 74 feet long, with a wingspan of 104 feet, to be used in daylight bombing raids against Germany during the war. The missions were extremely risky, with high casualty rates, but helped break the Nazis’ industrial war machine.

The B-17 that crashed at Bradley Airport October 2. (Photo credit: Craig Michaud)

The B-17 that went down was built in 1945, too late to see combat in the war, according to the Collings Foundation. The foundation bought it in 1986.

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(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)