A scene from the crash of a small jet in Farmington on Sept. 2, 2021.?

FARMINGTON — While no official determination has been made about what caused the plane crash that killed the pilots and two passengers, investigators from the National Transportation Safety Board noted in a preliminary report released Tuesday that the plane’s parking brake was on.

The plane, a Cessna 560 jet, crashed into a Trumpf Inc. building in Farmington shortly after takeoff from nearby Robertson Field Airport in Plainville on Sept. 2. The crash killed pilots Mark Morrow, 57, of Danbury, and William O’Leary, 55, of Bristol, along with the passengers, Courtney Haviland, 33, and her husband, William Shrauner, 32, both doctors from Boston.

According to the three-page NTSB report, two witnesses saw the plane take off and one remarked that it was “going slower” than during normal takeoff. Another witness reported seeing a blue puff of smoke from the backside of the airplane when it was about two-thirds of the way down the runway, the report stated. One witness recalled telling a friend that something was wrong, the report stated.

Investigators visited the small airport and found tire skid marks from the right main landing gear on the runway then about 100 feet down noticed marks from the left main landing gear, the report read. The marks continued down the runway and onto a short patch of grassy terrain off the departure end of the runway, investigators noted.

A witness reported seeing the plane take off and not gain altitude before it hit a power line pole, the report read.

Investigators reviewed what was left of the airframe of the plane and its cockpit. While no “anomalies” were found on the frame or control panel, the investigators wrote “the parking brake handle in the cockpit, and the respective valve that it controlled, were both found in the brake set position.”

The plane, according to investigators, had been heading to Dare County Regional Airport in North Carolina.

The plane, after hitting the power line, eventually crashed into the Trumpf Inc. building, setting the plane and the building ablaze. On the ground, NTSB said one person was seriously injured and three others suffered minor injures.

It was unclear Tuesday when a full report on the accident would be released, but typically NTSB investigations take several months.

At the time of the crash, Haviland was pregnant. She and Shrauner, who had a young son, met at Weill Cornell Medical College in New York City, according to a family spokesperson. Haviland, who grew up in Farmington, joined MassGeneral Hospital for Children in 2016 as a resident. Shrauner was a second-year fellow at Boston Medical Center.

Both the pilots, O’Leary and Morrow, were well-known in the area for flying.

Nicholas Rondinone is the assistant managing editor for breaking news at Hearst Connecticut media. A Connecticut-native, he has covered breaking news in the state for the past 8 years.