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Smoke comes up from the site of a small plane crash that killed on person off Marsh Creek Road in Byron, Calif., on Tuesday Oct. 23, 2012. (Dan Rosenstrauch/Staff)

BYRON -- A small plane that crashed last month, killing the pilot and a passenger, had just taken off from a private Brentwood landing strip and was flying at about 1,000 feet when it nosed over and spun until it hit the ground, witnesses told investigators.

The National Transportation Safety Board did not give a specific cause for the Oct. 23 crash in its preliminary report, which was released Wednesday. The crash killed Brentwood residents David S. Behne, 57, and Larry Strobel, 56.

Behne, the registered owner of the plane, was piloting the craft when it crashed, according to the Contra Costa County Sheriff's Office. Strobel, a longtime friend, was also rated as a private pilot, according to the NTSB.

The plane crashed and burned in a field about four miles south of the private Brentwood landing strip Behne had registered as "Funny Farm Airport." Behne, a mechanical engineer, had built the experimental plane himself and flew frequently, friends said.

An NTSB investigator confirmed that the plane's "major structural components" were all present at the crash site. The Glasair III is a 21-foot two-seater, with a top speed of 327 mph and a 23-foot standard wingspan.

Witnesses told the NTSB investigator that the plane suddenly nosed over as it flew at about 1,000 feet, spinning to the left with its nose pointed slightly down. The spin continued until the plane struck the ground and caught fire.

Weather conditions were clear and mild, with light winds, at the time of the 2 p.m. crash, according to the National Weather Service.

Behne, who flew daily, had most recently worked on commercial satellites used by television companies while contracting at Space Systems/Loral in Palo Alto.

Strobel was the owner of L.D. Strobel Co. in Concord, a wireless and utility construction company that has completed 5,000 projects, including communications towers in Hawaii and San Francisco, since its founding by Strobel in 1987, according to the firm's website.

The plane's wreckage has been placed in storage. The NTSB will continue investigating, with the help of the FAA, and will likely take months to release a final report on the crash.

Contact Daniel M. Jimenez at djimenez@bayareanewsgroup.com. Follow him at Twitter.com/DMJreports.