PETALUMA (KRON) — National Transportation Safety Board announced Tuesday that witness heard a heard a “pop” sound before a plane crashed into a Petaluma field killing its pilot.

The NTSB issued a preliminary report on the April 3 crash that killed the pilot, 51-year-old David Michael Wright of Petaluma.

The agency said the report is subject to change and might contain errors that will be corrected when its final report is released.

Witnesses said the Quicksilver Enterprises Inc. MXL II aircraft was flying at 1,000 feet south of the Petaluma Municipal Airport when they heard the pop and saw the wings fold upward, NTSB officials said.

Wright, a student pilot who was the only one aboard the plane, did not file a flight plan, and it’s unknown what time the plane took off from the airport, according to the NTSB.

The plane crashed in a field about 1.3 miles southeast of runway 29. Debris, including a propeller and engine, was found within 15 feet of the main wreckage, NTSB officials said.