The right wing of a Cessna 208B broke from the aircraft in flight before the plane crashed Friday into a field in Snohomish, killing the four people onboard, the National Transportation Safety Board said Monday.

The wreckage, including the separated wing, which landed about 200 yards from the fuselage, has been recovered and taken to a facility for reconstruction, according to the NTSB. A preliminary crash report is expected in two to three weeks, though a full investigation could take up to two years.

The small plane took off from Renton Municipal Airport around 9:30 a.m. and crashed in a field east of Harvey Airfield in Snohomish County around 10:20 a.m., the NTSB said. There was a post-crash fire.

Raisbeck Engineering of Seattle described the plane crew as two “highly experienced” test pilots, a flight-test director and an instrumentation engineer. The crew was flying the plane in preparation for modifying the aircraft, Raisbeck President Hal Chrisman said in an emailed statement over the weekend.

NTSB investigators are collecting plane maintenance records and information about the pilots’ licenses, ratings and history, the safety board said.

The Snohomish County medical examiner has not yet identified the victims. Chrisman has declined to comment on the crew members involved in the crash.