HUMBIRD, Wis. (AP) -- Investigators say poor weather likely figured in a plane crash near Humbird in Jackson County that killed a Sheboygan chiropractor and his son.

The National Transportation Safety Board released a preliminary report Thursday.

Pilot David Holtrop and his 16-year-old son Maxwell took off from near St. Paul, Minn., to return home from a paintball convention when the crash happened about 5:45 p.m. June 7.

The NTSB said data showed instrument meteorological conditions prevailed, but David Holtrop was a non-instrument rated pilot.

Witnesses said they heard but did not see an airplane. One reported hearing an aircraft engine increase and decrease rapidly before the sound of a crash. The witness said it was raining and foggy.

The NTSB will release a final report later.