ASHLAND, Wis. — A single-engine plane that crashed in northwestern Wisconsin this month, killing both people aboard, bounced "out of control" on the runway before eventually exploding, according to an investigative report.

The National Transportation Safety Board is investigating the June 15 crash, which killed La Crosse physician Richard Renwick, 63, and his brother, 58-year-old Bruce Renwick of Waunakee. NTSB's final report could take 12 to 18 months, but a preliminary report released Friday suggests there were difficulties with the landing, the La Crosse Tribune reported ( ).

Richard Renwick, who was piloting the 1965 single-engine Piper Comanche, took off with his brother about 11 a.m. from the La Crosse Municipal Airport. They stopped near Ashland and then headed to Madeline Island about 15 miles away.

The crash occurred about 6:30 p.m. just short of the runway at Major Gilbert Field Airport near La Pointe, the NTSB report said.

A witness told investigators he "heard an airplane engine, heard 'squealing,' and heard sounds like screeching tires," the report said. The witness looked at the runway "and saw the airplane 'bouncing out of control.'"

NTSB investigators checked out the runway and found it had slash marks consistent with contact with the propeller.

The plane then began climbing, and the witness thought it was going to attempt another landing. He turned around until he heard an explosion, the report said.

"He looked back, saw a plume of black smoke and called 911," the agency said.

Richard Renwick was an obstetrician at the Gundersen Health System. Bruce Renwick was a psychiatric nurse.