OSHKOSH, Wis. — Federal investigators say the Marshall pilot of a seaplane that crashed on Lake Winnebago in eastern Wisconsin last month, killing himself and a passenger, tried to take off for Minnesota despite warnings about rough water.

The plane crashed July 27 while trying to take off from the Experimental Aircraft Association’s seaplane base near Oshkosh during the group’s annual convention. The crash killed the pilot, 84-year-old Ray Johnson, of Marshall, and 71-year-old Diane Linker, of Sauk Rapids. A second passenger survived.

Johnson was a southwest Minnesota businessman with a long career in aviation and aviation services. Johnson was the founder of Midwest Aviation in Marshall, and was a flight instructor.

The crash was under investigation by the National Transportation Safety Board. The NTSB’s preliminary report Monday doesn’t pinpoint a cause for the crash, according to Associated Press reports. But the report says the pilot was taken onto the lake by boat after personnel expressed concern about the high waves. But Johnson still asked for the seaplane to be refueled to fly to Marshall.