RAMSEY (AP) -- Federal investigators have concluded the pilot of a small plane was flying too low over the Mississippi River last October just before crashing into the water, killing himself and his wife.

The National Transportation Safety Board in its final report on the crash says the single-engine Cessna struck power lines over the Mississippi near Ramsey and plunged into the river.

Investigators say the plane was flying at or below the height of the trees on the river banks _ or less than 100 feet. The Federal Aviation Administration prohibits operating an aircraft less than 500 feet in an uncongested area.

Forty-seven-year-old Chad Rygwall and 48-year-old Jill Rygwall, of Princeton, were killed.