SHELDON, Iowa -- Two witnesses reported hearing a plane's engine "coughing, sputtering and missing" before it crashed in northwest Iowa last month, killing three Wisconsin men.

That's according to a preliminary report from the National Transportation Safety Board, which said the witnesses saw the plane at a low altitude. They also reported that the engine quit, restarted and quit again.

The three men died June 23 when the single-engine Piper crashed during a flight from Fort Atkinson, Wis., to a hunting trip in South Dakota.

The plane touched down in a cornfield near Sheldon, traveled about 100 feet and hit a ditch near a gravel road before nosing over.

The men killed were: 64-year-old Francis Allegretti of Cambridge, Wis.; 60-year-old Thomas Boos of Fort Atkinson, Wis.; and 65-year-old Malcolm McMillan of Milton, Wis.