Federal investigators say pilot error and a non-functioning light atop a wind turbine are probable causes of a plane crash that killed four South Dakota men a year ago.

The single-engine Piper crashed April 27, 2014, when it struck a 330-foot-high wind turbine in fog ten miles south of Highmore.

The crash killed the pilot and three cattlemen returning from a sale in Texas.

A National Transportation Safety Board report released this week says the pilot's decision to fly low in deteriorating weather and the non-operating light on the turbine were likely causes. No problem was found with the plane.

Killed were pilot Donald "D.J." Fischer, of Gettysburg; and cattlemen Brent Beitelspacher, of Bowdle; Logan Rau, of Java; and Nick Reimann, of Ree Heights.

Information from: Aberdeen American News

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