The Beechcraft Bonanza vanished in the Chattahoochee National Forest on May, 30, 2011, while on a sightseeing ride during the 50th reunion of the Gilmer County High School Class of 1961.
Now, as part of a lengthy investigation that's still ongoing, federal investigators have zeroed in on an instrument that measured the plane's altitude.
Investigators haven't determined what caused the crash that killed pilot Phil Key of Pataskala, Ohio; and Ellijay residents Patricia Smith; Woody Pierce and Mattie Pierce.
A recent report by the National Transportation Safety Board states that two medications were found in the pilot's system which they say can cause impaired judgment.
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