ATLANTA (AP) — Federal authorities say a partial loss of engine power likely caused by debris in the fuel system caused a single-engine plane to crash into a metro Atlanta highway last year, killing all four on board.

Greg Byrd III of Asheville, North Carolina, his sons 27-year-old Christopher Byrd and 26-year-old Phillip Byrd and Christopher’s fiancee, 27-year-old Jackie Kulzer of metro Atlanta, all died in the fiery May 2015 crash. The plane slammed into a median wall on Interstate 285 about two minutes after departure from DeKalb Peachtree Airport.

The Atlanta Journal-Constitution reports (http://on-ajc.com/2cem3Cj ) that the National Transportation Safety Board on Tuesday announced that an investigation revealed that the fuel manifold wasn’t operating normally and was contaminated by debris. The report says that likely “resulted in fluctuating power indications.”

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Information from: The Atlanta Journal-Constitution, http://www.ajc.com