PIGEON FORGE, Tenn. (AP) — The National Transportation Safety Board says a deadly helicopter crash in Tennessee two years ago had been caused by a failing fuel pump.

News outlets cite the board's final report as saying the wear on the pump was enough to stop fuel from getting to the engine. It says the wear was likely accelerated by incorrectly sized part that may have allowed grease to escape the pump.

The pilot and four passengers died in the April 2016 crash in Pigeon Forge. Pilot 38-year-old Jason Dahl was killed along with 21-year-old Michael Glenn Mastalez, 49-year-old Johna Morvant, and her two children 22-year-old Peyton Rasmussen and 18-year-old Parker Rasmussen.

The helicopter had caught fire during the crash. The report says it wasn't equipped with a crash-resistant fuel system designed to prevent fires.