Preliminary information suggests that the 29-year-old mechanic stole the Horizon Air Q400 and the crash occurred because the person was "doing stunts in air or lack of flying skills," the Pierce County Sheriff's Department said.
Witnesses reported seeing the plane being chased by military aircraft before it crashed near Ketron Island, southwest of Tacoma, Washington.
There were no passengers aboard.
The sheriff's department said they were working to conduct a background investigation on the man, whose name was not immediately released.
The man could be heard on audio recordings telling air traffic controllers that he is "just a broken guy."
The US Coast Guard was sending a 45-foot (14-metre) vessel to the crash scene after witnesses reported seeing a large plume of smoke in the air, Petty Officer Ali Flockerzi said.
The Q400 ix a turboprop aircraft with 76 seats.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)