BUTTE, Mon.-- Another plane related incident this one close to Washington.
Witnesses in Butte, Montana describe what they saw.
"It just dropped off, it just dropped and plowed into the ground," said Martha Guidoni, a witness.
"All of a sudden I saw this big black fireball, boom," said another witness.
The single engine Pilatus PC 12 left Oroville, California and was heading to Bozeman, Montana. NTSB staff say they still don't know why the pilot diverted to Butte.
"At this point there is nothing for us to understand why he may have decided to make this decision to divert," said Mark Rosenker, with the NTSB.
The plane was registered to Eagle Cap Leasing Incorporated in Enterprise, Oregon.
Staff at the Enterprise Municipal Airport say the company flies aircraft in an out of their airport. But the owners live in California.
The plane can fit between 9 and 12 people. But there might have been some extra children sitting on laps.
"We don't know the ages yet, but we're going to have to try to understand, how and why there were an additional three people on board of the aircraft," said Rosenker.
NTSB staff say they'll look at all possible causes including weight, mechanical failure, and weather.
"We will be looking more carefully at the weather pattern, radar, all, everything we can possibly find out," said Rosenker.