The National Transportation Safety Board is investigating a single-engine plane crash that killed 14 people — half of them young children — focusing on whether overcrowding was a factor in the crash.
Investigators say the turboprop airplane was designed to hold just 10 people — four fewer than were on board when it crashed in a Montana cemetery on Sunday.
Mark Rosenker, acting chairman of the NTSB, says investigators want to find out if the plane was over its weight limits. He says they are not jumping to conclusions that overloading was the cause of the crash.
Rosenker says children under 2 years old can sit on the laps of adults — but only one of the children was that young.
One witness reported that the plane jerked sharply to the left before it crashed some 500 feet from Bert Mooney Airport in Butte.
Kenny Gulick, 14, told CBS television that he thought he was watching a stunt plane because the pilot was making so many turns before the plane crashed Sunday night.
"He jerked the plane to the left too quickly and lost control of it, but that's just my guess," said Gulick. "And all of a sudden it went into a nosedive. I noticed the pilot trying to pull up but he was extremely low to the ground and he didn't pull up in time."
A prominent California doctor, his wife and three young children were among the crash victims.
Napa Valley ophthalmologist Dr. Erin Jacobson of St. Helena, his wife Amy and three children, Taylor, 4, Ava, 3, and Jude, 2, were on their way to see family in Bozeman, about 85 miles southeast of Butte, the Napa Valley Register reported.
"They were extraordinary, wonderful, giving and kind," Jacobson family friend Elizabeth Naylor told the Register. "Our daughters grew up together. My daughter asked [Sunday] if we could have their daughter over for a play date this week, and we told them we could after they got back."
Also on board were Vanessa and Michael Pullen of Galt, Calif., and their two children and Dr. Brent Ching, his wife Kristen, and their 2 children, from the Chico, Calif., area.
All three families knew each other from college and medical school.
The pilot has not been identified.
The aircraft had departed from Oroville, Calif., and the pilot had filed a flight plan showing a destination of Bozeman. But the pilot twice canceled his flight plan without giving a reason and headed for Butte, NTSB Acting Chairman Mark V. Rosenker said.
Rosenker said it was too early to tell the exact cause of the crash, mostly because the plane had no flight data recorder onboard.
"There are a lot of questions that still need to be answered before we can do analysis," he said.
The death toll was confirmed by Karen Byrd, a Federal Aviation Administration operations officer in Renton, Wash. Earlier, the count had been put as high as 17. Byrd said seven adults and seven children died in the crash.
The plane, a Pilatus PC-12, was believed to be taking its occupants to Montana on a ski trip. "We think that it was probably a ski trip for the kids," Fergus said.
The Pilatus PC-12's capacity is 12 adults. It was not known whether the extra people aboard was a factor in the crash, since seven of the victims were children.
Aviation expert Peter Goelz said it would be a "difficult" investigation.
"This plane does not carry a flight data recorder, so investigators are not going to have those very valuable tools to find out what was going on in the cockpit, what was going on in the plane," Goelz told FOX News.
"What's most important right now is the wreckage. Is it all there? How was the plane configured? This will be an old-fashioned investigation."
An investigator with the National Transportation Safety Board, Kristi Dunks, offered few details at a press conference in Butte Sunday night. No cause of the crash was given.
Dunks would not say if there had been a distress call from the pilot.
It was partly cloudy, the visibility was 10 miles and winds were blowing from the northwest around 10 mph at the time of the crash, according to hourly temperature information from the National Weather Service.
Butte Silver-Bow Sheriff John Walsh said there were a few people at the cemetery at the time of the crash, but no one on the ground was injured.
The plane was registered to Eagle Cap Leasing Inc. in Enterprise, Ore., Fergus said. He didn't know who was operating the plane.
I. Felkamp is listed in Oregon corporate records as Eagle Cap's president. Attempts to reach him by phone were unsuccessful.
In Switzerland, Markus Kaelin, executive assistant to the chairman of Pilatus Aircraft, said the company had no comment.
The Associated Press contributed to this report.