Investigators said ice may have been one of the factors behind this weekend's plane crash in Montana that left 14 people dead but warned Tuesday that the real cause could take a long time to determine.
Conditions at the time were ideal for ice, meteorologists said, just as in last month's crash of a Continental Airlines commuter plane near Buffalo, N.Y., that killed 50.
National Transportation Safety Board officials have said ice is one possible cause in the Buffalo crash, which is still under investigation.
But unlike the Buffalo crash, there were no flight data or voice recorders onboard the plane -- a Pilatus PC-12, high-end, single-engine turbo prop -- that could help pinpoint a cause.
The weather conditions were conducive to ice formation in the Montana crash, which is one of the two key suspected causes, former National Transportation Safety Board official John Goglia told ABC News. He added that the way the Pilatus nose-dived into the ground was similar to the way the Continental plane crashed in Buffalo.
Another key factor investigators are looking at is weight, or a shift in weight. The multimillion dollar Pilatus was carrying more passengers than it was licensed for, officials said Monday, and they will investigate whether carrying four extra passengers contributed to the crash.
But seven of the 14 passengers were children varying in age from 1 to 9, so it's not clear if weight was a factor. But balance or a sudden shift in weight could be a contributing cause.
ABC News' aviation consultant John Nance said the Pilatus PC-12 is a good, resilient aircraft but that extra people on this type of a plane could create not only a possible weight problem but a balance problem too.
"I'm convinced, even at this early stage, that one of the areas they need to look at the closest is weight and balance," Nance said.
Nance speculated that if people were moving around, the aircraft's center of gravity could have fatally shifted, making it next to impossible for the pilot to control, especially on approach.
"The fact that you've got children onboard, they may see something out of the airplane at the last minute. People unstrap their seat belts, get up and move, and your center of gravity could shift," Nance said. "When you overstuff a number of people on an airplane, you have the potential for getting it outside what we call the envelope of the center of gravity."
Mark Rosenker, acting chairman of the NTSB, said Monday that the agency would calculate the weight of the luggage, fuel and passengers.
"Lap children can be allowed on an aircraft up to the age of 2," Rosenker said. "We can't tell you if in fact they were sitting on the laps or not."
Investigators said they have no reason to believe the plane ran out of fuel or had mechanical problems.
Rosenker emphasized at a briefing Monday that there is unlikely to be a quick answer as to what caused the fatal crash.
"This will be a long and tedious investigation, extremely thorough," Rosenker said. "We will look at every factor which could affect the performance of this aircraft."
On Tuesday, the AOPA Air Safety Foundation -- an aviation association -- cautioned against jumping to conclusions in the fatal accident.
"It's important to remember that except for the extremely rare single-point catastrophic failure, aviation accidents are almost invariably the result of a chain of events and decisions," said Air Safety Foundation President Bruce Landsberg. "The National Transportation Safety Board is extremely good at accident reconstruction, but it will take them months to find and then unravel all the links in this accident's chain."
The plane was flying from Oroville, Calif., Sunday morning on a 2½ hour flight to Bozeman, Mont. But instead of reaching its final destination, the plane diverted to Butte -- about 85 miles northwest of Bozeman -- where it nose-dived into a cemetery 500 feet short of the runway at the Bert Mooney Airport, bursting into flames and killing all 14 people onboard.
Jim Hall, former NTSB chairman, pointed to similarities between the Montana crash and a 2005 crash near Bellefonte, Pa., which also involved a Pilatus PC 12/45 and killed the pilot and five passengers.
In both disasters, there were reports of conditions conducive to icing at lower elevations and reports from witnesses that the plane appeared to dive into the ground.
There was no emergency radio call made by the pilot, identified as Buddy Summerfield, 65, of Redlands, Calif. Summerfield was a former military flier who had logged 2,000 hours flying the Pilatus PC-12, according to federal officials.
And it remains unclear whether an emergency situation, or just a last minute change of plans, prompted the pilot to divert to Butte.
The owner of the plane, Dr. Bud Feldkamp, was not onboard but lost two daughters, two son-in-laws and five grandchildren in the crash.
It is unknown why the pilot changed course to Butte. Nance said the decision could simply have been made to give passengers a bathroom break.
Witnesses who saw the plane overhead immediately knew something was terribly wrong.
"I heard the engine, and I look up to see it spinning and going into a nose dive," Kenny Gulick, who witnessed the crash, told "Good Morning America." "It was spinning. Normally, it would be at 90 degrees. It was at 180 degrees. ... The pitch of the nose tried to move up slowly, but it was too close to the ground."
The passengers onboard were longtime friends from California. The four families were bound for a weekend ski vacation in Montana with their young children.
Butte residents Steve and Martha Guidoni and her husband raced to the scene when they witnessed the plane spiral down. Moments later, it crashed straight into the ground.
"It came in the wrong angle and it was pretty low and then it was like something stopped midair, and it went boom," Martha Guidoni told ABC News. "I could not fathom seeing what I've seen. I just kept telling him, it's too unreal to be real. ... It looked like a meteorite hit the ground. ... I've never seen anything so scary in my life."
The plane crash left a 10-foot deep crater at the cemetery. At the fiery wreckage, Steve hoped he would find a miracle, but he didn't see it.
The single-engine plane was manufactured in 2001 and owned by Eagle Cap Leasing Inc., based in Enterprise, Ore.
The last fatal plane crash that occurred was in February, when a Continental Airlines plane fell on a house in a suburb of Buffalo, N.Y., killing all 49 passengers onboard.
ABC News' Lisa Fletcher contributed to this report.