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Cause of Montana plane crash still a mystery

Investigators believe ice formations may have played a part in the plane crash that killed 14 Sunday in Butte, Mont., reported The Associated Press.

However, the investigators have not ruled out human error, mechanical failure, or other factors that could have lead to the plane's crashing. Investigators are also trying to answer the question of why the pilot of the aircraft changed his flight plan.

The plane crashed while descending toward Butte's Bert Mooney Airport. The plane passed through a layer of air that would have made the plane highly susceptible to ice.

Similar conditions existed when a plane crashed in Buffalo, N.Y. last month, according to safety experts.

ABC News' aviation consultant John Nance believes that the amount of passengers aboard could have contributed to the crash.

"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 to ABC News.

Nance also believes the course change could have been to allow the passengers a bathroom break.

A similar Pennsylvania plane crash occurred in 2005, with the same kind of plane and the same icy weather conditions, said Former NTSB chairman Jim Hall. (AP)