The board says the crew did not declare an emergency and the aircraft dropped from an altitude of 2,400 metres to about 900 metres in less than 20 seconds.
It says this evidence — combined with the wreckage dispersal and the lack of terrain damage — is consistent with in-flight break-up.
The board says the investigators will remove the wreckage and take it to a TSB facility where a detailed examination will be conducted.
Data will also be collected from various sources, including the aircraft manufacturer, Transport Canada, Nav Canada, Environment Canada and the operator.
The bodies of the two pilots, 34-year-old Robert Brandt and 32-year-old Kevin Wang, were found along with the wreckage of the Carson Air flight Tuesday morning.