The plane that crashed in Montana, killing all 14 aboard, gave no indication to air traffic controllers that the aircraft was experiencing difficulty when the pilot asked to divert to an airport in Butte, a federal safety official said Monday.

In an e-mail to The Associated Press, National Transportation Safety Board chairman Mark Rosenker said there was "no indication of any trouble when the diversion was requested to ATC (air traffic control)."

The flight was originally scheduled to fly from Oroville, Calif., to Bozeman, Mont., but after the single engine turboprop plane was en route, the pilot notified air traffic controller he was diverting to Butte.

The plane crashed Sunday afternoon just short of the Bert Mooney Airport in Butte. Like thousands of small airports across the country, the Butte airport doesn't have radar control.

National Air Traffic Controllers Association spokesman Doug Church said the NTSB has told the union they won't be a party to the crash investigation, a likely indication that investigators didn't find anything significant in the aircraft's communications with controllers. The union routinely becomes part of crash investigations unless communications between air traffic controllers and the aircraft involved are insignificant.