BUTTE, Mont. ” Investigators said Monday they’ll look into whether the single-engine turboprop plane was overloaded when it nose-dived into a cemetery and killed all 14 people on board.

“It will take us a while to understand,” Mark Rosenker, acting chairman of the National Transportation Safety Board, said at a news conference. “We have to get the weights of all the passengers, we have to get the weight of the fuel, all of the luggage.”

The plane was likely designed to carry a total of 11 people from Oroville, Calif, including two pilots, Rosenker said at a news conference. Oroville is about two hours from Truckee and Lake Tahoe.

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Making the case more complicated, federal aviation officials said the plane didn’t have a cockpit voice recorder or flight data recorder and wasn’t certified to carry commercial passengers.

The turboprop plane left Oroville, Calif., headed for Bozeman, Mont., but changed course to Butte, where it crashed on final approach Sunday. The pilot gave no indication to air traffic controllers that the aircraft was experiencing difficulty when the pilot asked to divert to an airport in Butte, Rosenker said in an e-mail earlier in the day.

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Rosenker said there was “no indication of any trouble when the diversion was requested to ATC (air traffic control).”

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.