A preliminary report on the Montana plane crash that killed 14 people two weeks ago says the Bay Area pilot twice asked air traffic controllers to divert from the flight's original destination but gave no reason either time.
The National Transportation Safety Board's report was released Thursday. It said an eye witness told investigators he saw the single engine turboprop west of the runway centerline at the Bert Mooney Airport in Butte, Mont., when the aircraft banked to the left and flew farther west of the runway, then it rolled, pitched down and descended out of view.
The report said the pilot of the Pilatus PC-12/45 twice asked air traffic controllers for permission to divert from the flight's original destination of Bozeman to Butte.
Also under scrutiny are weather conditions that could have caused icing on the plane's wings and possible overloading. The plane was configured to seat just 10 people, but the fact that several of the 14 passengers were small children has dampened speculation that excess weight was a factor.
The investigation has been hampered by the lack of a cockpit voice recorder or data recorder, which were not required on the private flight. Rosenker said his agency may subpoena cell phone records of the victims to see if they could provide further clues.
Most of the wreckage was confined to a small area, consistent with witness reports that the plane nose-dived straight into the ground.
While descending toward Butte's Bert Mooney Airport, the plane passed through a layer of air at about 1,500 feet that was conducive to icing because the temperature was below freezing and the air "had 100 percent relative humidity or was saturated," according to AccuWeather, a forecasting service in State College, Pa.
Safety experts said similar icing conditions existed when a Continental Airlines twin-engine turboprop crashed into a home near Buffalo Niagara International Airport last month, killing 50.
Since 2001, federal authorities have investigated 15 crashes involving PC-12's. Six involved fatalities, with a total of 14 killed prior to Sunday's crash. About 800 PC-12s are in service in the U.S.
Former NTSB chairman Jim Hall said there were similarities between the Montana crash and a 2005 crash near Bellefonte, Pa., that killed a pilot and five passengers. The plane in both cases was a Pilatus PC 12/45, and in both there were reports of conditions conducive to icing at lower elevations and witness reports that the plane appeared to dive into the ground.