from National Transportation Safety Board

12/1/2011 - BUTTE, Mont.  -- Nearly two and a half years after they began their investigation into a plane crash that killed 13 members of a family bound for a Montana ski resort, National Transportation Safety Board officials say they have cracked the case.

In July the board announced that the cause of the March 2009 deadly crash of the Pilatus PC-12 aircraft was a series of operational errors made by the pilot, 65-year-old Ellison Summerfield, who also died in the crash.

According to the report, the pilot failed to ensure that a fuel system icing inhibitor was added to the fuel prior to the mishap flight, which ultimately led to ice blocking fuel in the left wing. The pilot also failed to take appropriate remedial actions, including diverting to a suitable airport, after the airplane warning systems indicated a low-fuel pressure state that ultimately resulted in a significant lateral fuel imbalance. And, the pilot lost control while maneuvering the left-wing-heavy airplane near the approach end of the runway.

"The pilot's pattern of poor decision making set in motion a series of events that culminated in the deadly crash," said NTSB Chairman Deborah A.P. Hersman. "Humans will make mistakes, but that is why following procedures, using checklists and always ensuring that a safety margin exists are so essential -- aviation is not forgiving when it comes to errors."

On March 22, 2009, at about 2:32 p.m., the Pilatus airplane crashed about 2,100 feet west of runway 33 at Bert Mooney Airport in Butte, Mont. The flight departed Oroville Municipal Airport in Oroville, Calif., en route to Gallatin Field in Bozeman, Mont., but the pilot diverted to Butte for unknown reasons. The pilot and the 13 passengers, who were related to aircraft owner Irving Feldcamp, were fatally injured, and the aircraft was substantially damaged by impact forces and a post-crash fire.

The Pilatus flight manual states that a fuel system icing inhibitor must be used for all flight operations in ambient temperatures below 0 degrees Celsius to prevent ice formation in the fuel system, investigators said. The board concluded that the airplane experienced icing in the fuel system which resulted in a left-wing-heavy fuel imbalance.

The increasing fuel level in the left tank and the depletion of the fuel from the right tank should have been apparent to the pilot because that information was presented on the fuel quantity indicator, investigators said. This should have prompted the pilot to divert the airplane to an airport earlier in the flight as specified by the airplane manufacturer.

"If the pilot had diverted earlier in the flight to one of several suitable airports along the airplane's route of flight, the outcome of this flight would likely have been different because the airplane would have had a less severe fuel imbalance and the pilot would not have had to contend with the airplane's deteriorating performance as the imbalance steadily progressed," the report said.

While investigators say they don't believe it directly affected the outcome of the crash, they noted that the PC-12 is only equipped to carry nine passengers. That means it was transporting four more people than should have been allowed -- just another example of the pilot bending the rules. Investigators also said at least four of the seven children on board the airplane were not restrained or were improperly restrained.

Because there was no crash-proof flight recorder in the aircraft, it took longer for investigators to discover what happened. They were able to salvage some tiny microchips from the plane's heavily damaged safety-warning system. Information from those microchips helped them solve the case.