The National Transportation Safety Board determined today that the cause of the March 2009 deadly crash of a Pilatus airplane was a series of operational errors made by the pilot. The pilot failed to ensure that a fuel system icing inhibitor (FSII), commonly referenced by the brand name "Prist", was added to the fuel prior to the accident flight. 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 pm (MDT), a Pilatus PC-12/45, N128CM, crashed about 2,100 feet west of runway 33 at Bert Mooney Airport (BTM) in Butte, Montana. The flight departed Oroville Municipal Airport in Oroville, California, en route to Gallatin Field in Bozeman, Montana but the pilot diverted to Butte for unknown reasons. The pilot and the 13 passengers were fatally injured and the aircraft was substantially damaged by impact forces and a post-crash fire. The airplane was owned by Eagle Cap Leasing of Enterprise, Oregon, and was operating as a personal flight under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed at the time of the accident.
During the investigation, the NTSB determined that the pilot did not add a fuel system icing inhibitor when the airplane was fueled on the day of the accident. 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. The NTSB 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. This should have prompted the pilot to divert the airplane to an airport earlier in the flight as specified by the airplane manufacturer.
The NTSB issued recommendations to the Federal Aviation Administration and the European Aviation Safety Agency, to require fuel filler placards and guidance on fuel system icing prevention.
A synopsis of the NTSB report, including the probable cause, findings, and safety recommendations, is available on the NTSB website.
The full report will be available on the website in several weeks.