Aviation Accident Report: Aircraft crash, Butte, MT, March 22, 2009

This is a synopsis from the Safety Board’s report and does not include the Board’s rationale for the conclusions, probable cause, and safety recommendations.  Safety Board staff is currently making final revisions to the report from which the attached conclusions and safety recommendations have been extracted.  The final report and pertinent safety recommendation letters will be distributed to recommendation recipients as soon as possible.  The attached information is subject to further review and editing.

EXECUTIVE SUMMARY

On March 22, 2009, about 1432 mountain daylight time, a Pilatus PC-12/45, N128CM, was diverting to Bert Mooney Airport (BTM), Butte, Montana, when it crashed about 2,100 feet west of runway 33 at BTM. The pilot and the 13 airplane passengers were fatally injured, and the airplane was substantially damaged by impact forces and a postcrash 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. The flight departed Oroville Municipal Airport, Oroville, California, on an instrument flight rules flight plan with a destination of Gallatin Field, Bozeman, Montana. Visual meteorological conditions prevailed at the time of the accident.

CONCLUSIONS

  1. The investigation found that the pilot was properly certificated and qualified in accordance with applicable Federal regulations. The investigation also found no evidence indicating any preexisting medical or behavioral condition that might have adversely affected the pilot’s performance on the day of the accident.
  2. The investigation found that the airplane was properly certified, equipped, and maintained in accordance with Federal regulations and that the recovered components showed no evidence of any preimpact structural, engine, or system failures.
  3. The low fuel pressure state and the restricted fuel supply from the left tank during the accident flight were the result of an accumulation of ice in the fuel system with an initial concentrated amount of ice at the airframe fuel filter.
  4. If the pilot had added a fuel system icing inhibitor to the fuel for the flights on the day of the accident, as required, the ice accumulation in the fuel system would have been avoided, and a left-wing heavy fuel imbalance would not have developed.
  5. If the pilot had performed a complete preflight inspection before the flight to Oroville Municipal Airport, he would have had an opportunity to detect whether ice crystals or water were present in the fuel and determine whether the fuel filter bypass indicator was extended, which could have explained the reason for the fuel boost pump advisories annunciated during the preceding flight.
  6. About 1 hour 21 minutes into the flight, the fuel supplied to the airplane’s engine was being drawn solely from the right fuel tank by the right fuel boost pump, and the left-wing-heavy fuel imbalance continued to increase.
  7. The left and right fuel tanks were equally receiving fuel through the fuel return lines, but the left-wing-heavy fuel imbalance continued to increase during the flight because fuel was only being drawn from the right fuel tank.
  8. The fuel system continued to provide fuel to the engine throughout the flight, even with the low fuel pressure state and the degraded performance of the left-side fuel system.
  9. Although the pilot should have diverted to a nearby airport once the maximum allowable fuel imbalance had been exceeded, the pilot eventually diverted to Bert Mooney Airport likely because he recognized the magnitude of the situation and his attempts to resolve the increasing left-wing-heavy fuel imbalance had been unsuccessful.
  10. The airplane was controllable in static flight with the left-wing-heavy fuel imbalance that existed at the time of the accident, but the pilot lost control of the airplane with the dynamic maneuvers during the final moments of the flight.
  11. The large left rolling moment induced by the left-wing-heavy fuel imbalance could have been minimized or even avoided if the pilot had followed Pilatus Aircraft’s required procedures for flight operations with a fuel imbalance.
  12. 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.
  13. The pilot underestimated the seriousness of the initial fuel imbalance warnings because he had not experienced any adverse outcomes from ignoring similar previous warnings.
  14. The safety hazard involving fuel system ice accumulation could be mitigated if fuel filler placards installed aboard aircraft requiring a fuel system icing inhibitor specified that requirement.
  15. Federal Aviation Administration pilot and operator guidance on the use of fuel system icing inhibitors would help raise awareness of the need to include this additive in turbine engine-powered aircraft fuel systems that require the additive.
  16. At least four of the seven children on board the airplane were not restrained or were improperly restrained.
  17. Although the number of passengers on board the airplane during the final flight leg did not comply with the PC-12 airplane flight manual limitation requiring no more than nine passengers, the four additional passengers on board the airplane did not directly affect the outcome of the accident.
  18. For survivable accidents, passengers aboard airplanes operating under 14 Code of Federal Regulations Part 91 would be afforded better crash protection if each seat and restraint system were limited to only one passenger and children less than 2 years of age were restrained in an approved child restraint system.
  19. Although the download of nonvolatile memory data provided key information in determining the circumstances that led to this accident, a flight recorder system that captured cockpit audio, images, and parametric data would have provided additional information about the accident that was not possible to determine from the downloaded nonvolatile memory data.

PROBABLE CAUSE

The National Transportation Safety Board determines that the probable cause of this accident was (1) the pilot’s failure to ensure that a fuel system icing inhibitor was added to the fuel before the flights on the day of the accident; (2) his failure to take appropriate remedial actions after a low fuel pressure state (resulting from icing within the fuel system) and a lateral fuel imbalance developed, including diverting to a suitable airport before the fuel imbalance became extreme; and (3) a loss of control while the pilot was maneuvering the left-wing-heavy airplane near the approach end of the runway.

RECOMMENDATIONS

New Recommendations

As a result of this investigation, the National Transportation Safety Board makes the following recommendations to the Federal Aviation Administration:

  1. Amend certification requirements for aircraft requiring fuel additives, including fuel system icing inhibitors, so that those limitations are highlighted by a warning in the limitations section of the airplane flight manual. (A-11-XX)
  2. Require all existing certificated aircraft (both newly manufactured and in-service aircraft) that require fuel additives, including fuel system icing inhibitors, to have those limitations highlighted by a warning in the limitations section of the airplane flight manual. (A-11-XX)
  3. Amend aircraft certification fuel placarding requirements so that aircraft requiring fuel additives, including fuel system icing inhibitors, have a fuel filler placard that notes this limitation and refers to the airplane flight manual for specific information about the limitation. (A-11-XX)
  4. Require all existing certificated aircraft (both newly manufactured and in-service aircraft) that require fuel additives, including fuel system icing inhibitors, to have a fuel filler placard that notes this limitation and refers to the airplane flight manual for specific information about the limitation. (A-11-XX)
  5. Issue guidance on fuel system icing prevention that (1) includes pilot precautions and procedures to avoid fuel system icing problems aboard turbine engine-powered aircraft and (2) describes the possible consequences of failing to use a fuel system icing inhibitor, if required by the airplane flight manual, especially during operations at high altitudes and in cold temperatures. (A-11-XX)

As a result of this investigation, the National Transportation Safety Board makes the following recommendations to the European Aviation Safety Agency:

  1. Amend certification requirements for aircraft requiring fuel additives, including fuel system icing inhibitors, so that those limitations are highlighted by a warning in the limitations section of the airplane flight manual. (A-11-XX)
  2. Require all existing certificated aircraft (both newly manufactured and in-service aircraft) that require fuel additives, including fuel system icing inhibitors, to have those limitations highlighted by a warning in the limitations section of the airplane flight manual. (A-11-XX)
  3. Amend aircraft certification fuel placarding requirements so that aircraft requiring fuel additives, including fuel system icing inhibitors, have a fuel filler placard that notes this limitation and refers to the airplane flight manual for specific information about the limitation. (A-11-XX)
  4. Require all existing certificated aircraft (both newly manufactured and in-service aircraft) that require fuel additives, including fuel system icing inhibitors, to have a fuel filler placard that notes this limitation and refers to the airplane flight manual for specific information about the limitation. (A-11-XX)

Previously Issued Recommendations Resulting From This Accident Investigation

The National Transportation Safety Board issued the following recommendations to the Federal Aviation Administration on August 11, 2010:

Amend 14 Code of Federal Regulations Part 91 to require separate seats and restraints for every occupant. (A-10-121)

Amend 14 Code of Federal Regulations Part 91 to require each person who is less than 2 years of age to be restrained in a separate seat position by an appropriate child restraint system during takeoff, landing, and turbulence. (A-10-122)

The National Transportation Safety Board issued the following recommendation to the Federal Aviation Administration on March 18, 2010:

Establish and implement standard procedures to document and share control information, such as frequency changes, contact with pilots, and the confirmation of the receipt of weather information, at air traffic control facilities that do not currently have such a procedure. These procedures should provide visual communication of at least the control information that would be communicated by the marking and posting of paper flight-progress strips described in Federal Aviation Administration Order 7110.65, “Air Traffic Control.” (A-10-42)

Previously Issued Recommendation Classified in This Report

Safety Recommendations A-10-121, which was issued to the Federal Aviation Administration on August 11, 2010, is reclassified “Open—Unacceptable Response” in section 2.5 of this report.

Amend 14 Code of Federal Regulations Part 91 to require separate seats and restraints for every occupant.