Accident Investigation at Its Finest

By John DeLisi

Pilatus PC-12
Pilatus PC-12

On March 22, 2009, a Pilatus PC-12 bound for Bozeman, Montana, diverted to Butte’s Bert Mooney Airport and crashed short of the runway. The pilot and all 13 passengers were killed and the airplane was almost entirely damaged from the impact and post-crash fire.

Last week, the NTSB Board met and determined the probable cause of this accident was a series of operational errors made by the pilot, notably the failure to add fuel system icing inhibitor to the fuel prior to the accident flight.

Uncovering the cause of this tragic accident was a major challenge for our investigative team. There were no survivors, no flight data recorders, no documented distress calls, and completely destroyed airplane wreckage. There was little to go on. For months, our team was uncertain whether they would be able to solve this puzzle.

There’s an expression “leave no stone unturned.” That is exactly what Dennis Diaz, this investigation’s systems group chairman, did. He methodically sifted through the wreckage to find a small circuit board because he believed one of its tiny computer chips could provide investigators much-needed information. He was right.

Finding the small computer chip that could rest on Dennis’s fingertip among the airplane wreckage was truly like finding a needle in a haystack.

That was just the first step. The circuit board was badly damaged and there were doubts the chip could be read. Dennis learned that even the company that manufactured the board would have difficulty with one so badly damaged. Undeterred, he worked with the Swiss Aircraft Accident Investigation Bureau and Germany’s Federal Bureau of Aircraft Accident Investigation. With a bit of luck and lots of ingenuity, intelligence, and talent, crucial data was extracted to illuminate a path to determine the accident’s cause.

The tiny computer chip provided huge pieces of information about the functioning of the fuel system onboard the airplane. Dennis Diaz’s investigative work was among the best I’ve seen in my 20-plus years of investigating aviation accidents.

Thanks to the extraordinary efforts of Dennis and the entire investigative team, the NTSB was able to determine the probable cause of the accident. This led to issuing important safety recommendations to help prevent future accidents and, just as importantly, to providing an answer to the family and friends of those who lost their lives in this tragic accident.


John DeLisi is Deputy Director of the Office of Aviation Safety.

One thought on “Accident Investigation at Its Finest”

  1. I’ve been amazed & pleased about the lengths that the NTSB & its teams goes to in investigating accidents. I’ve looked at the NTSB published Reports, and they really dig deep. From my personal aviation & pipeline knowledge viewpoint, transportation is safer from their efforts.

    In this case, it was lack of fuel system icing inhibitor as the cause. But, for example, what if the accident had been caused a design flaw in the fuel system that needed immediate repairs on all of this type of aircraft, but no one spent the time to find the flaw? Writing off the cause of an accident as “unknown” leaves the door open to future accidents of the same type.

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