What happened
While traveling to collect a medical patient, an aircraft experienced an in-flight breakup while operating on the leeward side of the Sierra Nevada mountains. At the time of the accident, lenticular clouds had been noted in the vicinity. The flight crew, consisting of the pilot and a flight nurse, were operating in an area where other pilots had recently reported significant airspeed fluctuations, ranging from 60 knots above to 40 knots below normal speeds. An advisory for moderate turbulence was active during the flight, though a SIGMET for severe turbulence was not issued by the weather service until approximately one hour after the accident occurred.
Findings
Investigations revealed that the aircraft's structure failed after encountering turbulence that surpassed its design limits. There was no evidence to suggest that the pilot had requested a weather briefing from flight service or other vendors before the flight began. The accident resulted in two fatalities.