What happened
A cargo flight involving a twin-piston-engine aircraft departed from an outlying airport with a planned stop at an intermediate destination before reaching its final base. The flight was conducted under visual flight rules (VFR) following a brief consultation with company dispatch personnel. However, weather conditions at the intermediate destination included low cloud ceilings and terrain that likely required an instrument approach, which the aircraft was not equipped to perform. During the flight, the aircraft transitioned from daylight into darkness, complicating the pilot's ability to navigate the mountainous landscape without GPS or terrain mapping tools.
Radar data showed the aircraft initially followed its intended path but then entered a series of maneuvers involving various climbs and descents. After a period of being obscured by high terrain, the aircraft reappeared on radar and subsequently requested an instrument flight rules (IFR) clearance. The pilot requested a descent to 10,000 feet to avoid heavy turbulence, but air traffic control (ATC) could only authorize a descent to the minimum vectoring altitude of 9,700 feet. Shortly after reaching 10,000 feet, radar contact was lost. The aircraft subsequently struck the terrain in a steep, near-vertical, nose-down trajectory, resulting in 0 survivors.
Findings
Investigation into the crash revealed that the aircraft encountered significant meteorological hazards, including supercooled large droplets (SLD) and intense mountain-wave activity. The aircraft was subjected to powerful up-and-down drafts, with the final radar contact occurring within a downdraft of 600 to 1,000 feet per minute. The encounter with airframe icing and strong up-and down-drafts likely compromised the aircraft's aerodynamic stability and controllability.
Several contributing factors were identified:
- The descent to 10,000 feet placed the aircraft in a layer of clouds containing icing conditions and severe vertical air movements.
- The pilot may have been susceptible to reduced mental acuity due to a potential lack of supplemental oxygen during high-altitude flight segments.
- There was a possibility of improper pitot heat management, which could have led to unreliable airspeed indications.
- The accumulation of ice, combined with the physical strain of maneuvering through intense turbulence, may have led to an aerodynamic stall or loss of control.