What happened
On 4 December 2016, a Beechcraft E9/90, registration N-79CT, departed from Cuatro Vientos aerodrome in Spain, bound for Cascais, Portugal. The flight was intended to facilitate repairs to a weather radar at a maintenance center. Due to adverse weather and instrument meteorological conditions (IMC) at the departure airfield, the takeoff was delayed until late afternoon.
While climbing toward its assigned cruise level of FL210, the aircraft experienced a sudden left yaw. Radar data indicates that the aircraft began a rapid descent, with airspeed dropping significantly until the aircraft reached a stall. This triggered a spin that eventually transitioned into a flat spin. During the uncontrolled descent, the aerodynamic loads placed on the horizontal stabilizer exceeded its design limits, causing the tail section to break into five separate pieces in flight. The aircraft subsequently impacted the ground and was destroyed by the impact and a post-crash fire. All four occupants were killed.
The investigation
The CIAIAC investigation analyzed radar tracks from the Valladolid and Valdespina stations, which provided critical data on the aircraft's flight path, speed, and heading. The investigation examined the aircraft's structural failure, the meteorological conditions along the route, and the pilot's qualifications. Investigators also reviewed the aircraft's maintenance status, noting that the weather radar was non-operational at the time of the flight. The analysis of the wreckage and the high degree of destruction prevented a precise determination of the exact sequence of events leading to the initial stall.
Findings
- The primary cause of the accident was the loss of control of the aircraft in flight due to a stall and subsequent spin.
- The pilot elected to proceed with the flight despite adverse IMC conditions and a non-functional weather radar.
- Forecasts of moderate to strong icing conditions, including cumulonimbus clouds with temperatures as low as -19°C, suggest that ice accumulation may have contributed to the loss of control.
- The use of the autopilot, and the failure to disengage it during the emergency, likely contributed to the accident.
- The pilot lacked the required type rating for the Beechcraft E90 and had inadequate training for managing abnormal or emergency situations in this specific aircraft type.