Cessna 206 Air Ambulance Hits Obstacles During Unstabilized Approach

Casualties unknown • Villavicencio, CO

A medical evacuation flight ended in an aircraft impact with perimeter fencing during the final approach to Vanguardia Airport, resulting in one serious injury.

What happened

On November 23, 2016, a Cessna 206, registration HK2659, was operating an air ambulance mission from La Macarena to Villavicencio, Colombia. The flight was transporting a patient in critical condition along with a medical crew and an accompanying passenger.

During the final approach to Runway 05 at Vanguardia Airport, the aircraft began to descend below the recommended glide path. As the aircraft approached the runway threshold, the left horizontal stabilizer struck a post from a nearby perimeter fence. The left wing then collided with the airport's boundary mesh, dragging approximately three meters of fencing with it. The aircraft subsequently impacted the ground within the airport perimeter, approximately 60 meters from the runway threshold.

Of the five occupants on board, the pilot and two others were uninjured, and the patient survived the impact, though the patient later passed away due to pre-existing medical conditions. One nursing assistant sustained serious injuries, specifically fractures to both legs.

The investigation

The GRIAA investigation focused on the flight dynamics during the approach phase. Investigators examined the aircraft's maintenance records, which showed the Cessuna 206 was airworthy and all scheduled maintenance was up to date. The investigation also reviewed the operator's General Operations Manual and the pilot's flight performance.

Technical analysis revealed that the pilot was operating the aircraft in the "Reverse Command Region." In this aerodynamic state, which occurs at speeds below $L/D_{max}$, increasing the angle of attack to maintain altitude actually increases induced drag, requiring more power rather than less. The investigation found that the pilot failed to recognize that the low-speed approach required a significant power adjustment to maintain the descent path.

Findings

  • The pilot executed an unstabilized approach characterized by a flat, low-speed descent path below the required glide slope.
  • The pilot failed to recognize the aerodynamic implications of operating in the Reverse Command Region, specifically the need for increased power to maintain flight parameters at low speeds.
  • The pilot did not implement timely corrective measures or a go-around to avoid the obstacles located at the airport boundaries.
  • The operator's General Operations Manual lacked clear procedures regarding stabilized approach criteria and specific corrective actions for unstabilized conditions.

Probable cause

The accident was caused by inappropriate flight techniques during the final approach, where the pilot maintained an unstabilized, low-speed descent and failed to apply the necessary power increases required when operating in the reverse command region, leading to an impact with perimeter obstacles.

Frequently asked questions

What happened in the 2016-11-23 TU206G accident near Villavicencio, CO?

A medical evacuation flight ended in an aircraft impact with perimeter fencing during the final approach to Vanguardia Airport, resulting in one serious injury.

What aircraft was involved and where did it happen?

The accident on 2016-11-23 involved a TU206G, registration HK2659, at Villavicencio, CO.

What was the probable cause of the accident?

The accident was caused by inappropriate flight techniques during the final approach, where the pilot maintained an unstabilized, low-speed descent and failed to apply the necessary power increases required when operating in the reverse command region, leading to an impact with perimeter obstacles.

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