What happened
On August 21, 2015, a Bell 206B helicopter, registration TG-CHU, was conducting a flight sequence that began at La Aurora International Airport. After an initial landing in Esquipulas, the aircraft departed for its final destination in the village of Lampocoy, Zacapa.
During the approach to the landing area in Lampocoy, the aircraft began to experience a loss of lift accompanied by sudden, sharp yawing movements to the right. In an attempt to correct the uncontrolled turns, the pilot increased power (torque) while at a low altitude and low airspeed. This application of power triggered a phenomenon known as Loss of Tail Rotor Effectiveness (LTE), causing the aircraft to lose directional control and impact the ground. All occupants, including the pilot and passengers, survived the impact without injuries.
The investigation
The DGAC/UIA investigation confirmed that the aircraft was properly certified, equipped, and maintained according to Guatemalan regulations. The engine was found to be functional at the time of impact, providing power to both the main and tail rotors. Meteorological conditions at the time of the accident were suitable for visual flight.
Investigators examined the flight controls and found no mechanical blockages or obstructions in the tail rotor pedals. However, the investigation noted that an operational weight and balance document for this specific flight was not found, which was considered a contributing factor. The investigation focused on the aerodynamic interaction between the aircraft's configuration and the flight maneuvers used during the approach.
Findings
- The primary cause of the accident was the occurrence of Loss of Tail Rotor Effectiveness (LTE), an aerodynamic phenomenon that caused unexpected yawing and loss of control.
- The pilot's decision to increase torque at low altitude and airspeed to correct the yawing motion exacerbated the LTE condition.
- The pilot's approach procedure contributed to the tail rotor's inability to provide sufficient thrust to maintain directional stability.
- A lack of situational awareness prevented the pilot from recognizing the developing aerodynamic instability and implementing appropriate corrective actions.
- Potential contributing factors included pilot fatigue due to high ambient temperatures and a lack of specific experience in recognizing and recovering from LTE scenarios.
Safety action
- It is recommended that rotary-wing pilots study aircraft flight manuals and aviation publications to understand the characteristics of LTE and how to avoid it.
- Flight crews should remain vigilant regarding environmental factors such as altitude, crosswinds, and weight and balance when operating in conditions prone to LTE.
- It is recommended that pilots with private or commercial licenses undergo simulator training to practice recognizing and recovering from LTE-induced instabilities.
- The aviation authority should consider including LTE flight dynamics reviews as part of the recurrent training and license renewal processes.