What happened
On February 14, 2013, a Bell 206B3 helicopter, registration HK-2887, was performing a non-scheduled commercial transport flight for the Colombian National Army. The flight originated from Popayán, carrying one pilot and three passengers, destined for a National Police base in the urban area of Caldono, Cauca.
During the final approach to the landing site—a cleared area near a local police station—the pilot performed a low-altitude reconnaissance at approximately 100 feet to assess wind conditions. Using a smoke grenade to observe wind direction, the pilot determined the wind was calm. However, as the aircraft continued its final approach on a heading of approximately 1 .37°, it encountered a sudden and unexpected shift in wind direction.
This shift resulted in an inadvertent tailwind during the last third of the approach. At an altitude of approximately 30 feet and a speed below 13 knots (below effective translational lift), the aircraft experienced a continuous rightward yaw that could not be corrected with left pedal input. The helicopter entered a 360-degree right-hand turn and a rapid vertical descent, impacting the terrain near the intended landing zone.
The investigation
The GRIAA investigation focused on the aerodynamic conditions at the time of the accident and the environmental constraints of the landing site. Investigators analyzed the flight path, the pilot's actions during the reconnaissance phase, and the wind patterns in the region. The investigation established that the landing area, located in the Central Cordillera, is subject to significant mountain wind effects due to the abrupt relief of the terrain.
Furthermore, the investigation noted that the landing site was a confined area with significant approach limitations caused by both physical obstacles and security concerns related to local irregular groups, which restricted the available approach paths. The investigation also reviewed the aircraft's maintenance history and the pilot's flight experience, finding no mechanical failures or pilot incapacitation as contributing factors.
Findings
- The primary cause of the accident was the loss of tail rotor effectiveness (LTE) triggered by an unexpected wind shift into a tailwind condition during the final approach.
- The aircraft was operating at a low airspeed (below 13 knots), which placed it within the critical wind azimuth range for the Bell 206B3.
- The sudden change in wind direction caused an uncontrollable rightward yaw and a subsequent vertical impact.
- The landing site's geography and the presence of obstacles limited the pilot's ability to execute alternative approach trajectories.
- The impact resulted in one serious injury (the pilot, who suffered a spinal fracture) and three minor injuries among the passengers.
- The aircraft sustained major structural damage, including broken main and tail rotor blades, severe transmission damage, and fuselage fractures.