What happened
On October 10, 2018, at approximately 8:10 a.m., a Bell OH-58A helicopter, registration HI-997, was conducting agricultural spraying operations in Palo Verde, Montecristi, Dominican Republic. While the pilot was returning to a refueling point at a speed of approximately 80 knots, a loud noise and a sudden, abrupt pitch occurred.
Following the sudden movement, the pilot performed a controlled emergency landing in a rice cultivation field from an altitude of roughly 350 feet. Upon coming to a halt, the pilot discovered that the tail rotor and its associated transmission had separated from the aircraft during flight.
The investigation
The CIAA investigation focused on the structural integrity of the tail rotor system and the sequence of mechanical failures. Investigators examined the wreckage of the tail boom and the recovered components. The investigation located the tail transmission approximately 750 meters away from the aircraft's final resting position.
Physical examination of the tail rotor blade grips revealed that one blade (identified as the red blade) had detached in flight. The inspection of the second blade (the white blade) showed evidence of breakage due to impact, likely occurring when the component struck the ground. The investigation also reviewed the pilot's commercial license, medical certification, and the aircraft's maintenance records, which showed a recent annual inspection completed in September 2018.
Findings
- The primary cause of the accident was the in-flight separation of one tail rotor blade.
- The resulting imbalance created severe vibrations, which caused the mounting bolts of the tail transmission to fail, leading to the transmission detaching from the tail boom.
- The pilot was the sole occupant and remained uninjured during the event.
- The aircraft sustained severe damage, specifically concentrated on the tail boom structure.
- The tail rotor blades were not recovered at the scene.