What happened
On May 14, 2012, a Safari helicopter, registration N 557XS, was conducting a test flight near the Hosín airfield (LKHS) to verify the aircraft's performance following recent maintenance intended to reduce vibrations. The flight, which included the pilot and one observer, proceeded normally through the airfield area before the pilot departed toward the southwest.
While flying at approximately 50 meters AGL near the town of České Budojovice, the aircraft experienced a sudden and violent change in flight characteristics. Witnesses observed a dark object falling from the helicopter, followed immediately by the aircraft pitching forward and entering a steep, uncontrolled descent. The helicopter struck the ground in a wooded area near Litvínovice - Šindlovy Dvory, where the impact and subsequent fire destroyed the aircraft. Both occupants sustained fatal injuries.
The investigation
The ÚZPLN investigation focused on the sequence of events leading to the loss of control and the mechanical state of the aircraft. Investigators examined the wreckage and interviewed witnesses who observed the aircraft's behavior and the separation of an object from the airframe. The investigation also reviewed the aircraft's maintenance history, noting that while the engine remained functional until impact, the aircraft's airworthiness certificate had expired.
Findings
- The investigation established that the aircraft was likely carrying a portable ballast weight used for longitudinal balance when only one occupant is on board.
- A critical failure occurred when the loss of the ballast weight caused an immediate shift in the aircraft's center of gravity, forcing the pilot to make sudden, energetic control inputs to maintain flight.
- These intense maneuvers caused the main rotor blade to strike the tail boom structure.
- The impact of the rotor blade severed the tail rotor drive shaft and damaged the tail rotor pitch control system, rendering the helicopter uncontrollable.
- The loss of structural integrity caused extreme vibrations, leading to the separation of various components, including the cockpit canopy, during the descent.
- The aircraft's annual inspection by an authorized FAA mechanic had not been performed, and the aircraft was not in a condition for flight.
Safety action
Based on the high probability that the ballast weight was lost due to a failure in the primary retaining mechanism, it is recommended that the manufacturer revise the design of the ballast weight securing method or the construction of the retaining pin to prevent accidental separation.