What happened
On 25 July 2005, a Canadian Safari helicopter, which was not registered and lacked an airworthiness certificate, was performing a local flight near an unlicensed ultralight field in Cobreces, Cantabria. The flight was being conducted to adjust flight controls and address vibrations noted during previous maneuvers.
While flying at an altitude below 300 feet during the return to the airfield, the aircraft experienced a sudden, intense turn to the left. The occupants felt a "tail shudder" before the helicopter began spinning uncontrollably about its vertical axis. The aircraft subsequently spiraled erratically and impacted a corn field, coming to rest on its left side. The impact was severe, resulting in 1 fatality and 1 serious injury.
The investigation
The CIAIAC investigation focused on the mechanical integrity of the tail rotor assembly. Investigators examined the wreckage and performed laboratory testing on the detached components. The examination of the tail rotor assembly revealed that the tail rotor blades had detached in flight.
Technical analysis of the components showed that the tail rotor spindle had been mounted in an orientation that was 9/0° out of alignment with the correct assembly instructions. This improper installation was possible because the component's design allowed it to be mounted in two different positions without any physical indication of the correct orientation. Testing confirmed that this incorrect mounting led to excessive loads on the internal components.
Findings
- The primary cause of the accident was the fatigue failure of the delta pin that connects the spindle to the tail rotor driveshaft. This failure subsequently caused the spindle arm to break and the tail rotor blades to detach.
- The tail rotor spindle had been incorrectly mounted at some point during the aircraft's operational history.
- The design of the spindle assembly allowed for incorrect installation because it lacked any marking or physical feature to distinguish the correct side.
- The aircraft was being operated by individuals without pilot licenses, and the helicopter had not been registered or inspected by the Spanish Civil Aviation Authority.
- The lack of regulatory oversight regarding the aircraft's assembly and maintenance contributed to the undetected improper assembly of the tail rotor components.