What happened
On 19 November 2019, a ZEN1 gyroplane, registration OM-M393, was conducting a training flight at EPNC, Poland. The crew, consisting of an instructor and a student, performed a "touch and go" maneuver at approximately 12:05 LMT. During a steep climb at an altitude of roughly 20 to 30 meters AGL, one of the main rotor blades separated from the aircraft.
The separation caused the remaining blade to become dynamically unbalanced, leading it to collide with the aircraft's fuselage, tail, and propeller. This impact caused multiple components to detach from the aircraft. The gyroplane lost all rotor function and fell almost vertically onto the grass runway. The impact unsealed the fuel tanks, causing the wreckage to burst into flames. While the instructor was found outside the aircraft and briefly received resuscitation attempts, both the instructor and the student sustained fatal injuries.
The investigation
The PKBWL investigation examined the aircraft's maintenance history, the flight sequence, and the structural integrity of the rotor assembly. Investigators noted that the instructor had been performing intensive flight training and had recently performed maintenance work on the rotor using wrenches shortly before the flight. The investigation also reviewed the mechanical properties of the aluminum-magnesium alloy used in the blades and the design of the rotor blade connector.
Findings
- The primary cause of the accident was the inflight separation of one of the main rotor blades.
- The rotor blade separation was characterized by a two-phase crack, though no specific material defects were found.
- The design of the rotor blade connector contributed to stress concentrations within the assembly, which negatively impacts fatigue durability.
- Maintenance errors were a factor, specifically that tightening torques for the blade bolts were inconsistent.
- The instructor did not perform a pre-flight inspection on the day of the accident.
- The operation of the main rotor blades had an unknown duration of use.
- The instructor had previously noted vibrations in the aircraft at certain speeds but did not address them through formal inspection.
Safety action
Following the investigation, the PKBWL issued recommendations for the manufacturer to implement design changes to the hub to reduce the bending moment acting on the blades. Additionally, the Civil Aviation Authority issued an Airworthiness Directive to limit the service life of duralumin main rotor blades manufactured by Aviation Artur Trendak and Cellier Aviation to 1,000 flight hours until design improvements are implemented.