Accident Overview
On May 21, 2018, at approximately 0845 mountain standard time, an experimental, amateur-built MTO Sport gyroplane (registration N574BR) was substantially damaged during an accident near San Manuel Airport (E77) in San Manuel, Arizona. The flight instructor and student pilot on board were not injured. The flight was being conducted as a local familiarization flight under Title 14 Code of Federal Regulations Part 91.
Flight and Incident Sequence
The instructor reported that after an uneventful takeoff, when the gyroplane reached about 400 ft above ground level, she heard a loud bang. This was followed by severe vibrations and a total loss of engine power. She executed a right turn back toward the runway and successfully performed a power-off landing. During the landing roll, flames were observed emanating from the rear of the gyroplane. After the aircraft came to a stop, both occupants egressed safely, and the fire was subsequently extinguished.
Examination Findings
Post-accident examination revealed that one propeller blade and part of the propeller hub were missing. The gyroplane exhibited extensive vibration-related damage. One of the remaining propeller blades had struck a rotor blade. A fuel line was found damaged and open, and the fuselage and horizontal stabilizer had sustained structural damage. The muffler, coolant line, and both carburetors were either fracture-separated or shaken loose.
Propeller Failure Analysis
Examination of the fractured propeller hub showed that it had failed due to fatigue cracking. The cracks originated at a network of corrosion pits along the surface of the propeller blade root seat. A similar large crack was present in a second propeller blade root seat. The fracture surface displayed ratchet marks, indicating multiple crack initiation sites, as well as crack arrest marks and finely spaced fatigue striations consistent with high-cycle fatigue from repeated high-rpm propeller loads. Analysis of the corrosion pits found elements consistent with common salts.
The propeller blade itself was fractured in two locations. A longitudinal fracture ran between composite plies, alternating between different layers. A transverse fracture exhibited fiber pullout and fractures at multiple heights, with a central metallic tube that had buckled and collapsed. The internal tube had a rough surface texture and a 45° slant orientation. Adjacent tube material had thinned and showed deformation in multiple locations. The periphery of the angled root seat had chatter marks on the blade root.