On June 1, 2023, about 1000 mountain daylight time, an experimental, amateur-built MTO Sport gyroplane, N207AG, was substantially damaged when it was involved in an accident near Gardiner, Montana. The pilot received minor injuries. The gyroplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that, before the accident, he performed two takeoffs and two landings, then departed for a short local flight. When he returned, he performed an approach to land on runway 10. After the touchdown on the runway, while at a forward speed of about 10 mph, the gyroplane suddenly yawed to the right, despite the pilot’s application of full left rudder and nosewheel steering. The gyroplane then rolled to the left and the rotors contacted the runway, which substantially damaged the rotor mast. The pilot, who was seated in the front seat, received minor injuries. The gyroplane came to rest on its right side, off the left side of the runway. All major components remained attached to the airframe, except for a segment of one rotor blade. Postaccident examination revealed the left side of the metal mechanical stop for the nosewheel was bent downward, and the nosewheel was turned right, beyond the mechanical stop limit. Three of the four control rods that provide rudder movement and nosewheel steering had fractured and separated from their respective rod end bearings, as shown in figure 1. No preimpact mechanical malfunctions or anomalies were observed that would have precluded normal operation.

Figure 1. Image showing the nosewheel displaced to the right beyond the mechanical stop limit, the two partially separated front seat rudder/nosewheel control rods, and the back seat, left-side control rod. (Source: FAA) Further examination of the control rods revealed that each control rod separated through the threaded end of one of the rod end bearings. The separations occurred through one of the top threads whose thread root was inline with the top of the mating nut. The macro shapes of the separations were cup-and-cone, which is consistent with overstress. The fracture surface for the longest control rod had intergranular features consistent with tensile overstress, possibly due to low toughness. The fracture surfaces on the other two control rods had features consistent with ductile tensile overstress. The gyroplane was a two-seat model with flight controls installed for both seats. According to the manufacturer, “The rear rudder pedals are connected to the rudder via steel cables, and to the front pedals by linkages [control rods] via the nosewheel for steering. Pushing the right pedal will turn the aircraft right in the air and right when on the ground.” Figure 2 is an excerpt from the manufacturer’s maintenance manual and details how the design controlled both the rudder and the nosewheel steering.

Figure 2. Excerpt from the manufacturer’s maintenance manual, showing pedals, control rods, and cables that control the rudder and nosewheel steering. (Source: Manufacturer) According to the manufacturer, the nosewheel limit stop withstands the pedal forces and butts up against the center keel tube of the gyroplane. The design was built to BCAR Section T, “Light Gyroplanes” standards. According to the manufacturer, normal pilot inputs will not bend the stop. A visual examination of the mechanical stop revealed the left-side stop was bent downward, which allowed the nosewheel to travel beyond its mechanical limit. The closest weather reporting facility was Billings Logan International Airport (BIL), Billings, Montana. An automated weather report around the time of the accident recorded wind variable at 5 knots, 10 statute miles visibility, few clouds at 6,500 ft, few clouds at 10,000 ft, scattered clouds at 24,000 ft, temperature 24°C, dew point 11°C. The pilot reported the weather as fair and calm. According to a Gardiner Airport website, the runway conditions were described as “asphalt/aggregate friction seal coat, in poor condition. LARGE CRACKS AND VEGETATION GROWTH THROUGHOUT RUNWAY SURFACE.”