The experimental amateur-built gyroplane crashed during an instructional flight in clear daylight with low winds. Witnesses observed and heard the gyroplane flying around the local area. One witness estimated that the gyroplane was operating at an airspeed of 20 to 30 knots, about 1,000 ft above ground level. Witnesses also heard additional noises coming from the gyroplane described as banging, whining, and the engine stopping. Some observed debris and objects fall from the sky, with some witnesses describing the loss of propellers, and/or rotor blades. They further described that the gyroplane did not autorotate, but descended rapidly, and was observed to spin, pitch over, tumble, and descend inverted. After impact, smoke and fire was also observed.Postaccident examination of the wreckage did not reveal evidence of any preimpact malfunctions or failures that would have precluded normal operation. Metallurgical examination of a rotor blade that was found at a distance from the accident site revealed the blade had broken off as a result of overstress, which resulted in separation of the rotor blade outboard of the blade grip.Examination of the wreckage also revealed that one or both of the rotor blades came into contact with the propeller and vertical stabilizer as both teeter stops (droop stops) were bent in a downward direction. A black witness mark on one of the rotor blades corresponded to the location of the propeller, which had two of its three blades broken off, and a blue paint transfer was present that corresponded to the position of the vertical stabilizer. The contact likely occurred as a result of the rotor being unloaded by the flying pilot, which would have triggered a rapid decay in rotor speed. The decay in rotor speed likely resulted in a loss of rotor stability or flap, which could have resulted in the gyroplane pitching forward and tumbling as was reported by witnesses. Page 2 of 11 ERA22FA344The investigation could not determine which pilot was flying at the time of the accident. Review of logbooks indicated that the flight instructor had provided the pilot under instruction about 9 hours of instruction in the gyroplane before the accident. Toxicological tests revealed both pilots tested positive for ethanol in liver tissue specimens. However, each pilot also had another liver tissue specimen and a brain tissue specimen test negative for ethanol, indicating that the detected ethanol likely was from sources other than consumption. It is unlikely that ethanol was a factor in the accident.The toxicology results also indicated that both pilots had used sedating antihistamines, and that the flight instructor also had used fentanyl. However, the toxicological results in tissues did not establish whether either pilot was impaired by drug effects at the time of the accident. The flight instructor’s autopsy results and the cardiovascular medications identified on his toxicological testing (specifically losartan, amlodipine, and metoprolol) indicated that he was likely at increased risk of a sudden impairing or incapacitating cardiovascular event such as arrhythmia, heart attack, or stroke. There is no autopsy evidence that such an event occurred, but such an event does not reliably leave autopsy evidence if it occurs just before death, even absent the autopsy limitations that were present in this case. Given that the investigation could not determine which pilot was controlling the gyroplane at the time of the accident, or whether a medical factor contributed to the loss of control, and considering the pilot under instruction had limited skill/experience in the gyroplane, the circumstances of the loss of control could not be determined.