Beech 95 N2024C accident near Yuma, Arizona

Probable cause

Aeroelastic flutter of the rudder control surface during the takeoff initial climb for reasons that could not be determined based on the available evidence, which resulted in the fracture of the rudder trim control rod end in flight.

NTSB analysis

Shortly after departing on the instructional flight, the pilot receiving instruction noted the rudder pedals moving back and forth without his input. The flight instructor assumed control of the airplane, also felt the rudder pedals moving, and chose to return to the airport. The oscillation of the rudder pedals intensified, the airplane began to shake violently, and the windscreen separated from the airplane. The pilots declared an emergency and subsequently landed uneventfully at the departure airport.

Postaccident examination of the airplane revealed that the rudder trim control rod end was fracture separated near the trim tab attachment point. Metallurgical examination revealed fatigue cracking parallel to the clevis attachment bolt. The overall fracture was consistent with fatigue crack growth from bending loads on the fitting where the bending moment’s axis was parallel to the clevis attachment bolt axis. It is likely that buckling of the control rod end produced the fatigue crack initiation and propagation. The fracture surface appeared free of any substantial long-term oxidation from a preexisting crack, suggesting that the fracture likely occurred due to repeated, high-compressive loads associated with the reported rudder trim flutter condition, and was secondary to the flutter condition, not the cause.

Flutter is governed by aircraft speed, structural stiffness, and mass distribution. An increase in airspeed, a reduction in structural stiffness, or a change in mass distribution can increase the susceptibility to flutter. Review of maintenance records revealed that maintenance had been performed on the rudder trim tab hardware about one month before the accident flight. While it is likely that the flutter event developed first and resulted in the fracture of the rudder trim control rod end, the initiating event of the rudder flutter could not be determined based on the available evidence.

Text from the NTSB. Open the NTSB docket for WPR24LA038 for the full record.