What happened
During flight, the ZK-DAG, an amateur-built aircraft, experienced a significant structural failure of its tail surfaces. The failure was triggered by aeroelastic flutter that began at the elevator trim tab. This instability led to the disintegration of the tail assembly while the aircraft was still airborne.
The investigation
Investigators examined the wreckage and the mechanical configuration of the aircraft to determine how the flutter was initiated. While the exact reason the aircraft reached a speed high enough to trigger the flutter remains undetermined, the investigation focused on the physical state of the control surfaces. The inquiry established that the aircraft's specific configuration made it uniquely vulnerable to such aerodynamic instability.
Findings
Technical analysis revealed that two specific factors made the ZK-DAG susceptible to flutter at airspeeds lower than those typically experienced by other aircraft of the same model. First, there were identified defects within the trim control system. Second, a modification previously performed on the rudder altered the aircraft's aerodynamic characteristics. These combined factors meant that the aircraft's trim and rudder configuration allowed flutter to occur at a reduced airspeed.
Safety action
As a result of the findings, several safety recommendations were issued to prevent similar occurrences in the amateur-built community and general aviation sector. The Amateur Aircraft Constructors' Association received recommendations regarding the implementation of safer construction techniques. Additionally, the investigation prompted recommendations to the Meteorological Office and the Minister of Transport concerning the quality and detail of weather forecasts provided to general aviation pilots.