However , even though it was determined Deciding that the wing was destroyed Destroying by `` cycles of reverse bending Motion '' or `` flutter '' , the investigation Criminal_investigation failed to determine Deciding how the flutter Motion was caused Causation , and the investigation Criminal_investigation stalled Change_event_time .

In the six months following the accident Catastrophe further progress Cause_to_make_progress towards identifying Check the cause Causation of the flutter Motion was unsuccessful and the case remained unsolved .

However , even though it was determined Deciding that the wing was destroyed Destroying by `` cycles of reverse bending Motion '' or `` flutter '' , the investigation Criminal_investigation failed to determine Deciding how the flutter Motion was caused Causation , and the investigation Criminal_investigation stalled Change_event_time .

They believed Know that the empennage had failed due Causation to flutter Motion .

Weather reports Reporting from surrounding Surrounding communities as well as the existence Presence of the dust storm Catastrophe in Bozeman Pass led Causation investigators to believe that the aircraft likely encountered severe to extreme turbulence which may have initiated Process_start the flutter Motion .

The Department ordered Request that the rudders of all Super Electras be modified Change so as to eliminate Removing the possibility that flutter Motion would cause Causation an in-flight break-up Destroying .