What happened
The aircraft was involved in four separate incidents characterized by momentary uncommanded rolls to the right occurring during the rotation phase of takeoff. In each of these four occurrences, the pilot successfully performed corrections to stabilize the aircraft and continued the flight without further complications.
The investigation
Following the fourth incident, maintenance personnel conducted an extensive investigation to identify the source of the rolling sensation. Previous attempts by maintenance staff to diagnose and resolve the issue had been unsuccessful.
Upon inspection, investigators discovered that the left main landing gear strut had been overserviced with nitrogen. The excess pressure in the strut caused the left wing to lift suddenly during rotation as the weight of the aircraft was reduced from the landing gear. This mechanical behavior created the sensation of a roll to the right. Following the discovery, the strut was reserviced with the correct levels of oil and nitrogen.
Additionally, investigators noted that an upper wing surface panel support rod had failed due to high-cycle fatigue, but this component was determined not to be a factor in the uncommanded rolls.