Incidents
An aircraft was involved in four separate instances of momentary uncommanded rolls to the right during rotation. In each case, the pilot was able to quickly correct the situation and continue the flight without further problems.
Investigation
Numerous attempts by maintenance personnel to identify and resolve the issue were unsuccessful. After the fourth incident, the left main landing gear strut was found to have been overserviced with nitrogen. The additional pressure to the strut would suddenly lift the left wing during rotation when the weight of the aircraft on the landing gear is reduced, thus giving the pilots a rolling sensation to the right.
Resolution
The strut was reserviced with oil and nitrogen, and the aircraft was returned to service with no more occurrences.
Additional Findings
An upper wing surface panel support rod was found broken due to high-cycle fatigue, but it was not considered a factor in these instances.