A system and to a method of analyzing and monitoring interfering movements of an inertial unit of an aircraft during a stage of statically aligning the inertial unit. During the static alignment stage, measurements of the velocity of the aircraft relative to the ground are acquired, and states of a mirror process having a model that is close to the model of the process of aligning the inertial unit are estimated. The states of the mirror process are estimated from observations constituted by the measurements of velocity relative to the ground. Finally, the estimates of the states are compared with respective validation thresholds in order to validate or not validate said alignment of the inertial unit.