A system and method for aligning an inertial reference system, which is coupled to a moveable body, is provided. The method includes obtaining unaided navigation state information from an unaided source, and obtaining aiding state information from an aiding source. The unaided navigation state information is generated by the unaided source using navigation information provided by an inertial reference, and the aiding state information is generated by the aiding source using navigation information provided by at least one external reference.The method also includes determining an unaided navigation solution using the unaided navigation state information, and determining an aided navigation solution using a combination of the unaided and aiding state information. As a default, the method provides the unaided navigation solution for navigating the movable body. When the aided navigation solution provides a better solution for navigating the movable body, the unaided navigation solution is replaced with the aided navigation solution.