This paper presents a new method for vision-aided navigation of airborne platforms. The method is based on online mosaicking using images acquired by an on-board gimballed camera, which scans ground regions in the vicinity of the flight trajectory. The coupling of the scanning and mosaicking processes improves image-based motion estimation when operating in challenging scenarios such as narrow field-of-view cameras observing low-texture scenes. These improved motion estimations are fused with an inertial navigation system. The mosaic used for navigation is constructed in two levels. A small mosaic based on recently captured images is computed in real-time, and a larger mosaic including all the images is computed in a background process. The low-level mosaic is used for immediate motion estimation, while the higher-level mosaic is used for global navigation. The correlation terms between the navigation system and the mosaic construction process are not maintained in the proposed approach. The advantage of this architecture is the low computational load required for navigation aiding. However, the accuracy of the proposed method could be compromised compared to bearing-only Simultaneous Localization and Mapping (SLAM). The new method was examined using statistical simulation runs and experiments based on Google Earth imagery, showing its superior performance compared to traditional methods for two-view navigation aiding.