The airborne sensors with high data rate demand the onboard high-speed storage system due to the limited bandwidth of the downlinks. The NAND Flash and its products are the most common storage medium, and the conventional FAT file system is widely used in the storage systems. However, there has been a problem in recording the live high-speed data stably with this file system. The management time of the FAT file system is relatively long due to the internal overhead which includes the retrieving and updating of the FAT and FDT. The aim of this study is to investigate the technology for the real-time file system. A technology called FPFPA (FAT post- and FDT post- allocation) method is presented to solve this problem. To evaluate the performance of the proposed method, the management time of the file system using our proposed method is tested on the high-speed storage system of an airborne radar. The result indicates that the proposed method achieves our goal successfully in that the management time of the file system is significantly reduced and sufficiently small.