This work presents a navigation architecture for unmanned aerial vehicles designed to ensure reliable performance in GNSS-denied environments. The proposed system integrates two complementary modules to achieve drift-free navigation under jamming and spoofing. The first module, the AD-AHRS, fuses inertial, magnetometer, and air data measurements to estimate attitude and predict position and velocity states. It also includes integrity monitoring to detect GNSS degradation and accepts corrections from the visual navigation module, which comprises four submodules: visual odometry, template matching, terrain reference navigation, and map matching. Visual odometry estimates velocity by tracking feature displacements across frames, while template matching ence navigation correlates digital elevation models with radar altimeter profiles to mitigate drift at low altitude, whereas at higher altitudes, map matching compares onboard imagery with satellite to GNSS outages and cumulative drift. The paper describes the architecture, presents validation results from datasets, and reports flight tests conducted during Jammertest 2025 under intentional jamming and spoofing.