Modern aircraft navigation relies heavily on Global Navigation Satellite Systems (GNSS) for both en-route and approach operations. However, the inherent vulnerability of civil GNSS signals to interference underscores the necessity of Alternative Position, Navigation, and Timing (APNT) solutions. This work investigates the integration of GNSS, Distance Measuring Equipment (DME), Inertial Reference System (IRS), Visual sensors, and Air Data Reference (ADR) within two navigation filter architectures: a tightly coupled design exploiting raw GNSS observations, and a loosely coupled design based on GNSS-derived position and velocity. A dedicated filter is further developed for estimating DME measurement biases. Performance is evaluated using real flight data with simulated permanent and intermittent GNSS outages. In parallel, a comprehensive DME error model is proposed, combining Gaussian-distributed nominal errors with transient multipath effects. The error model is subsequently integrated into a previously presented Pose-Based Visual Servoing (PBVS) strategy, and the control approach is validated on a real-time simulation platform during en-route, approach, and landing phases. The results demonstrate the feasibility of robust APNT navigation through hybrid architectures, while establishing an analytical foundation for the integration of DME error models into advanced navigation and control frameworks.