Terrain-Referenced Precision Approach Guidance: Proof-of-Concept Flight Test Results

Aircraft precision approach guidance systems require accurate positioning relative to the runway with a high level of integrity. Most precision approach guidance systems in use today require ground-based electronic navigation components with at least one installation at each airport, and in many cases multiple installations to service approaches to all qualifying runway ends. A terrain-referenced approach guidance system is envisioned to provide precision guidance to an aircraft without the use of ground-based electronic navigation components installed at the airport. An Airborne Laser Scanner (ALS), when integrated with an Inertial Measurement Unit (IMU) and a Digital Elevation Model (DEM) with approximately a 1 m horizontal resolution and elevation accuracy on the order of 30 cm RMS, can provide navigation and guidance information in support of aircraft precision approach and landing operations. The proof-of-concept terrain-referenced navigation system provides horizontal and vertical position estimates with accuracies on the order of one meter RMS and capitalizes on the position and integrity benefits provided by the Global Positioning System (GPS) Wide Area Augmentation System (WAAS) to reduce the terrain navigator’s initial position search space size and to reduce the required size of the high accuracy/high resolution database. This paper describes the proof-of-concept aircraft approach system and presents results from flight tests where the approach system is used to provide realtime guidance cues to the pilot.