Unaugmented GPS-Based Flight Inspection System

A unaugmented Global Positioning System (GPS)-based flight inspection system (FIS) that performs airborne inspection of the instrument landing system (ILS) is introduced. This novel system relies on a TV positioning system (TVPS) that measures the horizontal position over the runway threshold and a radar altimeter (RA) to determine a reference point that is able to remove the GPS biases. Because of the near-real-time nature of flight inspection, it is possible to reconstruct an accurate approach trajectory even though the reference point occurs after the completion of the trajectory. The precise relative positioning (PRP) algorithm is applied to achieve the desired results. It includes a first-order fit to the ionospheric error, based on code and carrier measurements, that enables a significant reduction in this error source. This system has an autonomous integrity feature, called FIS-RAIM (receiver autonomous integrity monitoring), that is equipped in this system to protect against GPS satellite failures that may cause significant positioning errors. The FIS-RAIM is specifically designed for a flight inspection problem, and much of its detail is also described. Experimental flight tests strongly suggest that the system architecture and algorithm could meet FIS accuracy requirements for CAT III ILS with better performance than current flight inspection systems in terms of cost and efficiency. The system is not dependent on any GPS augmentation system; therefore the unaugmented GPS-based FIS provides low cost and high efficiency with worldwide availability.