Integrity monitoring in GNSS/INS systems by optical augmentation

Reliable aircraft guidance is one of the main contributors to the high level of safety that is achieved today on modern aircraft. Especially during the landing phase, where aircraft are close to other surrounding traffic and ground obstacles, any undetected deviation from the desired flight path may lead to catastrophic consequences. Automatic landing systems today are based on different ground-based guidance techniques, for example the Instrument Landing System (ILS). They perform well but are expensive in terms of installation and maintenance costs and therefore are only available on bigger airports. In contrast smaller General Aviation (GA) aircraft and regional airports often are not equipped with the above named landing systems. Therefore, this paper presents an alternate low cost aircraft autonomous landing system for GA aircraft, which does not require any type of ground-based navigation equipment. The system consists of a classical GNSS/INS system that is augmented by a new optical positioning system for integrity monitoring. The monitor ensures that any deviation caused by either the navigation system or the guidance system will alert the pilot and trigger an automatic go-around maneuver. This paper outlines the developed system architecture and presents the basic monitoring algorithms. The system was designed in compliance with the Required Navigation Performance (RNP) concept introduced and published by ICAO. The system is still under development and was tested during real flight trials onboard a twin-engine Dornier 128 aircraft during various approaches on Braunschweig airport, see figure 1. This paper presents a profound analysis of the achieved system performance during normal operation and discusses the error budgets that result from the positioning system on the one hand and the flight control deviation on the other. Finally, simulated sensor errors were applied to the recorded flight data in order to demonstrate the fault detection capability within the necessary time to alert. The following analysis presents the performance that can already be achieved by the system today and identify potential gaps with respect to the required system performance.