For the 35th Digital Avionics Systems Conference (DASC 2016) dedicated this year to Avionics for UAS/UTM, the Chair’s researchers submitted their work on two topics: the open source autopilot system Paparazzi and the collision avoidance system ACAS Xu. Both abstracts have been accepted by the technical committee and the full papers are currently undergoing a peer review process. This conference is not only an opportunity to spread knowledge in the scientific and industrial communities but also a good occasion to augment the Chair’s visibility at the international level.
Hereafter the titles and abstracts of the papers,
Flexible Open Architecture for UASs Integration into the Airspace : Paparazzi Autopilot System
Air safety authorities are forced to develop regulations for UAS due to incidents disturbing public safety and demands from companies who desire to utilize them. There has been numerous studies, from both the FAA in US and EASA in Europe, but none of them decided on a regulations set for the UAVs to satisfy. Improvement of the reliability of the flight is considered to be one of the main obstacles for integrating UAVs into civil airspace. To achieve a safe flight is not an easy task considering the unknowns of the systems, environment and possible system faults and failures to emerge. To tackle the safety challenges and help the regulation development, NASA is currently carrying out a four years research program (up to 2019) to enable Unmanned aircraft traffic management solutions which are structured yet flexible when needed.
We believe the flexibility required for such solutions calls for open architectures. More specifically, this paper shows how the use of the Paparazzi open source auto-pilot system can ease the integration of low altitude UAS. To ensure safety, this integration needs to be achieved through airspace management and UAS reliability.
The preliminary airspace designs, like the one proposed by Amazon, identify different zones depending on the UAS capabilities, population density and altitude. Plus, different national rules and their progressive refinement pushes to cope with a variety of requirements. Open source and modular architectures are key to adapt these requirements. As a specific example, NASA’s UTM builds, later to be refined by FAA, make modularity essential for UAS software to follow their evolution. From UTM point of view, Paparazzi provide features to ease congestion management. As such, dynamic geofencing allows the use of management methods such as the air parcel model. Moreover, the UASs capacity to send its predicted trajectory to UTM, enables separation not only on the UAVs’ current state, but also based on their trajectories. If separation fails, a TCAS-like collision avoidance module allows avoiding near mid-air collision or worse.
Concerning reliability, current regulations focus on flight constraints but they might be expected to involve regulations on software and hardware components as well. In such case, the increased cost will be inevitable for the demands of certification. This could put too many constraints on UAS manufacturers who desire to access the G airspace. In the Paparazzi software case, parts of the code have been formally proved and stable versions have thousands of flight hours. Such heritage might ease the certification process and allow smaller companies to attend the commercial pie.
On top of its flexibility and reliability, Paparazzi offers a unique set of features, as an open source software, to achieve safe integration of low altitude UAS in the G airspace. To conclude this work, desirable new features (3-D geofencing, collision avoidance and dynamic weather integration) and future work are discussed.
An Introduction to ACAS Xu and the Challenges Ahead
According to a 2013 AUVSI report, delays in integrating Unmanned Aerial Systems (UAS) into the National Airspace System (NAS) could cost more than $10 billions a year for the United States alone. Regulation bodies are under pressure by the UAS industry to accelerate the regulation process, but safety remains their main objective. One condition for the safe introduction of UAS in the NAS is for them to be equipped with a Airborne Collision Avoidance System (ACAS). Though existing Traffic Collision Avoidance System (TCAS) could have been an option, the transformations of air traffic management engaged through NextGen (US) and SESAR (Europe) led to the definition of a new ACAS, namely ACAS X, based on new logics. The ACAS X definition contains in particular two variations : ACAS Xa, for large aircraft, and ACAS Xu, for unmanned aircraft.
As noted in a 2014 RTCA annual report, divide in technological knowledge between those experienced in TCAS and those involved in the development of ACAS X is a concern. To help preventing this divide we believe it is essential to keep the community updated with the latest evolutions of the ACAS X standards. As work on Minimum Operational Performance Standards (MOPS) for ACAS Xu just started, it is of interest to know which parts of the MOPS are already decided, which remain flexible for the industries to make the difference and which are open research problems.
Being a member of the ACAS X family, ACAS Xu lays on the same foundations as the well defined ACAS Xa standard. This work proposes an introduction to the ACAS Xa/Xu common basis, as it is unlikely to change, including the general architecture and Collision Avoidance (CA) logics. It is followed by a presentation of concepts specific to ACAS Xu such as the tailored threat logic, horizontal CA logic, CA coordination and automatic responses. For the flexible part, we believe it mainly concerns the surveillance sources. Instead of a precise standard, the regulation is likely to ask for requirements on the sensors capabilities. A state of the art of recent works allows proposing minimum sensor performances and focusing on an essential set of sensors. This work is concluded by presenting future challenges that need to be addressed to build a safe ACAS Xu baseline and to extend it to smaller and lower altitude UAS.