Probabilistic Safety Assessment for UAS Separation Assurance and Collision Avoidance Systems

Abstract

The airworthiness certification of aerospace cyber-physical systems traditionally relies on the probabilistic safety assessment as a standard engineering methodology to quantify the potential risks associated with faults in system components. This paper presents and discusses the probabilistic safety assessment of detect and avoid (DAA) systems relying on multiple cooperative and non-cooperative tracking technologies to identify the risk of collision of unmanned aircraft systems (UAS) with other flight vehicles. In particular, fault tree analysis (FTA) is utilized to measure the overall system unavailability for each basic component failure. Considering the inter-dependencies of navigation and surveillance systems, the common cause failure (CCF)-beta model is applied to calculate the system risk associated with common failures. Additionally, an importance analysis is conducted to quantify the safety measures and identify the most significant component failures. Results indicate that the failure in traffic detection by cooperative surveillance systems contribute more to the overall DAA system functionality and that the probability of failure for ownship locatability in cooperative surveillance is greater than its traffic detection function. Although all the sensors individually yield 99.9% operational availability, the implementation of adequate multi-sensor DAA system relying on both cooperative and non-cooperative technologies is shown to be necessary to achieve the desired levels of safety in all possible encounters. These results strongly support the adoption of a unified analytical framework for cooperative/non-cooperative UAS DAA and elicits an evolution of the current certification framework to properly account for artificial intelligence and machine-learning based systems.

On Probabilistic Risk of Aircraft Collision along Air Corridors

“…The fundamental problem addressed in this paper of ensuring extremely low collision probabilities has implications for conflict resolution measures [55,56], which apply both to manned and unmanned aircraft if operating in non-segregated airspace [57][58][59], as an alternative to geofencing [60]. Conflict resolution may be automated [61] if reliable trajectory information is available [62], which is not always the case, for example for aircraft collision with birds [63].…”

“…The magnitude of the correction factor in Tables 5 and 6 is an indication of the sensitivity of collision probabilities to the choice of probability distribution. 2 was calculated for a Gaussian probability distribution (59) and is recalculated for a generalized exponential probability distribution (57), using the correction factor (65). 2 for a reduced vertical separation L = 1000 ft (as in Table 3) with correction factor of the generalized error probability distribution relative to the Gaussian (as in Table 5).…”

Initial Reliability Assessment of a Commercial-Off-The-Shelf GPS Sensor for Generic UAVs

“…Studies have considered the use of fault tree analysis for UAS systems and GPS sensors have been one of the casual events [30], [31]. However, in these studies top-level events are hardware, such as ADS-B, that large UAS are generally equipped with, contrary to small UAS being considered in this paper.…”

Dynamic Control Allocation between Onboard and Delayed Remote Control for Unmanned Aircraft System Detect-and-Avoid

“…As UAS applications continue to expand, researches have been carried out on the path prediction, tracking and control as well as collision avoidance algorithm development [27,28,29,30,31,32,33,34]. Detect-and-Avoid concept of operation is illustrated in [35] and several studies [36,37,38,29,39] specifically focus on the safety critical analysis of a standalone DAA with different methodologies as well as design of cognitive pilot-machine interface [40,41]. When implementing a shared architecture with UAS DAA, it is important to consider any inconsistency or latency that exists in the communication channel, since communication is crucial for sending surveillance information to ground control station and receiving pilot command.…”