Traffic Alert And Collision Avoidance System Research Articles

Reliably Creating Collision Avoidance Advisories in Piloted Simulations

We demonstrate a novel method to reliably generate collision avoidance advisories, in piloted simulations, by the widely used traffic alert and collision avoidance system (TCAS). The TCAS advisory issued to a pilot is highly sensitive to the trajectory of an intruder aircraft relative to the ownship flown by the pilot. In realistic piloted simulations, a prescripted intruder trajectory will not reliably result in the relative dynamics that lead to a desired TCAS advisory. Further, the complexity of the TCAS logic requires a novel method for mapping trajectories to the range of possible advisories. We propose to use a rapidly exploring random tree algorithm in large-scale fast-time simulations to establish the mapping between the space of relative trajectories and TCAS advisories. These trajectories are then created in piloted simulations through guidance algorithms. Results demonstrate the ease of use and robustness of this method, and its potential for pilot training and for research and development.

Optimizing the Next Generation Collision Avoidance System for Safe, Suitable, and Acceptable Operational Performance

The Traffic Alert and Collision Avoidance System (TCAS) is mandated worldwide on large commercial aircraft and has been shown to substantially reduce the risk of mid-air collision. However, the logic used to select pilot advisories is difficult to modify and does not easily support new surveillance inputs. The next generation system, called Airborne Collision Avoidance System (ACAS X), currently addresses many of the design limitations of TCAS. ACAS X is optimized with respect to a cost function. The system was initially optimized to increase safety and decrease alerts. Recent work has focused on tuning ACAS X to also meet operational suitability and pilot acceptability performance metrics. An iterative tuning process reduced the operational impact on the air traffic system and improved acceptability of alerts. This paper summarizes a 15-month effort that resulted in substantial improvements. Compared with TCAS, ACAS X reduces collision risk by 59%, lowers the alert rate by 50%, and issues 28% fewer disruptive alerts. ACAS X also resolves encounters with simpler alert sequences and issues less than half as many reversal and altitude crossing advisories.

Introducing Unmanned Aircraft Systems into a High Reliability ATC System

Civil and military unmanned aircraft systems (UAS) operations are currently subject to restrictions that put major limits on their use of airspace. There is considerable debate about how to develop the safe, secure and efficient integration of UAS into non-segregated airspace and aerodromes. This paper examines a necessary safety aspect. Airlines and their passengers would obviously ask, “Is it still safe with all these unmanned aircraft around?” The spotlight must be on Air Traffic Control Systems as High Reliability Organizations (HRO). That status comes from industry characteristics: focus on safety, effective use of technological improvements, learning from feedback from accidents/incidents, and an underpinning safety culture. The safety of ATC Systems has improved dramatically: accidents are now the product of rare and complex ‘messes’ of multiple failures. It is therefore a major challenge to preserve the HRO status by ensuring at least current safety performance. The analysis sketches feasible processes of policy decision-making and safety analyses. Key factors are policies on UAS equipage and airspace usage, implementation of a Traffic Alert and Collision Avoidance System (TCAS)-variant appropriate for UAS, use of an ‘Equivalent Level of Safety’ philosophy, small datalink latencies, proven HRO safety and learning cultures, and stress testing of system resilience by real-time simulations.

Integration of Radar System with GPS-Based Traffic Alert and Collision Avoidance System (TCAS) for Approach Control Separation

The air traffic control system is a vast network of people and necessary navigational equipment that ensures the safe operation of commercial and private aircraft throughout the world. Air traffic controller service is responsible for area, approach and aerodrome control. Aircraft fatal accident data for commercial jet airplanes between 1959 and 2008 show that 36% of the accidents happen in the final approach and landing phase, possibly due to mechanical failure or human error resulting from poor communication between the pilot and air traffic controller. This paper presents an integration of a radar system with a GPS-based Traffic Alert and Collision Avoidance System (TCAS) for approach control separation between all instrument flight rules (IFR) flights and between IFR flights and visual flight rules (VFR) flights operated as controlled flights. The integration is simulated using MATLAB. Results of the simulation show that aircraft separation is easier and safer than relying only on an air traffic controller. We note, however, that the service of air traffic controllers is still required for successful aerodrome control.

Pilot’s Information Use During TCAS Events, and Relationship to Compliance to TCAS Resolution Advisories

The Traffic alert and Collision Avoidance System (TCAS) is intended to serve as a backup, redundant system that alerts and advises the pilot when all other methods of aircraft separation assurance fail. A flight simulator experiment examined pilot responses to TCAS advisories in a full air traffic environment. This paper discusses two analyses of the pilots’ use of information within their environment. The first analysis examined air traffic communications manipulated according to four conditions: traffic call-outs, instructions conflicting with the TCAS advised avoidance maneuver, the ability to over-hear relevant party-line information, and no relevant communications. The second analysis used data from an eye tracker to identify when the pilot examined the traffic situation display provided by TCAS. These patterns of information use are then compared with pilot compliance to the Resolution Advisories provided by TCAS.

TCAS software verification using constraint programming

AbstractSafety-critical software must be thoroughly verified before being exploited in commercial applications. In particular, any TCAS (Traffic Alert and Collision Avoidance System) implementation must be verified against safety properties extracted from the anti-collision theory that regulates the controlled airspace. This verification step is currently realized with manual code reviews and testing. In our work, we explore the capabilities of Constraint Programming for automated software verification and testing. We built a dedicated constraint solving procedure that combines constraint propagation with Linear Programming to solve conditional disjunctive constraint systems over bounded integers extracted from computer programs and safety properties. An experience we made on verifying a publicly available TCAS component implementation against a set of safety-critical properties showed that this approach is viable and efficient.

Research on software testing technique of airborne equipment based on airworthiness

According to the characteristics of the airborne embedded software, the airworthiness-based software testing technique and testing standard are systematically researched. The verification process of DO-178B standard is analyzed. The software integration testing process of airborne TCAS (Traffic Alert and Collision Avoidance System) is designed. The TCAS software testing project is finished in the hardware testing environment with the software testing tools. The improvement of the testing procedure defects are analyzed. Test result and the comparsion results are presented and analyzed. The correctness and the versatility of the testing model and the testing process are approved by the test examples.

Sense & Avoid capability development challenges

Unmanned Aircraft Systems will require a Sense & Avoid function to protect against collisions with other aircraft as well as various other hazards. Architectural alternatives in the distributions of functionality between aircraft and a ground control station make the development of requirements and standards more complex. A broad variety of candidate sensor technologies has the potential to fulfill the surveillance portion of the system. This explores the capabilities and limitations of these technologies, and suggests deploying combinations of technologies to capitalize upon their respective strengths. A discussion of algorithmic requirements draws upon the experience of the Traffic Alert and Collision Avoidance System (TCAS) in the airspace. Differences and challenges in implementing an algorithm for a UAS are discussed. The broad range of UAS aerodynamic characteristics complicate the process of standardizing an algorithm for Sense & Avoid. In order to build a safety case supporting the certification of a UAS, its performance must be thoroughly evaluated. In the case of Sense & Avoid, flight testing cannot be sufficiently thorough, and instead, the simulation of the system for large numbers of aircraft encounters is recommended. This discusses the considerations in performing such simulations, and in modeling various components of the system and of the potential encounter geometries. Unlike TCAS, an encounter model cannot be constructed solely from observed data, as UAS are not yet performing the desired uses. The Sense & Avoid work within the RTCA SC-203 standards committee is described.

Monitoring of TCAS Resolution Advisories in Core European Airspace

Downlink and display of Resolution Advisories (RAs) – which are issued by the airborne Traffic alert and Collision Avoidance System (TCAS) – has been proposed as a means of informing the air traffic controller that an RA has been posted onboard the aircraft. Previous research has pointed to a number of operational benefits of RA downlink display, such as an improved controller situational awareness and a smaller likelihood of contradictory clearances to aircraft involved in an RA event. However, these benefits of RA downlink display only pertain to RAs that, if complied with, cause a deviation from the Air Traffic Control (ATC) clearance. In order to investigate the frequency and type of RAs in core European airspace, EUROCONTROL initiated the PASS monitoring study. Within this study, RA downlink data from six Mode-S radars covering a large part of the core European airspace were collected from September 2007 to March 2008. The results of the monitoring indicate that approximately a fourth of the RAs issued are likely to cause a deviation from the ATC clearance. However, because of the low overall number of RA encounters (i.e. 1 RA encounter per 2160 flight hours), the display of all RAs – including those that do not yield a deviation from the ATC clearance – is not likely to cause problems related to screen clutter or controller desensitization. On the basis of the results of the RA monitoring, some concerns are identified and refinements to the operational concept for RA downlink display are proposed.

Verification of cooperating traffic agents

This paper exploits design patterns employed in coordinating autonomous transport vehicles in order to ease the burden in verifying cooperating hybrid systems. The presented verification methodology is equally applicable for avionics applications (such as the traffic alert and collision avoidance system (TCAS)), train applications (such as the European train control system (ETCS)), or automotive applications (such as platooning). We present a verification rule explicating the essence of employed design patterns, guaranteeing global safety properties of the kind “a collision will never occur”, and whose premises can either be established by off-line analysis of the worst-case behaviour of the involved traffic agents, or by purely local proofs, involving only a single traffic agent. A companion paper will show how such local proof obligations can be discharged automatically.

STCA, TCAS, Airproxes and Collision Risk

The focus here is on the performance of and interaction between the Traffic Alert and Collision Avoidance System (TCAS) and the controller's short-term conflict alert (STCA) system. The data source used is UK Airprox Board Reports of close encounters between aircraft, and the focus is on commercial air transport aircraft using UK controlled airspace with a radar service. Do the systems work well together? Are controllers surprised when they find out that a pilot has received a TCAS resolution advisory? What do TCAS and STCA events say about collision risk? Generally, the systems seem to work together well. On most occasions, controllers are not surprised by TCAS advisories: either they have detected the problem themselves or STCA has alerted them to it. The statistically expected rate of future mid-air collisions is estimated by extrapolation of Airprox closest encounter distances.

Initial Efforts Toward Identifying Aviation Alerting System Dissonance

The possibility that different alerting systems transmit conflicting information is increasingly possible as these systems become pervasive in aerospace. This article describes a methodology that has been recently developed to provide a foundation for understanding, identifying, and resolving dissonance between alerting systems. Provided as an example of the system application is the recently proposed airborne conflict management (ACM) system which must operate in conjunction with existing traffic alert and collision avoidance systems (TCAS). Dissonant operating regions for TCAS and ACM are articulated, and it is shown that in some geometrics potentially undesirable TCAS advisories may occur following action taken in response to ACM alerts.

Inflight path planning replacing pure collision avoidance, using ADS-B

This paper proposes a method of collision avoidance planning using automatic dependent surveillance-broadcast (ADS-B) and dynamic programming (DP). It in essence allows air traffic control (ATC) within the cockpit for remote or uncontrolled airspace and is a step toward Free Flight. This paper reviews the approach to collision avoidance in the aircraft industry and to similar problems in other industries. DP is one solution method used in other industries for the problem of path planning to avoid collisions with fixed obstacles. The solution proposed here for the aircraft case uses DP applied to the moving obstacle case. The problem is first simplified by assuming fixed obstacles for the cost minimisation algorithms. These fixed obstacles are then moved with time and the minimisation process is started again. Although this method works well in most cases, situations can be constructed where this method fails, allowing a collision. A modified approach is proposed, where the movement of obstacles is included more explicitly in the cost minimisation algorithm. This modification allows solutions which are complete and ensures safe maneuvres and should be considered as an aid to the Traffic alert and Collision Avoidance System (TCAS).

High-level modeling and analysis of the traffic alert and collision avoidance system (TCAS)

We demonstrate a high-level approach to modeling, analyzing, and verifying complex safety-critical systems through a case study on the traffic alert and collision avoidance system (TCAS); an avionics system that detects and resolves aircraft collision threats. Due to the complexity of the TCAS software and the hybrid nature of the closed-loop system, the traditional testing technique of exhaustive simulation does not constitute a viable verification approach. Moreover, the detailed specification of the system software employed to date as a means toward analysis and verification neither helps in intuitively understanding the behavior of the system nor enables the analysis of the closed-loop system behavior. We advocate defining high-level hybrid system models that capture the behavior not only of the software but also of the airplanes, sensors, pilots, etc. In particular, we show how the core components of TCAS can be captured by relatively simple hybrid I/O automata, which are amenable to format analysis. We then outline a methodology for establishing conditions under which TCAS guarantees sufficient separation in altitude for aircraft involved in collision threats. The contributions of the paper are the high-level models of the closed-loop TCAS system and the demonstration of the usefulness of high-level modeling, analysis, and verification techniques.

Performance Analysis of a Horizontal Miss Distance Filter for TCAS II

This paper describes the performance of a filter for reducing unnecessary alerts from the Traffic Alert and Collision Avoidance System (TCAS). The filter uses range and bearing measurements to estimate miss distance for potential threat aircraft. When the estimated miss distance is high, TCAS resolution advisories are suppressed. The filter has been prototyped and extensively tested in MITRE’s TCAS simulation test bed. When implemented, the filter is expected to reduce TCAS resolution advisories by about 25% in US airspace and by about 40% in European airspace, while having a negligible effect on system safety. The filter will be included in the next fielded version of TCAS.

Methodology for alerting-system performance evaluation

A probabilistic-analysis methodology is described that provides quantitative measures of alerting-system performance, including the probabilities of a false alarm and missed detection. As part of the approach, the alerting decision is recast as a signal-detection problem, and system operating-characteristic curves are introduced to describe the tradeoffs between alerting-threshold placement and system performance. The methodology fills the need for a means to determine appropriate alerting thresholds and to quantify the potential benefits that are possible through changes in the design of the system. Because the methodology is developed in a generalized manner, it can be used in a variety of vehicle, transportation-system, and process-control applications. The methodology is demonstrated through an example application to the Traffic Alert and Collision Avoidance System (TCAS). Recent changes in TCAS alerting thresholds are shown to reduce the probability of a false alarm in situations known to produce frequent nuisance alerts in actual operations. Nomenclature A, N, T = probabilistic-state trajectories E = event of encountering a hazard fx (x) = probability density function for the random variable x h = estimated relative altitude h = estimated relative-altitude rate / = incident event ^maif - probability of alerting-system malfunction P(x) = probability of event ;c PT(X) = probability of event x evaluated along trajectory T r = estimated relative range r = estimated relative-range rate

Head-Up Auditory Display Research at NASA Ames Research Center

The use of spatialized (“3-D”) audio techniques for head-up auditory displays for commercial aircraft has been investigated at NASA Ames Research Center since 1989. Results from two completed studies are presented, where a 3-D audio Traffic alert and Collision Avoidance System (TCAS) was designed and evaluated in a full mission simulation context. An experiment-in-progress evaluates the application of 3-D audio for gate identification and collision avoidance with other aircraft, as part of NASA's Terminal Area Productivity-Low Visibility Landing and Surface Operations (Lo Vlaso) program.

A Probabilistic Methodology for the Evaluation of Alerting System Performance

A probabilistic methodology for evaluating hazard alerting systems is described that can be used in vehicle, transportation system, and process control applications. A means of showing the tradeoff between false alarms and missed detections is presented using signal detection theory concepts. The methodology accounts for uncertainties in measurement sources, alerting thresholds and displays, the human operator, and the situation dynamics. An example demonstration of the methodology is provided using the Traffic Alert and Collision Avoidance System (TCAS), an alerting system designed to prevent mid-air collisions between aircraft

Contracts

Turkish Airlines (THY) has chosen Honeywell to supply Traffic Alert and Collision Avoidance Systems (TCAS) for its Airbus A310s and A340s and Global Positioning/Air Data Inertial Reference Systems (GP/ADIRS) for its A340s.

TCAS in the 1990s

The Traffic Alert and Collision Avoidance System (TCAS) is the culmination of over 30 years of work by the aviation community to develop an airborne collision avoidance system that will complement the FAA's ground-based air traffic control (ATC) system. Use of the existing ATC radar transponders provides the basis for TCAS. A collision avoidance system based on ATC transponders has the advantage that it can provide immediate, high-quality protection against the large population of aircraft already transponder-equipped. The airborne TCAS uses transponder information to track nearby aircraft. This tracking data is used to develop and display in the cockpit advisory information that advises the pilot in maneuvering to avoid threat aircraft. This paper describes the design, operation, and application of the three versions of TCAS (TCAS I, II, and III), and continuing development and implementation of TCAS during the 1990s. TCAS II is stressed since it is already in use by U.S. airlines.