Mid-air Collision Research Articles

Simulator Training Improves the Estimation of Collision Parameters and the Performance of Student Pilots

Mid-air collisions are among the top ten leading causes of fatal General Aviation accidents. The separation between two aircrafts is a process which depends on multiple dynamic interactions between pilots. This study presents the design and experimental evaluation of a feedback-based training program for ab initio student pilots to anticipate collision parameters and to select appropriate avoidance manoeuvers. The new training programme was evaluated with sixteen student pilots in the flight simulator. The results show that the student pilots significantly improved the accuracy of their estimation of time to collision and their performance in selecting the collision avoidance manoeuvers.

Optimizing a Collision-Avoidance System for Closely Spaced Parallel Operations

The traffic alert and collision-avoidance system has been mandated worldwide to protect against aircraft midair collisions. One drawback of the current traffic alert and collision-avoidance system design is limited support for closely spaced parallel runway operations. The traffic alert and collision-avoidance system alerts, too frequently, leading pilots to often inhibit resolution advisories during approach. Research is underway on the Airborne Collision Avoidance System X, which is a next-generation collision-avoidance system that will support new surveillance systems and air traffic control procedures. The Airborne Collision Avoidance System X has been shown to outperform the traffic alert and collision-avoidance system for en route encounter scenarios. However, the design parameters that are tuned for the en route environment are not appropriate for closely spaced parallel landing operations. One concept to allow for closely spaced parallel landing operations is a procedure-specific mode of the logic that reduces the nuisance alert rate while still providing collision protection. This paper describes the application of surrogate modeling for the purpose of tuning Airborne Collision Avoidance System X for parallel landing operations. The performance of the tuned system is assessed using a data-driven blunder model and an operational performance model. The tuned Airborne Collision Avoidance System X logic is found to equal or outperform the traffic alert and collision-avoidance system for each model in terms of both safety and operational suitability.

공중충돌경보시스템 평가를 위한 통합 무인기 시뮬레이션환경 연구

공중충돌경보시스템 평가를 위한 통합 무인기 시뮬레이션환경 연구

Safety Benefit of Automatic Dependent Surveillance-Broadcast Traffic and Weather Uplink Services

The automatic dependent surveillance-broadcast system serves a dual role for general aviation operators, allowing integration with modern surveillance systems and providing an uplink of traffic, weather, and airspace information to participating aircraft. To obtain automatic dependent surveillance-broadcast uplink services, aircraft must be equipped with a portable or installed “automatic dependent surveillance-broadcast-in” receiver and display. This study used an online survey to assess pilot perception and valuation of automatic dependent surveillance-broadcast-in traffic and weather services, including flight information system-broadcast and traffic information system-broadcast. Of the 1407 pilot respondents to the survey, 56.3% indicated having used automatic dependent surveillance-broadcast-in traffic and weather services while operating an aircraft. Among pilots who reported using automatic dependent surveillance-broadcast-in traffic services regularly, 64.5% reported that it helped them visually acquire traffic and 42.2% felt that the automatic dependent surveillance-broadcast uplink had provided information that helped prevent a midair collision. A strong link was observed between pilot satisfaction with automatic dependent surveillance-broadcast-in traffic information and concurrent equipage with “automatic dependent surveillance-broadcast out.” Pilots also reported using automatic dependent surveillance-broadcast-in weather and airspace services to improve inflight decision making, such as evaluating options for rerouting, changing altitude, or diverting to alternate airports.

Structuring the safety case for unmanned aircraft system operations in non-segregated airspace

Routine access to non-segregated airspace is a key enabler for the civilian Unmanned Aircraft System (UAS) industry. Approvals for UAS operations in this airspace are contingent on the provision of a safety case, which details how the risk of a Mid-Air Collision (MAC) accident will be managed to an acceptable level. There is no accepted framework for structuring operational safety cases for UAS and this gives rise to a number of challenges to the application of the regulation by “safety target” approach. Further, a wide range of controls has been proposed for mitigating the risk, however the effectiveness of the controls is not known. A reconciliation and extension of existing causal models describing the MAC accident sequence is provided in this paper. A barrier bow tie model is developed as a means for structuring the safety case for generic UAS operations in non-segregated airspace. The model is applied to the classification of over 50 commonly used risk controls and the relationship between the control and the manner in which the reduction in MAC risk is achieved is determined. A case-study application is also presented validating the utility of the tool in the development and communication of safety cases for UAS operations in civilian airspace.

The concept of risk situation awareness provision: Towards a new approach for assessing the DSA about the threats and vulnerabilities of complex socio-technical systems

Situation Awareness (SA) is a widely cited and extensively reviewed concept. The context in which SA is examined herein is the complex socio-technical. Hence, the main focus is on Distributed Situation Awareness (DSA) and more precisely on the enhancement and degradation of the awareness regarding the threats and vulnerabilities that the system may possibly encounter. Specifically, by adopting the notion that safety and awareness are inherent and emergent properties of complex socio-technical systems, this paper introduces the novel concept of “risk SA provision”. It is also discussed that the risk SA provision capability is dynamic by nature. Lastly, the Überlingen mid-air collision accident is used to demonstrate that hazard analysis techniques can be employed to create a more detailed image of what constitutes the ‘ideal’ socio-technical system in terms of risk SA provision capabilities. Resting on safety science and control theory, this work suggests a list of system elements and characteristics, which enhance information flow, retrieval, and dissemination and contribute to maintaining the system in an ‘aware’ and safe state. It is also argued that since those system elements are tangible, it seems possible to found a new DSA assessment approach on the measurement of the risk SA provision capabilities of the system.

Evolution of the US Navy's collision avoidance systems (CAS) to future airborne capability environment (FACE)

The US Navy's collision avoidance systems (CAS) software product consists of five different system capabilities: ground proximity warning system (GPWS), terrain awareness warning system (TAWS), obstacle avoidance system (OAS), mid-air collision avoidance system (MCAS), and auto-recovery CAS (AutoCAS). GPWS provides directive controlled fight into terrain (CFIT) protection against fight into level or descending terrain. TAWS provides directive CFIT protection against level, descending, and rising terrain. OAS provides directive protection and situational awareness, through a display, of man-made obstacles. MCAS provides passive protection and awareness of other airborne aircraft. AutoCAS provides active protection by interacting with the avionics system to take control of the aircraft to automatically avoid impact with terrain, obstacles, and/or aircraft. For each capability, the software product provides advisories or directive aural warnings and visual indications to the aircrew. The goal is to maximize protection and minimize nuisance warnings to ensure aircrew trust the system in a dynamic tactical environment [1]. Balancing protection with nuisance warnings is done by embedding an aircraft-specific performance model into the CAS software product.

TCAS Solution to Reduce Alarm Rate in Cockpit and Increase Air Safety

Over the years, air traffic has continued to increase. The development of modern systems has made it possible to cope with this increase, whilst maintaining the necessary level of safety. The Traffic Alert and Collision Avoidance System (TCAS) has been developped to reduce the risk of mid-air collision and is currently mandated on all large transport aircraft This system is based on interrogations to determine the altitude and relative positions of nearby aircraft. Despite technical advances in ATC systems, there are cases when the separation provision fails due to a human or technical error. Any separation provision failures may result in an increased risk of a midair collision. These systems would generate a high rate of unnecessary alarms especially in dense terminal areas and pilots become stressed and wrong actions can be made. A new design of TCAS is investigated in this paper to compensate for any limitations of ATC performance and decrease the rate of unnecessary alerts. It is based on transmitting altitudes and GPS coordinates between aircraft transponders to determine the accurate positions and directions of movement of nearby aircraft.

Analysis of induced Traffic Alert and Collision Avoidance System collisions in unsegregated airspace using a Colored Petri Net model

For rigorously safe aviation, it is of great significance to conduct an analysis of the current and new operations, providing a global perspective of the scenario dynamics and a better understanding of the potential collision occurrence for risk assessment. The objective of this study is to consider a number of the difficulties that are involved when establishing a validation of the Traffic Alert and Collision Avoidance System (TCAS), which constitutes the last resort for reducing the risk of near mid-air collisions between aircraft in a multithread scenario, and to analyze the TCAS logic using a causal model. In this paper, the causal model that is specified in the Colored Petri Net (CPN) formalism is employed as a key approach to analyze quantitatively the state space of a congested traffic scenario in which the events could transform a conflict into a potential collision. It offers a rigorous tool not only for TCAS validation but also for the analysis of a wide range of properties of the TCAS behavior. This CPN model assumes unrestrained initial positions and TCAS II-equipped aircraft; it is demonstrated to be extremely effective for generating all possible future TCAS failure end-states from the current locations, and the Interactive Collision Avoidance Simulator EuroControl simulator is used to illustrate the collision process of a three-aircraft scenario.

Training Pilots for Collision Avoidance Within a Realistic Operating Context

The traffic alert and collision avoidance system has been implemented to reduce the number of midair collisions. Pilot compliance to traffic alert and collision avoidance system resolution advisories is mandated unless the pilot feels it would conflict with safety. Thus, pilots’ responses hinge on their assessment of the situation during the time period leading up to and spanning a traffic alert and collision avoidance system resolution advisory, including assessment of cues that conflict with traffic alert and collision avoidance system guidance. However, current training programs generally do not incorporate a realistic operating context and represent traffic alert and collision avoidance system advisories as isolated events. Furthermore, in the presence of conflicting traffic alert and collision avoidance system guidance and traffic information, pilots have reported confusion about what traffic alert and collision avoidance system advised, as well as disagreement with and noncompliance to resolution advisories. This paper discusses a traffic alert and collision avoidance system training program within a realistic operating context; in this case, the training used an integrated flight-deck/air-traffic-control simulator to create contexts where pilots receive conflicting information from the traffic alert and collision avoidance system and air traffic control. This training significantly impacted pilot responses to resolution advisories, including an increase in compliance when presented conflicting information.

A Socio-technical Model for Analyzing Safety Risk of Unmanned Aircraft Systems (UAS): An Application to Precision Agriculture

There are a number of concerns about the introduction of Unmanned Aircraft Systems (UAS) into the National Airspace System (NAS) of which safety risk is of paramount importance. For UAS that typically fly low and slow, the possibility of a mid-air collision with a nearby general aviation aircraft needs to be studied by identifying possible hazards and assessing mitigations. The Aviation System Risk Model (ASRM) is a first-generation socio-technical model that uses a Bayesian Belief Network (BBN) methodology to integrate possible hazards to assess a non-linear safety risk metric. The ASRM may be used to evaluate underlying causal factors linked to the vehicle and/or to the systems and procedures that led to the unsafe state and the interactions among these factors that contributed to the safety risk. The ASRM can also assess the projected impact of mitigations. The ASRM facilitates robust inductive reasoning on the hypothesized accident scenarios, ideal for addressing emergent NAS operations where there may be obvious data and experience limitations. Recently, the ASRM has been updated with the use of the Hazard Classification and Analysis System (HCAS) that provides analytic structure for categorizing hazards related to the UAS, Airmen, Operations and the Environment. In this paper, the ASRM, together with the HCAS, is demonstrated with a precision agriculture application of a notional scenario that involves an UAS being used for crop scouting. It is conjectured that the UAS interacts with a neighboring farm where a conventional piloted cropduster is being used for pesticide spraying. The UAS being used is a rotorcraft-type where there is a failure of the separation assurance function since the UAS leaves its Area of Operation (AO) due to a Ground Control Station (GCS) transmission disruption (from faulty maintenance) and by the waypoints being incorrectly programmed. The ASRM is used to analyze such a scenario leading to a collision volume being entered by both the UAS and the piloted cropduster that possibly leads to a mid-air collision. The efficacy of a geofence or a “virtual barrier” mitigation for the UAS is also analyzed. The ASRM safety risk results for this notional scenario are presented and interpreted.

Functional resonance analysis method and its application on Zagreb mid-air collision

Functional resonance analysis method and its application on Zagreb mid-air collision

Safety Case as a Necessary Aspect of the Aviation Implementation of the Gnss / Safety Case Jako Niezbędny Aspekt Lotniczej Implementacji Systemu Gnss

Abstract The article describes analysis of the risk for the implementation of precise approach procedures (Localizer Performance and Vertical Guidance - LPV) with GNSS sensor at airports in Warsaw and Katowice. There were used some techniques of the identification of threats (including controlled flight into terrain, landing accident, mid-air collision, missed approach, safe landing) and evaluations methods based on: Event Tree Analysis, probability of the risk, safety risk evaluation matrix and Functional Hazard Assesment. Also safety goals were determined. Research led to determine probabilities of appearing of threats, as well as allow compare them with regard to the ILS. As a result of conducting the Preliminary System Safety Assessment (PSSA), there were defined requirements essential to reach the required level of the safety. Research led to determine probabilities of appearing of threats and safety goals, as well as compare them with regard to the ILS requirements

Stochastic Independence and Causal Connection

Assumptions of stochastic independence are crucial to statistical models in science. Under what circumstances is it reasonable to suppose that two events are independent? When they are not causally or logically connected, so the standard story goes. But scientific models frequently treat causally dependent events as stochastically independent, raising the question whether there are kinds of causal connection that do not undermine stochastic independence. This paper provides one piece of an answer to this question, treating the simple case of two tossed coins with and without a midair collision.

Conflict Management: Apollonius in airspace design

Conflict detection is the process by which potential collisions between aircraft are identified. Developing efficient detection methods is an engineering priority since the prevention of a mid-air collision is a major safety constraint for all airspace design. Proximity between two aircraft each flying with instantaneous uniform straight motion is re-examined. The Apollonius theorem for constructing a circle shows that for a constant speed ratio the locus of all collision points is a circle in the 2D conflict plane (generalised to a sphere in 3D space). This circle provides an effective method and reference for determining the set of all 3D non-allowed steering directions (NASD), which, if followed by ownaircraft, would result in either a collision or proximity of operational concern. The NASD paradigm permits the identification of a protection zone encapsulating the region of potential collision. The method has been applied in the design of static airspace structures and accident analysis as well as providing an explicit solution for the determination of a surface of singularities that are characteristic of force-field guidance laws. The NASD paradigm provides deeper insight into the conflict detection process and represents an increase in the utility, diversity and assessment of design options for future systems.

Can We Automate Compliance to Collision Avoidance Resolution Advisories?

The Traffic alert and Collision Avoidance System (TCAS) was designed to prevent mid-air collisions by portraying a time-critical “resolution advisory” (RA) to the pilot. Complying with a TCAS RA is generally considered the safest course of action and takes priority over all other forms of air traffic management; however, pilot compliance with TCAS RAs is surprisingly low. One proposed solution is an ‘Auto-RA’ function which couples the autoflight system to TCAS such that, when the autopilot is engaged, it automatically executes any corrective RAs. This paper describes a study in an integrated flight deck / air traffic control simulator examining how pilots interact with TCAS with and without an ‘Auto-RA’ function. A prior study found that pilots allowed the autoflight system to fly the RA maneuver in 83% of the runs, but the situations where the pilots disconnected the Auto-RA function generally involved scenarios where pilots received confusing guidance from the RA, and conflicting instructions from air traffic control. Further, once clear of the conflict, pilots appeared to have trouble remembering which autoflight modes they had had engaged before the RA, and air traffic instructions requiring particular speed or altitude targets that were effectively erased by the Auto-RA function. Thus, this study particularly focused on particularly problematic traffic encounters, and on situations where the Auto-RA might disrupt pilots from meeting a specified air traffic restriction.

Saltation of Non-Spherical Sand Particles

Saltation is an important geological process and the primary source of atmospheric mineral dust aerosols. Unfortunately, no studies to date have been able to precisely reproduce the saltation process because of the simplified theoretical models used. For example, sand particles in most of the existing wind sand movement models are considered to be spherical, the effects of the sand shape on the structure of the wind sand flow are rarely studied, and the effect of mid-air collision is usually neglected. In fact, sand grains are rarely round in natural environments. In this paper, we first analyzed the drag coefficients, drag forces, and starting friction wind speeds of sand grains with different shapes in the saltation process, then established a sand saltation model that considers the coupling effect between wind and the sand grains, the effect of the mid-air collision of sand grains, and the effect of the sand grain shape. Based on this model, the saltation process and sand transport rate of non-spherical sand particles were simulated. The results show that the sand shape has a significant impact on the saltation process; for the same wind speed, the sand transport rates varied for different shapes of sand grains by as much as several-fold. Therefore, sand shape is one of the important factors affecting wind-sand movement.

Error model estimation for airborne beacon‐based surveillance

A next-generation aircraft collision avoidance system under development is designed to reduce unnecessary alerts while reducing the risk of mid-air collision. Current and future collision avoidance systems rely upon range, bearing and altitude information from airborne, beacon-based surveillance. Realistic models of surveillance error characteristics are needed in order to develop and certify the safety and performance of these systems. Prior models of bearing measurements assumed uncorrelated Gaussian noise. This study explains how hidden Markov models can be used to capture the time-correlated error characteristics exhibited by recorded surveillance data. Simulations show the impact of this higher-fidelity model on predicted collision avoidance performance.

A causal model to explore the ACAS induced collisions

Current Air Traffic Management research programs (i.e. Single European Sky ATM (air traffic management) Research (SESAR), next generation air transportation system (NextGen)), try to overcome airside capacity shortages while improving cost-efficient operations and safety. An increment in the airspace traffic density can lead to congested traffic scenarios for which it becomes necessary to develop new safety procedures that address multithread threats. This paper considers some of the difficulties in establishing validation of the airborne collision avoidance system (ACAS), which constitutes the last-resort for reducing the risk of near mid-air collision between aircraft in a multithread scenario. A causal model that is specified in Colored Petri Net (CPN) formalism is presented as a key approach to analyze the state space of a congested traffic scenario in which the events that could transform a conflict into a collision are identified, providing a challenging tool not only for validation but also for the implementation of a new ACAS logic. The InCAS EuroControl simulator has been used to illustrate the importance of cause–effect analysis for the relationships between various encounters that arise in a multithread scenario, in which TCAS II v. 7.1 fails to avoid a collision when two Resolution Advisories are issued without consideration of the downstream effects.

Safety Comparison of Centralized and Distributed Aircraft Separation Assurance Concepts

This paper presents several models to compare centralized and distributed automated separation assurance concepts in aviation. In a centralized system, safety-related functions are implemented by common equipment on the ground. In a distributed system, safety-related functions are implemented by equipment on each aircraft. Failures of the safety-related functions can increase the risk of near mid-air collisions. Intuitively, failures on the ground are worse than failures in the air because the ground failures simultaneously affect multiple aircraft. This paper evaluates the degree to which this belief is true. Using region-wide models to account for dependencies between aircraft pairs, we derive the region-wide expectation and variance of the number of separation losses for both centralized and distributed concepts. This derivation is done first for a basic scenario involving a single component and function. We show that the variance of the number of separation losses is always higher for the centralized system, holding the expectations equal. However, numerical examples show that the difference is negligible when the events of interest are rare. Results are extended to a hybrid centralized-distributed scenario involving multiple components and functions on the ground and in the air. In this case, the variance of the centralized system may actually be less than that of the distributed system. The overall implication is that the common-cause failure of the ground function does not seriously weaken the overall case for using a centralized concept versus a distributed concept.