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The International Civil Aviation Organization (ICAO) specifies that in the design phase of instrument flight procedures, an additional clearance may be added to an obstacle when flights are over mountainous terrain. This clearance increase can be up to 100 per cent of the minimum obstacle clearance (MOC). Airspace and instrument flight procedure designers usually face the problem of determining what value should be applied, since setting the maximum value of 100% often implies operational penalties, but there are no standardized criteria to determine lower values. The ICAO PANS-OPS indicates that the additional clearance over obstacles in mountainous areas is caused by two effects, both related to orography and wind speed. The first effect is due to the altimeter indication error. The second one is related to the loss of altitude when an aircraft is exposed to turbulence produced by mountain waves. This paper presents a methodology for determining the additional clearance to be applied over obstacles when, in the flight procedure design phase, the overflight of mountainous terrain is expected. Through this methodology, results have been achieved for the proposal of an appropriate additional clearance. The development of graphs and tables allows us to identify which additional value should be considered in each case. [ABSTRACT FROM AUTHOR]

A major challenge for the Air Traffic Management system is the need to boost airspace capacity, which is near saturation in some situations. Separation minima are one of the factors related to airspace capacity, and the SESAR program promotes research into advanced separation modes. Ad Hoc separation, a novel separation mode, involves applying different pairwise separation minima in the same volume of airspace depending on a set of factors, such as encounter geometry, aircraft models, and flight level, among others. This research examines the impact of implementing this concept in different en-route scenarios. The goal is to determine whether applying this concept proves advantageous or, conversely, results in an increase in the complexity of the system without significant benefits in the key performance areas of capacity, environment, and cost-efficiency. Fast Time Simulations are conducted in RAMS software, with the concept being implemented in the LECMZMU, LECMTLU, and LECMDGU sectors of the Madrid ACC. The results reveal favorable capacity outcomes with increases of around 2% and the LECMZMU sector exhibits the most significant environmental and cost-efficiency benefits. Furthermore, implementing the Ad Hoc concept in a larger scenario could yield even greater environmental and cost-efficiency benefits. [ABSTRACT FROM AUTHOR]

The expected growth of air traffic in the coming decades demands an increase in airspace capacity, which is already close to saturation in many scenarios. One of the limiting factors of this capacity is the separation minima. At present, the separation standards that apply in a given volume of airspace are fixed, and their values were determined decades ago. Therefore, in order to increase airspace capacity, this is an area in which improvement is sought, namely through the implementation of new operational concepts, which include the redefinition of separation minima and the way they are applied. A key issue in this redefinition of separation minima is the question of the possibility of reducing the current standards. However, a reduction in the separation to a fixed value may not be a valid solution, as not all aircraft and ways of operation are the same. In this paper, the authors propose a new operational concept, the Ad Hoc or Variable separation minima. Ad Hoc separation refers to the application of different separation minima values in the same volume of airspace, depending on a set of factors, e.g., aircraft model and encounter geometry, among others. In this research, the factors that define these Ad Hoc separation minima and their relationships are discussed. A model for their determination is presented. Simulations are performed to analyze the operational feasibility of the Ad Hoc separation minima. The results show that the application of this concept is operationally feasible. [ABSTRACT FROM AUTHOR]

The current Air Traffic Management (ATM) functional approach is changing: ‘time’ is now integrated as an additional fourth dimension on trajectories. This notion will impose on aircraft the compliance of accurately arrival times over designated checkpoints, called Time Windows (TWs). In this context, we review the operational concept of 4D-trajectories, by initially developing an analysis of basic requirements for their implementation in the Communications, Navigation and Surveillance (CNS) systems and then by investigating their management in the future ATM context. We focus on defining the relationships between 4D-trajectories and other concepts and systems of the future ATM framework, and the needs that it will require for its application, detailing the main tools, programs and ATM/CNS systems that must be deployed. We appraise how 4D-trajectories must be managed and planned (negotiation, synchronization, modification and verification processes). Then, based on the degradation of a 4D-trajectory, we define and introduce the necessary corrective measures by evaluating the degradation tolerances and conditions.

The forthcoming integration of Remotely Piloted Aircraft System (RPAS) is one of the cmost omplex challenges for aviation. Europe draws to allow operating RPAS and conventional aircraft in non-segregated airspace by 2025, but this demanding perspective entails a thorough analysis of the different aspects involved. The RPAS integration in non-segregated airspace cannot imply an increase in the safety levels. This paper assesses how the RPAS integration affects safety levels. The goal is to regulate the number of RPAS that can jointly operate with conventional aircraft regarding conflict risk. This approach benchmarks a Calculated Level of Safety (CLS) with a Target Level of Safety (TLS). Monte Carlo (MC) simulations quantify the TLS based on schedules of conventional aircraft. Then, different combinations of conventional aircraft and RPAS provide different CLS. MC simulations are performed based on probabilistic distributions of aircraft performances, entry times and geographical distribution of aircraft. The safety levels are based on a conflict-risk model because the primary metrics are average number of conflicts and average conflict duration. The methodology is applied to one flight level of en-route airspace. The results provide restrictions to the number of RPAS that can jointly operate with conventional aircraft. Particularly, the TLS is quantified for four conventional aircraft and MC simulations provide the combinations of conventional aircraft and RPAS that fulfil the CLS. The same number of RPAS than conventional aircraft shows an increase over 90% average number of conflicts and 300% average conflict time.

The integration of Remotely Piloted Aircraft System (RPAS) in non-segregated airspace is one of the most demanding challenges that the aviation community must face in the years ahead. This article develops the flight-plan processing from a risk-based methodology. The risk-based methodology is underpinned by an in-depth safety analysis throughout the three temporary horizons of the Air Traffic Flow and Capacity Management system: strategical, pre-tactical and tactical. The flight-plan processing demands different measures depending on the temporary horizon. The measures mean geographical restrictions (airways or air corridors segregated for RPAS) and temporary restrictions (periods in which RPAS cannot operate). Both restrictions ensure that RPAS operation is safe and do not generate interactions with conventional aircraft. The last goal of this approach is to provide the required information to the RPAS operator based on the information available from the Network Manager (NM). The communication and information flow between the RPAS operator and the NM are detailed to validate flight-plan processing. If the initial flight plan is not affordable, the NM provides modifications during the flight-plan re-processing. The methodology is applied in the Spanish upper airspace. The results confirmed the validity and leeway of the flight-plan processing, although its implementation demands further improvements based on air traffic flow and path uncertainty. [ABSTRACT FROM AUTHOR]

In performance-based navigation (PBN) procedures with barometric vertical guidance, the effective vertical path angle (VPA) depends on the actual air temperature at the time of approach execution. A very low design temperature could result in an obstacle clearance height (OCH) higher than needed; hence, the airport throughput could be reduced when the cloud ceiling is below the OCH. Conversely, the design of a low temperature higher than is practical could lead to long periods in which the procedure cannot be used. The results of this research show that there is not much difference between the effective VPA for the different low temperatures studied. However, this slight difference, when obstacles penetrating the final approach surface (FAS) exist, usually leads to the approach minima being significantly different from each other. The objective of this study was to analyse the impact of the selected designed low temperatures in PBN procedures with barometric vertical guidance on the OCH/runway throughput and approach periods of use balance. Finally, guidelines on the selection of the minimum designed low temperature are proposed. [ABSTRACT FROM AUTHOR]

The required minimum separation distance between aircraft is believed to be one of the limiting factors on airspace capacity. In recent decades, aircraft separation rules have been modified by progressively shortening the required minimum separation distance. Following this trend in the coming years, a further reduction in the minimum separation distance would be expected. Still, a thorough assessment of the impact of this action on air traffic management performance should be carried out before investing in a reduction of separation minima. A Monte Carlo analysis of the en-route Spanish airspace shows that it is worth reducing the en-route minimum separation distance from 5 NM to 3 NM. This paper shows that a separation minima reduction will bring significant fuel savings, flight delay reduction, air traffic controller workload drop, and overall improvement of safety. [ABSTRACT FROM AUTHOR]

Designing and developing artificial intelligence (AI)-based systems that can be trusted justifiably is one of the main issues aviation must face in the coming years. European Union Aviation Safety Agency (EASA) has developed a user guide that could be potentially transformed as means of compliance for future AI-based regulation. Designers and developers must understand how the learning assurance process of any machine learning (ML) model impacts trust. ML is a narrow branch of AI that uses statistical models to perform predictions. This work deals with the learning assurance process for ML-based systems in the field of air traffic control. A conflict detection tool has been developed to identify separation infringements among aircraft pairs, and the ML algorithm used for classification and regression was extreme gradient boosting. This paper analyses the validity and adaptability of EASA W-shaped methodology for ML-based systems. The results have identified the lack of the EASA W-shaped methodology in time-dependent analysis, by showing how time can impact ML algorithms designed in the case where no time requirements are considered. Another meaningful conclusion is, for systems that depend highly on when the prediction is made, classification and regression metrics cannot be one-size-fits-all because they vary over time. [ABSTRACT FROM AUTHOR]

A Mid-Air Collision (MAC) is a fatal event with tragic consequences. To reduce the risk of a MAC, it is imperative to understand the precursors that trigger it. A primary precursor to a MAC is a loss of separation (LOS) or a separation infringement. This study develops a model to identify the factors contributing to a LOS between aircraft pairs. A Bayesian Network (BN) model is used to estimate the conditional dependencies of the factors affecting criticality, that is, how close the LOS has come to becoming a collision. This probabilistic model is built using GeNIe software from data (based on a database created from incident analysis) and expert judgment. The results of the model allow identification of how factors related to the scenario, the human factor (ATC and flight crew) or the technical systems, affect the criticality of the LOS. Based on this information, it is possible to exclude irrelevant elements that do not contribute or whose influence could be neglected, and to prioritize work on the most important ones, in order to increase ATM safety. [ABSTRACT FROM AUTHOR]

The integration of remotely piloted aircraft system in non-segregated airspace requires a significant effort and new methodologies to underway this challenge. This paper develops a methodology to assess the impact of remotely piloted aircraft system integration by applying safety metrics in tactical planning. This methodology builds five modules to simulate remotely piloted aircraft system introduction in a conventional-aircraft schedule: Base scenario, path modelling, conflict detection, temporary-blocking window and safety metrics. The safety metrics quantify the safety state of the operation by the number of conflicts, the conflict severity and the airway availability. This last safety metric represents a step forward in the decision-making process because it provides the airway risk-suitability to integrate remotely piloted aircraft system. Moreover, the temporary-blocking window underlies the airway availability metric. This concept provides temporary restrictions to the integration of remotely piloted aircraft system depending on the entry times of the conventional aircraft. Finally, this methodology is applied in an air traffic volume of the Spanish upper airspace. Different simulations were performed by introducing remotely piloted aircraft system covering every airway of the airspace. Results provided the temporary-blocking windows that specified the temporary restrictions to remotely piloted aircraft system introduction as a function of the airway flown by the conventional aircraft. Furthermore, the methodology appraised the airway availability characterising the airways depending on the risk impact by the remotely piloted aircraft system. [ABSTRACT FROM AUTHOR]

Continuous climb operation is an operational concept that allows airlines to perform an optimal departing trajectory avoiding air traffic control segregation requirements. This concept implies the design and integration of air traffic flows for the sake of safety performance. This paper designs a new conflict-detection air traffic control tool based on the blocking-area concept, characterises the conflict probability between air traffic flows and assesses the impact of continuous climb operation integration in a terminal manoeuvring area. In this paper, a conflict is set out by the infringement of vertical and longitudinal separation minima and coincides with the probability of air traffic control tool usage. Moreover, this research discusses two different approaches for the conflict-detection air traffic control tool: a static approach considering nominal continuous climb operations and landing trajectories, and a dynamic approach that assesses 105 continuous climb operations and landing trajectories. Finally, the air traffic control tool is implemented using Palma TMA data and proves that out of 11 intersections (between departing and landing routes), solely 4 generate vertical separation infringements. The conflict probability between continuous climb operations and arrivals is less than 10−5. Except for one intersection, that is roughly 10−2, similar to current air traffic control intervention designed levels. Therefore, results conclude the viability of the conflict-detection air traffic control tool and continuous climb operations integration. [ABSTRACT FROM AUTHOR]

Remotely-piloted aircraft systems (RPASs) present interesting and complex challenges for air traffic management. One of the most critical aspects of the integration of RPASs in non-segregated airspace is safety assessments. This paper lays out a methodology for estimating the minimum protection distance (MPD) that is required to avoid potential conflicts between RPASs and conventional aircraft. The MPD determines the final moment that air traffic control may instruct a RPAS to start climbing with a fixed rate of climb (ROC) to avoid separation minima infringement. The methodology sets out a conflict-resolution algorithm to estimate the MPD. It also models the impact of communication, navigation, and surveillance requirements on the MPD. The main difference between RPASs and conventional aircraft is that the former needs additional communication between the RPAS and pilot in the form of a required Comand and Control link performance (RLP). Finally, the authors carried out Monte Carlo simulations to estimate the value of the MPD only for the head-on encounter, which is the worst scenario. The results showed that the main factors affecting the MPD were RLP and ROC. By increasing RLP and decreasing ROC it was possible to reduce the MPD from 28 to 17 nautical miles; however, the variation in the MPD was not linear. [ABSTRACT FROM AUTHOR]

Air transport planning takes new technologies, strategies, and procedures into consideration when optimizing both trajectory and air traffic management. Continuous Climb operations (CCO) are new optimal departing trajectories that minimize fuel consumption, emissions, and noise levels within the vicinity of airports. In contrast with previous research, this paper does not focus on the optimization techniques of these procedures but on the estimation of novel separation minima. First, the authors present the CCO model: climbing structure, operational concept, and simulations. Second, Monte Carlo simulations are performed to obtain a large, statistically significant sample. The uncertainty of CCO trajectories is modeled taking several factors into account, such as aircraft type, mass, speed, positioning error, temperature, and wind. Mass is the factor that adds most uncertainty to climbing trajectories. Afterward, the authors develop a conflict-resolution algorithm to perform systematic analysis of separation minima. This algorithm has two goals: 1) to ensure that separation minima between aircraft pairs performing CCO are not violated throughout the departure, and 2) to dynamically calculate the on-ground separation between CCO. To the best of the authors' knowledge, this is the first time that an attempt has been made to quantify CCO separation minima. The results of the simulation confirm that the new CCO separation minima are larger than standard separation minima. [ABSTRACT FROM AUTHOR]

Given the ongoing interest in the application of Machine Learning (ML) techniques, the development of new Air Traffic Control (ATC) tools is paramount for the improvement of the management of the air transport system. This article develops an ATC tool based on ML techniques for conflict detection. The methodology develops a data-driven approach that predicts separation infringements between aircraft within airspace. The methodology exploits two different ML algorithms: classification and regression. Classification algorithms denote aircraft pairs as a Situation of Interest (SI), i.e., when two aircraft are predicted to cross with a separation lower than 10 Nautical Miles (NM) and 1000 feet. Regression algorithms predict the minimum separation expected between an aircraft pair. This data-driven approach extracts ADS-B trajectories from the OpenSky Network. In addition, the historical ADS-B trajectories work as 4D trajectory predictions to be used as inputs for the database. Conflict and SI are simulated by performing temporary modifications to ensure that the aircraft pierces into the airspace in the same time period. The methodology is applied to Switzerland's airspace. The results show that the ML algorithms could perform conflict prediction with high-accuracy metrics: 99% for SI classification and 1.5 NM for RMSE. [ABSTRACT FROM AUTHOR]

The expected growth of air traffic in the following decades demands the implementation of new operational concepts to avoid current limitations of the air traffic management system. This paper focuses on the strategic conflict management for four-dimensional trajectories (4DT) in free-route airspace. 4DT has been proposed as the future operational concept to manage air traffic. Thus, aircraft must fulfil temporary restrictions at specific waypoints in the airspace based on time windows. Based on the temporary restrictions, a strategic conflict management method is proposed to calculate the conflict probability of an aircraft pair (that intersects in the air) and to calculate temporary-blocking windows that quantify the time span at which an aircraft cannot depart because one conflict could occur. This methodology was applied in a case-study for an aircraft pair, including the uncertainty associated with 4DT. Moreover, a sensitivity analysis was performed to characterise the impact of wind conditions and speed control on the temporary-blocking windows. The results concluded that it is feasible to propose 4DT strategic de-confliction based on temporary-blocking windows. Although, uncertainty variables such as wind and speed control impact on the conflict probability and the size of the temporary-blocking windows. [ABSTRACT FROM AUTHOR]

Many civilian applications of commercial unmanned aircraft are being planned to operate in the years ahead. Several countries have developed their own framework to design the operation of unmanned aircraft and the different services that demand safe operation. This paper focuses on the European framework denoted as U-space which concludes with the joint integration of manned and unmanned aircraft in the airspace. U-space is a set of novel services and specific procedures designed to provide safe and efficient access into the airspace to the airspace users. U-space constitutes a management system to organise unmanned operations and provides relevant information to drone operators as well as manned aircraft, air navigation service providers and authorities. The understanding of associated hazards and risks to unmanned aircraft is a critical issue for their operation in complex and non-segregated airspaces. The safety assessment developed herein is crucial to identify safety indicators for U-space. In addition, the identification of safety indicators was used to identify gaps in U-spaces services that are not correctly covered by the U-space framework. Particularly, several safety indicators are identified that currently U-space services do not consider and can imply an increase in the operational risk of unmanned operations. [ABSTRACT FROM AUTHOR]