Publications
Hazard alerting using line-of-sight rate
August 18, 2008
Conference Paper
Published in:
AIAA Guidance, Navigation, and Control Conf., 18-21 August 2008.
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Summary
This paper presents an analysis of an electro-optical hazard alerting system based on intruder line-of-sight rate. We use a recently-developed airspace encounter model to analyze intruder line-of-sight rate behavior prior to near miss. We look at a simple hazard alerting system that alerts whenever the line-of-sight rate drops below some set threshold. Simulations demonstrate that such an approach, regardless of the chosen threshold, leads to frequent false alerts. We explain how the problem of hazard alerting can also be formulated as a partially observable Markov decision process (POMDP) and show how such an approach significantly decreases the false alert rate.
Summary
This paper presents an analysis of an electro-optical hazard alerting system based on intruder line-of-sight rate. We use a recently-developed airspace encounter model to analyze intruder line-of-sight rate behavior prior to near miss. We look at a simple hazard alerting system that alerts whenever the line-of-sight rate drops below some...
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Applications of a macroscopic model for en route sector capacity
August 18, 2008
Conference Paper
Published in:
AIAA Guidance, Navigation and Control Conf. and Exhibit, 18-21 August 2008.
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Airspace capacity estimates are important both for airspace design and for operational air traffic management. Considerable effort has gone into understanding the complexity factors that reduce sector capacity by increasing controller workload. Yet no analytical means is available for accurately estimating the maximum capacity of an en route sector. The Monitor Alert Parameter (MAP) values that determine the operational traffic limit of en route sectors in the United States account only for workload from inter-sector coordination tasks. We propose a more complete sector capacity model that also accounts for workload from conflict avoidance and recurring tasks. We use mean closing speeds and airspace separation standards to estimate aircraft conflict rates. We estimate the mean controller service times for all three task types by fitting the model against observed peak traffic counts for hundreds of en route airspace volumes in the Northeastern United States. This macroscopic approach provides numerical capacity predictions that closely bound peak observed traffic densities for those airspace volumes. This paper reviews recent efforts to improve the accuracy of the bound by replacing certain global parameters with measured data from individual sectors. It also compares the model capacity with MAP values for sectors in the New York Center. It concludes by illustrating the use of the model to predict the capacity benefits of proposed technological and operational improvements to the air traffic management system.
Summary
Airspace capacity estimates are important both for airspace design and for operational air traffic management. Considerable effort has gone into understanding the complexity factors that reduce sector capacity by increasing controller workload. Yet no analytical means is available for accurately estimating the maximum capacity of an en route sector. The...
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Comparing convective weather avoidance models and aircraft-based data
August 4, 2008
Conference Paper
Published in:
89th ARAM Special Symp., 4 August 2008.
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The Convective Weather Avoidance Model (CWAM), developed in collaboration with NASA, translates convective weather information into a Weather Avoidance Field (WAF), to determine if pilots will route around convective regions. The WAF provides an estimate of the probability of pilot deviation around convective weather in en route airspace as a function of time, horizontal location, and flight altitude [1][2]. The results of the WAF can used to create reroutes around regions of convective weather where pilots are more likely to deviate. If reliable WAF information is provided to the cockpit and ground, pilot decisions may become more predictable, simplifying the task of air traffic control in convective weather. The improvement and validation of CWAM requires inference of pilot intent from flight trajectory data, which is challenging. The process currently involves laborious human review of the results of automated deviation detection algorithms. Both previous CWAM studies and a recent validation study [3] illustrate the difficulties and limitations of attempting to infer pilot intent from flight trajectory data. Furthermore, observed flight tracks may not correctly represent pilot preference. In some instances, pilots may have penetrated airspace that they would rather have avoided or they may have avoided airspace that was easily passable. In order to improve and assess the accuracy of the WAF, it is desirable to compare WAF predictions of pilot intent with direct evidence of the airborne experience during weather encounters in en route airspace, such as normal acceleration. To achieve this, a series of flights using a research aircraft was conducted. In the summer of 2008, four research flights (three on 17 July and one on 14 August) were flown in and around convective activity in the upper Midwestern United States to gather aircraft data that could be correlated to the WAF and other remotely-sensed weather data. The aircraft, a Rockwell Sabreliner Model 50 research aircraft (similar to the Sabreliner Model 40 production model) owned by Rockwell-Collins, flew through and around convective activity while recording on-board accelerations for comparison to the WAF deviation probabilities encountered along the flight trajectory. Aircraft state data, on-board weather radar images, video, photographs and pilot narrative from the cockpit were also collected. This paper briefly describes the CWAM model and WAF. Description of the data collection methodology is then presented. Following that section are descriptions of the flights comparing radar data from the flight deck with ground-based weather radar and the WAF. Visual observations and pilot narrative from the flight deck are also presented. Next, the normal acceleration data from on-board accelerometer data are compared with WAF. Finally, conclusions and suggestions for further study are presented.
Summary
The Convective Weather Avoidance Model (CWAM), developed in collaboration with NASA, translates convective weather information into a Weather Avoidance Field (WAF), to determine if pilots will route around convective regions. The WAF provides an estimate of the probability of pilot deviation around convective weather in en route airspace as a...
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Measuring the uncertainty of weather forecasts specific to air traffic management operations
August 4, 2008
Conference Paper
Published in:
89th ARAM Special Symp., 4 August 2008.
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In this paper, we develop a novel way to measure the accuracy of weather forecasts based upon the impact on air traffic flows. This method uses new techniques developed as part of the CWAM that consider the complicated interaction between pilots, air traffic controllers and weather. This technique, known as the blockage model (Martin et al., 2006), differentiates between minor deviations performed by pilots around convective weather and their larger deviations due to fully blocked air routes that require air traffic control interaction. This blockage model is being used by the automated Route Availability Planning Tool (RAPT) to predict route blockage for NYC departures. RAPT integrates the Corridor Integrated Weather Systems (CIWS) deterministic 0-2 hour forecasts of precipitation and echo tops into route specific forecasts of impact on air traffic in the congested east coast corridor. Applying the blockage model to the entire CIWS weather domain as a metric for scoring the performance of the forecast algorithms is shown to be an excellent approach for measuring the adequacy of the forecast in predicting the impact of the convective weather on air traffic operations.
Summary
In this paper, we develop a novel way to measure the accuracy of weather forecasts based upon the impact on air traffic flows. This method uses new techniques developed as part of the CWAM that consider the complicated interaction between pilots, air traffic controllers and weather. This technique, known as...
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Encounter modeling for sense and avoid deployment
May 5, 2008
Conference Paper
Published in:
2008 Integrated Communications, Navigation, and Surveillence Conf., 5-7 May 2008.
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Integrating unmanned aircraft into civil airspace requires the development and certification of systems for sensing and avoiding other aircraft. Because such systems are typically very complex and a high-level of safety must be maintained, rigorous analysis is required before they can be certified for operational use. As part of the certification process, collision avoidance systems need to be evaluated across millions of randomly generated close encounters that are representative of actual operations. New encounter models are under development that capture changes that have occurred in U.S. airspace since earlier models were developed in the 1980s and 1990s. These models capture the characteristics of small, General Aviation aircraft that may not be receiving Air Traffic Control services as well as typically larger aircraft that are squawking a discrete transponder code. Both models allow dynamic changes in airspeed, vertical rates, and turn rates in a way that was not possible previously. This paper describes the process used to construct the encounter models, how the models may be used in the development of sense-and-avoid systems for unmanned aircraft, and their application in an analysis of an electro-optical system for collision avoidance.
Summary
Integrating unmanned aircraft into civil airspace requires the development and certification of systems for sensing and avoiding other aircraft. Because such systems are typically very complex and a high-level of safety must be maintained, rigorous analysis is required before they can be certified for operational use. As part of the...
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Elementary surveillance (ELS) and enhanced surveillance (EHS) validation via Mode S secondary radar surveillance
April 25, 2008
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-337
Summary
Several applications of the Mode S data link are currently being implemented and equipage requirements have been issued in countries around the world. Elementary surveillance (ELS) and enhanced surveillance (EHS) applications have been mandated in Europe with full equipage of all aircraft in the airspace required by 2009. Exemptions to the ELS requirement include aircraft that will be out of service by 31 December 2009, and aircraft undergoing flight-testing, delivery, or transit into or out of maintenance bases. Transport type aircraft (defined as having a maximum take-off weight in excess of 250 knots) are to be equipped to support ELS and EHS. Exemptions to the requirements for EHS include those listed above for ELS and: a- fighter and training aircraft; b- rotary-wing aircraft; c- existing/older transport type aircraft undergoing avionics upgrades which will then support ELS/EHS; and d- aircraft types granted special exemptions (e.g., B1-B, B2-A, and B-52H bombers). [not complete]
Summary
Several applications of the Mode S data link are currently being implemented and equipage requirements have been issued in countries around the world. Elementary surveillance (ELS) and enhanced surveillance (EHS) applications have been mandated in Europe with full equipage of all aircraft in the airspace required by 2009. Exemptions to...
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A wind forecast algorithm to support Wake Turbulence Mitigation for Departures (WTMD)
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Turbulence associated with wake vortices generated by arriving and departing aircraft poses a potential safety risk to other nearby aircraft, and as such this potential risk may apply to aircraft operating on Closely Spaced Parallel Runways (CSPRs). Aircraft separation standards are imposed to mitigate this potential risk. The FAA and NASA are investigating application of wind-dependent procedures for improved departure operations that would safely reduce spacing restrictions to allow increased airport operating capacity. These procedures are referred to collectively as Wake Turbulence Mitigation for Departures (WTMD). An important component of WTMD is a Wind Forecast Algorithm (WFA) developed by MIT Lincoln Laboratory. The algorithm is designed to predict when runway crosswind conditions will remain persistently favorable to preclude transport of aircraft departure wakes into the path of aircraft on parallel runways (Figure 1). The algorithm has two distinct components for predicting the winds at the surface (33 ft) and aloft up to 1000 ft (the altitude by which an alternate form of separation would be applied by Air Traffic Control to aircraft departing the parallel runways, typically 15 degree or greater divergence in aircraft paths). The surface component forecast applies a statistical approach using recent observations of winds from 1-minute ASOS observations. The winds-aloft component relies on the 2 to 4 hour wind forecasts from NCEP's Rapid Update Cycle (RUC) model. The baseline version of the algorithm was developed and tested using data from St. Louis Lambert International Airport (STL). Algorithm performance was evaluated using 1-minute ASOS observations and crosswind component measurements taken from a dedicated Light Detection and Ranging (LIDAR) system. The algorithm was also demonstrated and evaluated at Houston George Bush International Airport (IAH). Use of the WFA is planned for 8 other airports deemed likely to derive significant benefit from WTMD procedures. The operational concept of WTMD for use by Air Traffic Control (ATC) includes additional decision levels beyond the WFA forecast. These include a check for VFR ceiling and visibility conditions, and final enablement by a human controller. More details concerning WTMD can be found in Lang et al. (2005) and Lang et al. (2007). A more complete description of the WFA is given in Robasky and Clark (2008). The early history of WFA development is detailed in Cole and Winkler (2004).
Summary
Turbulence associated with wake vortices generated by arriving and departing aircraft poses a potential safety risk to other nearby aircraft, and as such this potential risk may apply to aircraft operating on Closely Spaced Parallel Runways (CSPRs). Aircraft separation standards are imposed to mitigate this potential risk. The FAA and...
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Measuring the utilization of available aviation system capacity in convective weather
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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There is currently great interest in improving the ability to quantitatively assess how well U.S. Air Traffic Control (ATC) services are being provided as new weather-air traffic management (ATM) decision support capabilities are added. One of the three proposed metrics currently under study by the Federal Aviation Administration (FAA) and airlines is resource utilization, which has been defined as "the safe and efficient use of available airport or airspace capacity." Measurement of capacity utilization is particularly difficult during convective weather since storms cause capacity reductions in both en route and terminal airspace. In particular, en route capacity loss results in network congestion that cannot be readily characterized by scalar metrics. This paper proposes the use of (i) models for translating 3-D weather radar data into time-varying estimates of the capacity reductions in affected en route sectors, terminal airspace, and airports, together with (ii) automatically-generated, broad-area ATM strategies that utilize the time-varying estimates of airspace capacity and demand to determine optimal reroute strategies or, when necessary, minimally disruptive ground or airborne delay programs to assess how the available capacity could best been utilized. By comparing actual vs. optimal capacity utilization, one can assess how effective the actual weather-ATM system was at utilizing the available capacity. Examples of applying this methodology to severe convective weather events from 2005 and 2006 will be presented.
Summary
There is currently great interest in improving the ability to quantitatively assess how well U.S. Air Traffic Control (ATC) services are being provided as new weather-air traffic management (ATM) decision support capabilities are added. One of the three proposed metrics currently under study by the Federal Aviation Administration (FAA) and...
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Key research issues for near term operational use of integrated convective weather-ATM decision support systems
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Thunderstorm-related delays dominate the overall U.S. airspace delay statistics and continue to increase, even though a number of new weather information systems and air traffic management (ATM) decision support tools have been deployed since 1999. Operational decision makers must mitigate the network congestion that arises from rapidly varying capacity loss in both en route and terminal airspace. Improving decision making in such an environment requires explicitly considering airspace structure, network impacts, forecast uncertainty and pilot preferences for weather avoidance. To date, the NextGen initiative has focused on envisioning an operational concept and research agenda for 2025 where it is assumed that aircraft separation and weather avoidance is accomplished using a high degree of automation. In this paper, we consider research to achieve significant improvements in the near term (2010-2015) where aircraft separation is provided largely by controllers and hazardous weather avoidance is accomplished by pilots using visual cues, reports from other aircraft, on board weather radar and ATC advisories. We briefly review the current status of work in key areas and then suggest major near term initiatives. Key elements of the research program to be discussed include: 1. Translation of convective weather products into ATC impacts (including handling of uncertainty in the convective weather forecasts). Initial models for en route pilot avoidance of storms and sector capacity in convective weather have shown promising results, but clearly much more research is needed in this area. 2. Determining when and where available capacity was not appropriately utilized during convective events, based on both facility observations during storm events and computations of avoidable delay. Preliminary results suggest that much of today's delay is in fact avoidable. 3. Developing integrated weather-ATM decision support tools (DST) to enable decision makers to more fully utilize available capacity. The accuracy of contemporary convective weather forecasts is a key issue in the design of such systems. Initial operational experience with a departure decision support tool will be discussed to illustrate key points. 4. Explicitly considering the human side of convective weather ATM [e.g., how individuals make real time decisions in collaboration with other decision makers (e.g., ATC, airlines, dispatch, pilots)]. Recent results from field usage of convective weather decision support tools will be interpreted in the context of recent literature on how people actually make decisions and perform cognitively complex functions in demanding situations.
Summary
Thunderstorm-related delays dominate the overall U.S. airspace delay statistics and continue to increase, even though a number of new weather information systems and air traffic management (ATM) decision support tools have been deployed since 1999. Operational decision makers must mitigate the network congestion that arises from rapidly varying capacity loss...
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Evaluation of weather impact models in departure management decision support: operational performance of the Route Availability Planning Tool (RAPT) prototype
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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In this paper, the revised RAPT algorithm and display are described and evaluated. The fidelity of the RAPT operational model is assessed by comparing RAPT departure status with observed departure flows (i.e., trajectories, weather avoidance maneuvers and storm penetrations) on several days when convective weather SWAPs were in effect in New York. Real-time in-situ observations at RAPT facilities (described in a companion paper at this conference; Robinson, 2008), user feedback from RAPT playbacks and the REPEAT web site are used to support this post-event evaluation. For example, real time observations provide the time and operational rationale for a specific departure route closure identified in the traffic flow analysis. This information is necessary to identify closures or flow restrictions that are the result of factors outside of the current RAPT algorithm domain (e.g., traffic restrictions due to volume, downstream congestion, etc.). Real time observations are also used to identify specific times when critical, weather-related operational decisions were made. The RAPT guidance at these critical decision points is analyzed to determine if RAPT provided information that enabled (or could have enabled, had it been used) more timely or effective decisions. The effect of forecast uncertainty on RAPT performance is also examined, particularly in convective weather situations where the location, severity and operational impact were difficult to predict. Strategies that mitigated risks associated with forecast uncertainty are presented. These include the use of additional information provided in the RAPT display, such as echo top heights encountered along the departure route, to confirm or modify RAPT guidance and the consideration of the departure status of two or more adjacent routes to 'average out' variations in the departure status timelines.
Summary
In this paper, the revised RAPT algorithm and display are described and evaluated. The fidelity of the RAPT operational model is assessed by comparing RAPT departure status with observed departure flows (i.e., trajectories, weather avoidance maneuvers and storm penetrations) on several days when convective weather SWAPs were in effect in...
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