Karthik Krishnamurthy

Fast-Time Evaluations of Airborne Merging and Spacing in Terminal Arrival Operations

NASA researchers are developing new airborne technologies and procedures to increase runway throughput at capacity-constrained airports by improving the precision of inter-arrival spacing at the runway threshold. In this new operational concept, pilots of equipped aircraft are cleared to adjust aircraft speed to achieve a designated spacing interval at the runway threshold, relative to a designated lead aircraft. A new airborne toolset, prototypes of which are being developed at the NASA Langley Research Center, assists pilots in achieving this objective. The current prototype allows precision spacing operations to commence even when the aircraft and its lead are not yet in-trail, but are on merging arrival routes to the runway. A series of fast-time evaluations of the new toolset were conducted at the Langley Research Center during the summer of 2004. The study assessed toolset performance in a mixed fleet of aircraft on three merging arrival streams under a range of operating conditions. The results of the study indicate that the prototype possesses a high degree of robustness to moderate variations in operating conditions.

An analysis of merging and spacing operations with continuous descent approaches

Researchers at the NASA Langley Research Center are developing the airborne precision spacing (APS) concept to increase runway arrival throughput at capacity-constrained airports. Under APS operations, arrival capacity is increased by improving the precision of inter-arrival spacing at the runway threshold. Flight crews achieve this improved precision with the assistance of a new flight-deck system, which allows spacing operations to commence even while the aircraft and its lead are on different arrival routes to the runway. However, the increases in traffic volume that could be enabled by APS operations could also elevate noise concerns at busy airports. Noise- and fuel-efficiency concerns have independently motivated the air traffic management community to investigate continuous descent approaches (CDAs) as alternatives to traditional arrival route profiles. However, uncertainties associated with CDA operations can cause runway capacity to be sacrificed. For this reason, CDA routes have only been implemented during low-density traffic operations. In this paper, we report on current research into the integration of these two advancements, by employing APS operations to merge and space aircraft that are flying CDA arrival routes. Results obtained to date indicate that, while retaining the benefits of both techniques may be unachievable, APS operations can achieve narrow distributions of inter-aircraft spacing errors at the runway threshold for CDA routes. Analysis of the data also indicates that the spacing error distribution may be sensitive to inaccuracies in modeling the CDA trajectories for the aircraft and its lead.

USE OF TRAFFIC INTENT INFORMATION BY AUTONOMOUS AIRCRAFT IN CONSTRAINED OPERATIONS

This paper presents findings of a research study designed to provide insight into the issue of intent information exchange in constrained en-route air-traffic operations and its effect on pilot decision-making and flight performance. The piloted simulation was conducted in the Air Traffic Operations Laboratory at the NASA Langley Research Center. Two operational modes for autonomous flight management were compared under conditions of low and high operational complexity (traffic and airspace hazard density). The tactical mode was characterized primarily by the use of traffic state data for conflict detection and resolution and a manual approach to meeting operational constraints. The strategic mode involved the combined use of traffic state and intent information, provided the pilot an additional level of alerting, and allowed an automated approach to meeting operational constraints. Operational constraints applied in the experiment included separation assurance, schedule adherence, airspace hazard avoidance, flight efficiency, and passenger comfort. The strategic operational mode was found to be effective in reducing unnecessary maneuvering in conflict situations where the intruders intended maneuvers would resolve the conflict. Conditions of high operational complexity and vertical maneuvering resulted in increased proliferation of conflicts, but both operational modes exhibited characteristics of stability based on observed conflict proliferation rates of less than 30 percent. Scenario case studies illustrated the need for maneuver flight restrictions to prevent the creation of new conflicts through maneuvering and the need for an improved user interface design that appropriately focuses the pilots attention on conflict prevention information. Pilot real-time assessment of maximum workload indicated minimal sensitivity to operational complexity, providing further evidence that pilot workload is not the limiting factor for feasibility of an en-route distributed traffic management system, even under highly constrained conditions.

Autonomous aircraft operations using RTCA guidelines for airborne conflict management

A human-in-the-loop experiment was performed at the NASA Langley Research Center to study the feasibility of DAG-TM autonomous aircraft operations in highly constrained airspace. The airspace was constrained by a pair of special-use airspace (SUA) regions on either side of the pilots planned route. Traffic flow management (TFM) constraints were imposed as a required time of arrival and crossing altitude at an en route fix. Key guidelines from the RTCA airborne conflict management (ACM) concept were applied to autonomous aircraft operations for this experiment. These concepts included the RTCA ACM definitions of distinct conflict detection and collision avoidance zones, and the use of a graded system of conflict alerts for the flight crew. Three studies were conducted in the course of the experiment. The first study investigated the effect of hazard proximity upon pilot ability to meet constraints and solve conflict situations. The second study investigated pilot use of the airborne tools when faced with an unexpected loss of separation (LOS). The third study explored pilot interactions in an over-constrained conflict situation, with and without priority rules dictating who should move first. Detailed results from these studies were presented at the 5th USA/Europe Air Traffic management R&D Seminar (ATM2003). This overview paper focuses on the integration of the RTCA ACM concept into autonomous aircraft operations in highly constrained situations, and provides an overview of the results presented at the ATM2003 seminar. These results, together with previously reported studies, continue to support the feasibility of autonomous aircraft operations.

Alerting logic for multi-mode conflict detection and prevention in autonomous aircraft operations

NASA is developing a concept for far-term implementation of free flight in en-route airspace. The research concept introduces a new category of flight operations - autonomous flight rules (AFR). Properly trained flight crews of AFR-equipped aircraft possess the authority to autonomously plan and execute their preferred 4D trajectories, provided they accept responsibility for maintaining separation from traffic and conforming to ground-uplinked traffic flow management (TFM) constraints. Flight crews are supported in performing these tasks by decision-support automation integrated into the flight deck. Researchers at NASA Langley Research Center are developing a prototype of this decision-support system, called the autonomous operations planner (AOP). Since modern flight decks offer crews several levels of guidance automation, AOP employs multiple representations of the crews intentions for conflict detection. In order to be easy to use, responsive to crew-selected guidance options, and supportive of crew-initiated path planning, AOP must prioritize the different forms of intent and associated conflicts, and present the crew with an integrated yet intuitive picture of the current conflict situation. This paper describes the development of an alerting scheme that achieves these goals while meeting concept requirements for alerting time-horizons and the prevention of conflict proliferation. The alerting logic has been implemented in the Air Traffic Operations Laboratory at NASA Langley Research Center, and enables AOP to provide crews with appropriate alerting information when they operate their aircraft in any combination of guidance modes.