Traffic Collision Avoidance Systems (TCAS) are safety-critical systems that are deployed on most commercial aircraft in service today. However, TCAS transactions were not designed to account for malicious actors. While in the past it may have been infeasible for an attacker to craft arbitrary radio signals, attackers today have access to open-source digital signal processing software like GNU Radio and inexpensive Software Define Radios (SDR). Therefore, this thesis presents motivation through analytical and experimental means for more investigation into TCAS from a security perspective. Methods for analyzing TCAS both qualitatively and quantitatively from an adversarial perspective are presented, and an experimental attack is developed in GNU Radio to perform an attack in a well-defined threat model. / Master of Science / Since 1993, the Federal Aviation Administration (FAA) requires that many commercial turbine-powered aircraft to be outfitted with an on-board mid-air collision mitigation system. This system is known as the Traffic Collision Avoidance System (TCAS) in the United States, and it is known as the Airborne Collision Avoidance System (ACAS) in other parts of the world. TCAS/ACAS is a type of safety-critical system, which means that implementations need to be highly tolerant to system failures because their operation directly affects the safety of the on-board passengers and crew. However, while safety-critical systems are tolerant to failures, the designers of these systems only account for failures that occur in a cooperative environment; these engineers fail to account for “bad actors” who want to attack the weaknesses of these systems, or they assume that attacking such a system is infeasible. Therefore, to demonstrate how safety-critical systems like TCAS/ACAS are vulnerable to such bad actors, this thesis presents a method for manipulating the TCAS/ACAS in the favor of a bad actor. To start, a method for qualitatively and quantitatively analyzing the system’s vulnerabilities is presented. Then, using Software Defined Radio (SDR), which is a free and open-source effort to combine the flexibility of software with the power of wireless communication, this thesis shows how an actor can craft wireless signals such that they appear to look like an aircraft on a collision course with a target.

The Small Aircraft Transportation System (SATS) is a partnership among various organizations including NASA, the FAA, US aviation industry, state and local aviation officials, and universities. The program objectives are intend to reduce travel times by providing high-speed, safe travel alternatives by making use of small aircraft and underused small airports throughout the nation. A major component of the SATS program is the Smart Landing Facility (SLF). The SLF is a small airport that has been upgraded to handle SATS traffic. One of the services needed at SLFs is air surveillance of the airspace surrounding it. This thesis researches the different surveillance techniques available for use at the SLFs. The main focuses of this paper are an evaluation of the Traffic Alert and Collision Avoidance System (TCAS) when used as a ground sensor at SLFs and the design of a Position and Identification Reporting Beacon (PIRB). The use of the TCAS ground sensor is modeled in Matlab and the results of that model are discussed. The PIRB is a new system that can be used in conjunction with the Automatic Dependent Surveillance-Broadcast (ADS-B) system or independently to provide position information for all aircraft using GPS based positioning. / Master of Science

The goal of this thesis is to improve pilot understanding of the Traffic alert and Collision Avoidance System (TCAS) by changing the Traffic Situation Display (TSD). This is supported by two objectives. The first objective is to create an integrated, realistic air traffic environment. This serves as an experimental platform for testing and evaluating future TCAS TSDs. The simulator environment includes a desktop flight simulator, background air traffic simulator, and intruder aircraft. The intruder aircraft uses seven dimensional waypoints to robustly follow trajectories and cause specific resolution advisories. Second, the relative benefits of, and potential concerns with, new TCAS TSDs are explored using a structured, iterative design process with subject matter ex- perts (SMEs). Incremental changes to the TSD were implemented into the simulator environment. SMEs evaluated the displays and potential points of confusion were identified. Several display features are discussed and implemented for future evaluations. These include boundary lines of TCAS variables depicted on the TSD and on a vertical situation display, speed lines which vary with the TCAS estimate of time to closest point of approach, and a prediction of the safe altitude target during a resolution advisory. Scenarios which may be confusing or misleading are discussed. These scenarios may be ameliorated or exacerbated by display features. This information is useful to guide both design and certification or operational approval and is a starting place for future TCAS experiments.

The Small Aircraft Transportation System (SATS) is a partnership between the FAA, the NASA, US aviation companies, universities and state and local aviation officials. The purpose of SATS is to develop a system to handle future increase in Air Traffic, reduce time-travel, develop automation in Air Traffic Control (ATC) and make better use of small aircraft and underused airports. The Smart Landing Facility (SLF) is an important part of the program. The SLF is a small airport upgraded with equipment to support SATS aircraft. Among the SLF equipment, SATS needs new detection equipment, and eventually automation. This thesis investigates different techniques to avoid data collision in aircraft radar responses, and to reduce delays between landings and take offs. First, the paper shows how and when the radar receiver can separate two overlapped radar responses. Second, to avoid transponders responses overlapping, requirements in terms of aircraft safety distance are computed, different conflicts in air traffic around the SLF are examined and a solution is proposed for each case. And finally, the thesis investigates how far SATS can go in developing an automatic ATC system and what the role of future human operator will be in ATC. / Master of Science

The Traffic alert and Collision Avoidance System (TCAS) is an aircraft collision avoidance system designed to prevent mid-air collisions. During an advisory, danger is imminent, and TCAS is assumed to have better, more up-to-date information than the ground operated air traffic control (ATC) facility. Following a TCAS RA is generally the safe course of action during an advisory. However, pilot compliance with RAs is surprisingly low. Results from a TCAS monitoring study show pilots are not complying with many TCAS advisories. As revealed by pilot-submitted Aviation Safety Reporting System (ASRS) reports, this noncompliance could be attributed, in part, to pilot confusion to TCAS operation as well as misunderstandings of the appropriate response to a TCAS issued advisory. This thesis details the development and evaluation of a TCAS training program intended to improve pilots' understanding of TCAS use for collision avoidance in a range of traffic situations. The training program integrated Demonstration Based and Event Based Training techniques. Its efficacy was analyzed in an integrated ATC-cockpit simulator study in which eighteen commercial airline pilots were asked to complete the TCAS training program and afterwards experienced twelve experimental traffic events. The trained pilots' performance was compared to the performance of 16 baseline pilots who did not receive the modified training. Overall, the training program did have a significant impact on the pilots' behavior and response to TCAS advisories. The measure Time Pilots First Achieved Compliance decreased with the trained pilots, as did the measure Autopilot Disconnect Time After RA Initiation. Trained pilots exhibited less aggressive performance in response to a TCAS RA (including a decrease in the measures Altitude Deviation Over Duration Of RA, Average Vertical Rate Difference, Maximum Vertical Rate Difference, and Maximum Vertical Rate). The measure Percent Compliance did not significantly vary between trained and baseline pilots, although trained pilots had a more consistent response in the traffic event with conflicting ATC guidance. Finally, on the post-experiment questionnaires, pilots commented on their increase in understanding of TCAS as well as an increase in their trust in the advisory system. Results of this research inform TCAS training objectives provided by the FAA as well as the design of TCAS training. Additionally, conclusions extend more broadly to improved training techniques for other similar complex, time-critical situations.

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