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Remotely Piloted Aircraft (RPA) Postern Sense and Avoid (SAA)


OBJECTIVE: Identify approaches to achieving postern (rear-looking) sense and avoid (SAA) for remotely piloted aircraft (RPA). Develop the most promising and commercially viable candidate. Demonstrate performance and capability in a relevant environment. DESCRIPTION: Usually when people think of mid-air collisions (MAC), they envision encounters involving two aircraft approaching with head-on or converging trajectories, each aircraft in the other"s field of view (FOV). In such encounters the pilot of each vehicle can conceivably see the other aircraft in time to react and avoid disaster. However, Federal Aviation Administration (FAA) statistics indicate that 80 percent of MACs result from one aircraft overtaking another from behind. Of these, 30 percent of the faster moving aircraft approached between 0 to10 degrees of the slower aircraft"s tail nearly directly behind. These statistics were compiled on piloted aircraft. Because many RPA fly slower than piloted aircraft the incidence of overtakes is expected to rise as RPA airspace integration increases. Pilots are already concerned about overtaking and colliding with RPAs. RPAs fly slower are less maneuverable, have lower climb rate capability, are smaller on average than other traffic (e.g., RQ-7 Shadow), and sometimes are camouflaged to be hard to detect visually. RPAs create additional challenges to pilot SAA because RPA missions can involve hovering (e.g., M/RQ-8 Fire Scout) or circling in one location. However, some RPA are comparable in size and cruise airspeed to general aviation aircraft (e.g., MQ-9 Reaper) and able to climb to mid-level altitudes and higher. But these mid-to high-level altitudes are historically populated by much larger commercial airliners and military traffic flying at much higher speeds. During overtakes this size difference and high closure rate make it difficult to detect an RPA until it is too late to avoid a MAC. While the Traffic Alert and Collision Avoidance System (TCAS) and the Automatic Dependent Surveillance Broadcast (ADS-B) system mitigate the response time problem, not all aircraft are so equipped. Added to this risk is the tension created by current FAA rules-14CFR, Part 191, Section 91.113-which place the SAA burden on the overtaking pilot(s). From a pilot"s standpoint, RPA presence causes an elevated risk of an overtaking MAC. Current RPA SAA development efforts address forward-looking field of regard (FOR) requirements using multiple sensors. The purpose of the research proposed here is to explore methods/techniques to alleviate the overtaking MAC hazard described above for Group 2 through 4 RPA. To benefit both piloted aircraft and RPA, this system should not be dependent on the existence of an onboard forward SAA system. The objective is to explore the unique aspects of postern SAA, develop the most technologically promising and commercially viable candidate, and demonstrate the capability to be safe and effective. Known challenges include 1) airframe vibration and engine exhaust hindering valid detection and accurate position estimates (the goal is detect postern collision hazards not less than +/- 25 degrees in azimuth and elevation during day and night), 2) timely detection and tracking to provide not less than 30 seconds prior warning of aircraft with up to 120 knots overtake speed (the warning notification should contain as much information about the overtaking aircraft as possible (e.g., altitude, heading, airspeed), but relative azimuth and elevation as a minimum), and 3) sensor(s) selection to minimize size, weight, and power, and leverage forward-looking SAA sensor information (e.g., those which are omnidirectional) as appropriate. PHASE I: Identify approaches to attain postern SAA. Determine requirements and desired performance. Propose a candidate architecture. Identify equipment, hardware, and components as applicable. Begin algorithm development. Establish feasibility through modeling and simulation or other demonstration. PHASE II: Finalize the architecture, validate model, and mature algorithms/software. Apply design to fabricate a prototype. Demonstrate postern SAA through modeling and simulation or other demonstration. PHASE III: Goal is transition to operational use. Capability will be further matured to support/augment military SAA systems fielded or in development by producing a system of sensor(s)/algorithm(s)/hardware for a TBD platform. Application as a stand-alone system for piloted aircraft will also be considered. REFERENCES: 1. Aviation Safety,"Mid-air-collisions: the myth and the math: Mid-airs aren't always..,"James E. Lockridge, 1 April 2010. 2. Aircraft Owners and Pilots Association,"Collision Avoidance Strategies and Tactics,"Operations and Proficiency Safety Advisor No. 4. 3. Airpower Journal,"Unmanned Aerial Vehicles, The Force Multiplier of the 1990s,"Capt Brian P. Tice (USAF), Spring 1991. 4. Aviation, Space, and Environmental Medicine,"Midair Collisions: Limitations of the See-and-Avoid Concept in Civil Aviation,"C. Craig Morris, vol. 76, No. 4, April 2005. 5. Code of Federal Regulations, Part 91.113, Right-of-way rules: Except water operations.
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