Safety Considerations for Operation of Different Classes of UAVs in the NAS Roland E. Weibel* and R. John Hansman, Jr.†Massachusetts Institute of Technology, Cambridge, MA 02139 Recognizing the significant effort underway to integrate UAV operations in the NAS, a preliminary hazard analysis was conducted for two critical hazards of UAV operation. Models were developed to describe UAV ground impact and midair collisions. Under several assumptions, a model of ground impact was used to calculate the UAV system reliability required to meet a target level of safety, for different UAV classes differentiated by mass. The model showed a significantly higher reliability required for high-mass UAVs, and a large variation in reliability required with population density, with a two order of magnitude increase over metropolitan areas. Midair collision risk was estimated in the vicinity of airways using a model of aircraft collisions based on the density of air traffic in those regions. There is a two order of magnitude difference in risk between on-airway and on-altitude operation and operation away from airways and off major flight levels. Therefore, there are potential operating strategies that can reduce the risk of UAV operation, such as procedural separation from high population and high traffic areas. There are also additional mitigation possibilities to further reduce the risk of integrating UAVs in the NAS. The integration strategies and mitigation requirements are likely to vary greatly for different classes of UAVs. Nomenclature Aexp = area of exposure d = distance traveled by air traffic within airspace segment ELS = expected level of safety MTBF = mean time Between failures resulting in ground impact Pfat | coll = probability of fatality given a potential collision Ppen = probability of penetration Pmit = probability of mitigation preventing a ground fatality ρ = population density t = time V = airspace volume I. Introduction he success of recent military deployment of Unmanned Aerial Vehicles (UAVs) in Iraq and Afghanistan has both raised public awareness of UAVs and proven their operational viability. This has led to an increasing demand for the ability to operate UAVs for a variety of applications over the United States. However, the current Federal Aviation Regulations did not anticipate the operation of unmanned aircraft in the NAS. Therefore, there are no regulations currently applicable to UAVs. Current UAV operation in the NAS has been limited to flights approved through a lengthy Certificate of Authorization process. T The lack of clear regulations has been a barrier to achieving benefits from potential commercial and civil operations. Recognizing this barrier, a significant effort is currently underway to integrate UAV operations into the National Airspace System (NAS)1. One fundamental requirement for operation in the NAS is to preserve the safety of the general public. Therefore, the implications for different classes of UAV operation should be examined based * Graduate Research Assistant, Department of Aeronautics & Astronautics, 77 Massachusetts Ave, Room 17-110, AIAA Student Member. † Professor, Department of Aeronautics & Astronautics, 77 Massachusetts Ave, Room 33-303, AIAA Fellow. American Institute of Aeronautics and Astronautics 1AIAA 3rd "Unmanned Unlimited" Technical Conference, Workshop and Exhibit20-23 September 2004, Chicago, IllinoisAIAA 2004-6421Copyright © 2004 by Roland E. Weibel. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.upon the requirement to operate at an equivalent level of safety. The purpose of this paper is to identify potential design requirements and approaches for integrating different classes of UAVs into the NAS that meet FAA system safety requirements. II. Range of Classifications & Capabilities In considering potential UAV operations in the NAS, it is important to recognize that the label “Unmanned Aerial Vehicle” can be applied to a broad range of vehicle types, configurations, and sizes. This broad spectrum is illustrated in Fig. 1 where several current UAVs are pictured, along with their locations on a logarithmic mass scale. For the purposes of this analysis, the following classes of UAVs are defined and primarily differentiated by mass: Micro, Mini, Tactical, Medium Altitude, and High Altitude/ UCAV (Unmanned Combat Air Vehicle.). While there is currently not a consensus on classifications for flight in civil airspace, these definitions are consistent with nomenclature used by both research and military communities. An estimation of the boundaries of each class in terms of UAV mass is also shown in Fig. 1. The maximum operating altitude of several current UAVs, was assembled from public sources2 and is shown in Fig. 2. There are are several divisions in potential operations between the classes. Micro UAVs are typically limited to short operating ranges, at low altitude, and weigh less than 1 lb.. Mini UAVs are operated at intermediate altitudes, and can potentially reach the boundary of controlled airspace at 18,000 ft. Mini UAVs are typically between 1 and 40 lbs. The tactical designation is borrowed from military UAV operation, and denotes a UAV that can sometimes be capable of over the horizon operation, and operated at low to intermediate altitudes. Tactical UAVs typically weight between 60 and 1,000 lbs. Medium and high altitude UAVs, as well as UCAV’s generally weigh more than 1,000 lbs. Medium altitude UAVs are typically operated around the region of Class A airspace, while high alttitude UAVs can potentially be operated above the majority of commercial air traffic. Aerovironment BlackWidow – 2.12 oz.BAE SystemsMicrostar – 3.0 oz.Sig Kadet II RCTrainer – 5 lbAerovironmentPointer – 9.6 lbBoeing/ Insitu Scaneagle – 33 lbAAI Shadow 200 – 328 lbBoeing X-45A UCAV – 12,195 lb (est)Bell Eagle Eye – 2,250 lb Allied Aero. LADF3.8 lbNOAA Weather Balloon 2-6 lbGen. Atomics – Predator B – 7,000 lbNorthrop-Grumman Global Hawk 25,600 lbUAV Weight (lb)0 1 10 100 1,000 10,000 100,000Micro Mini Tactical High Alt / UCAVMed AltFigure 1. Spectrum of Current UAVs Black WidowWaspAzimutPerseusMicrostarSheddonShed Mk3FoxProwlerIIGlobal HawkMini-VShadow 200PioneerCenturionDragon EyePathfinder+PointerEagle 1Eagle 2AladinLunaAltus IIGnat 2PredatorPredator BPhoenixBlack WidowWaspAzimutPerseusMicrostarSheddonShed Mk3FoxProwlerIIGlobal