Proposed suas Safety Performance Requirements for Operations over People Brian Patterson Ted Lester Jeff Breunig Air Traffic Control Workshop 8 December 2016 Developed in Support of the: UAS EXCOM Science and Research Panel (SARP) Approved for Public Release; Distribution Unlimited. Case Number 16-3979 Non-Tech
Scope and Assumptions 2 Out of Scope suas flown within Visual Line of Sight (VLOS) and Extended VLOS (EVLOS) UAS larger than 55 pounds (25 kg) UAS faster than 200 mph Impact mitigation factors (e.g. parachutes, frangibility, etc.) Assumptions: The suas will not be flying within five miles of an airport without further mitigations The suas will be restricted to operations below 1,200 ft AGL (for the safety case) Considering both fixed and rotary suas
3 Risk Metric 3 rd Party Fatalities per suas Flight Hour 1 st Party Deriving direct economic benefit with considerable control over risk Aircrew and passengers on board aircraft 2 nd Party Deriving some economic benefit with some control over risk Aviation employees working at the time of the accident An individual on airport property 1 st Party Individuals 3 rd Party Deriving no economic benefit and no control over risk A person who is killed while in a residence, car, or other non-airport location 2 nd Party Individual 3 rd Party Individual This Methodology only looks at 3 rd Party Risk Approved for Public Release; Distribution Unlimited. Case Number XX-XXXX
suas Kinetic Energy Classifications 4 400 350 Bird strike requirements 300 250 Velocity (mph) 200 150 Bantam 100 50 Micro 0 0.5 Mini Limited 1,000 J 100 J 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Mass (kg) Kinetic Energy Micro 100 J Mini 1,000 J Limited 10,000 J Bantam 100,000 J
Risk Factors Risk Metric 3 rd Party Fatalities per suas Flight Hour 5 Risk Buckets Perceived operational risk of suas KE vs Population Density; Low, Medium, High suas Kinetic Energy (KE) Population Density Class Micro Mini Limited Bantam Weight 0.25 Kg (0.55 lb) 2 kg (4.4 lb) 9 kg (20 lb) 25 kg (55 lb) Kinetic Energy Class 0-100 J 100-1,000 J 1,000-10,000 J 10,000-100,000 J
Methodology 6 Event Risk Equation: TLS = Pk * Ps * PD * CA * LoF Population Density (PD) Crash Area (CA) Loss due to suas Internal Airworthiness Cause Loss due to Airworthiness suas system Failure, (e.g. Engine failure, C2, maintenance, operational errors, etc.) Loss due to Aerial Collision Shelter Factor (Ps) Lethality (Pk) Loss of Flight (LoF) for any reason Events Hazard Causes Loss due to suas External Operational Cause (e.g. Collision with other Aircraft, UAS etc.) Loss due to Fixed Obstacle (e.g. Collision with towers, trees, buildings, wires, ground, CFIT, etc.) Acceptable Risk Rate (TLS) TLS set for 3 rd party fatalities per flight hour Loss due to Environmental (e.g. Weather, Birds, etc.)
Scenarios 7 The scenario attempted to set up an average generic worse case situation to third party persons on the ground Looked only at cruise flight because; Was deemed to have the highest KE levels Least controllable operational mitigations 96 Total Scenarios (4x3x4x2) Four suas KE categories: Micro, Mini, Limited, and Bantam Three population density categories: Rural, Urban, and Open Air Assemblies Four suas starting altitudes: 300, 500, 700, and 1,200 (ft AGL) Two starting airspeeds (Micro 23/50, Mini 29/50, Limited 35/100, Bantam 70/200 (cruise/maximum MPH)
Target Level of Safety (TLS) 8 Event Risk Equation: TLS = Pk * Ps * PD * CA * LoF NTSB Historical Data Non-occupant fatalities due to civilian aircraft 5x10-7 ground (2 nd and 3 rd party) fatalities per flight hour DoD Range Safety Criteria for UAS 1x10-6 casualties per flight hour 1x10-7 fatalities per lifetime NRC POLICY ISSUE SECY-00-0077 5x10-7 fatalities per year General Aviation 7.5x10-5 accidents per flight hour 1x10-6 fatalities per flight hour Study of Non-Occupant Fatalities Removing 2 nd Party Fatalities Approximately 2.4 third party fatalities per year (5x10-8 per flight hour) Set TLS at 5x10-8 fatalities per flight hour
Lethality (Pk) 9 Event Risk Equation: TLS = Pk * Ps * PD * CA * LoF 1. suas terminal KE and impact angle 2. Coefficient of Restitution per impact angle KE At impact Impact Angle (IA) 3. Residual KE transfer to the human KE Transferred Lethality (Pk) 4. Lethality per residual KE (Pk) Approved for Public Release; Distribution Unlimited. Case Number XX-XXXX
Event Risk Equation: TLS = Pk * Ps * PD * CA * LoF 1. Most common shelters and construction models Shelter Factor (Ps) 2. Research on projectile penetration of shelters constructions 10 3. suas ability to penetrate the common shelters constructions 6. Derive a probability of suas strike given shelter (Ps) 5. Average third party personnel occupation per shelter type 4. suas probability of shelter penetration per shelter type
Crash Area (CA) 11 Event Risk Equation: TLS = Pk * Ps * PD * CA * LoF
Population Density (PD) 12 Event Risk Equation: TLS = Pk * Ps * PD * CA * LoF Difference between Rural and Urban, as defined by the US Census, is approximately 500 people per mile square. The SARP used LandScan Population Data, which is a world-wide approximate 1 km by 1 km grid of average (day/night) population counts that was produced by the Oak Ridge National Laboratory Those lists were then statistically analyzed to determine the Mean, Median, and 95th percentile population densities The SARP recommends adding a ½ nm buffer to the Urbanized Areas/Urban Clusters regions to define Urban areas for the purposes of suas BVLOS operations.
13 Event Risk Equation: TLS = Pk * Ps * PD * CA * LoF Target Level of Safety (TLS) 5x10-8 fatalities per flight hour Lethality (Pk) Shelter Factor (Ps) Crash Area (CA) PK Class Micro 1.00E-04 Mini 1 Limited 1 Bantam 1 Population Density (PD) PD People per mile 2 Rural 83 Urban 7,077 Open Air Assembly 2,589,988 Risk Allocation Loss of Flight (LoF) for any reason Proposed Maximum suas Loss of Flight for any reason per flight hour Rural Urban Open Air Micro None* None* 1.0E-03 Mini 0.10 1.0E-03 2.0E-7* Limited 0.02 2.0E-04 2.0E-7* Bantam 0.01 1.0E-04 2.0E-7* * None - No requirement needed * 2.0E-7 and 1.0E-7, Requirement exceeds that required by manned aircraft part 23. Suggest these aircraft meet part 23 requirements.
Proposed Requirements for suas Flight over People 14 Loss of controlled Flight (LoF) for any reason * None - No requirement needed * 2.0E-7 and 1.0E-7, Requirement exceeds that required by manned aircraft part 23. Suggest these aircraft meet part 23 requirements.
Comparison with Draft AC: 21-17b Design Standards for Type Design Approval of UAS UAS Risk Classification for the Probability of Catastrophic Failure 15
Conclusions 16 Event Risk Equation: TLS = Pk * Ps * PD * CA * LoF Lethality (Pk) suas KE levels go from no effect to lethal very quickly, making KE lethality essentially binary (Example: on average, the KE of a 9 kg suas is safe at 6 mph and 100% lethal at 20 mph, 14 mph separates a no effect impact from a 100% lethal impact) Above 300 ft AGL, most loss of flight suas are very close too, or at Terminal Velocity at impact, regardless of initial airspeed (hover, maximum, or cruse airspeed) and therefore at lethal KE levels (excepted Micros) The real risk from suas strike (from altitude) is whether a person gets struck or not, because if they are struck, it is most likely fatal. Shelter Factor (Ps) On average, the KE of the suas is not enough to penetrate most shelter construction materials, except for windows. The limited ability (lack of KE) of the suas to penetrate shelters makes shelters very effective at reducing population exposure, thereby restricting the effectiveness of KE as a risk factor. Crash Area (CA) suas have a very small crash areas resulting in very limited area of damage effect Population Density (PD) is the single overwhelming driver of risk for suas flight over people
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