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CARE-ASAS Activity 3: ASM Estimating safe separations

CARE-ASAS Activity 3: ASM Estimating safe separations. Objective and tasks. Objective: Getting insight into safe separations for ASAS-based operational concepts, e.g. Autonomous Aircraft Tasks:

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CARE-ASAS Activity 3: ASM Estimating safe separations

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  1. CARE-ASAS Activity 3: ASMEstimating safe separations CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  2. Objective and tasks Objective: • Getting insight into safe separations for ASAS-based operational concepts, e.g. Autonomous Aircraft Tasks: • Identify hazards due to AA-OHA-identified mitigation measures and subsequent AA-OSED scenario refinement • Estimate safe separations for Autonomous Aircraft application as defined in AA-OSED CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  3. Hazards due to mitigating measures • Introduction of Safety Requirements identified by AA-OHA may lead to new hazards • Brainstorm: 55 (unanalysed) hazards / non-nominal situations, e.g. • Crew starts solving conflict before priority is determined • Everybody can listen in on VHF, even far away • Aircrew unaware of loss of communication (think it’s just quiet) • Confusion about position communicated by voice (no language to explain where you are since no waypoints in FFAS) • No time to update FMS during emergency, hence no intent data is transmitted • Aircrew decides not to leave FFAS in emergency (leaving may be more dangerous than continuing same flight path) CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  4. Estimating safe separations - content • Approach • Results • Conclusions CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  5. Estimating safe separations - approach Accident risk assessment methodology TOPAZ • Approach 1: for completely new concepts • Approach 2: variations on an evaluated concept • Use existing model (DCPN) for reference application that resembles target application • Risk assessment based on reference DCPN model, completed by uncertainty assessment • Risk assessment of target application, based on reference DCPN-based risk, and on effect of differences between target and reference operational concept CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  6. III II XFF* operational concept AA* operational concept AA operational concept I XFF* DCPN model From reference DCPN to AA concept CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  7. Bias & uncertainty of steps I and II • Method developed as part of TOPAZ methodology (Everdij and Blom, 2001) • Assess accident risk for Operational Concept in terms of • Model-based accident risk • The risk bias and uncertainty due to all assumptions adopted • Outline of method: • Identify all assumptions adopted • Assess all assumptions one by one on risk bias and risk uncertainty • During assessment of each assumption, take into account all previously assessed assumptions CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  8. Estimating safe separations - content • Approach • Results • Conclusions CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  9. Reference operational concept • Three candidates from TOPAZ information management system are ASAS-like • One of these three considers broadcast of aircraft intent information: Extended Free Flight (XFF) • RNP1 (VOR/DME) • ADS-B (state and intent) • Flight path conformance monitoring (own and other) • Conflict probe (between flight plans) • Short term conflict detection and resolution • No ACAS • Risk assessment of XFF limited to two opposite direction parallel lanes on same flight level: XFF* CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  10. S' S Encounter scenario considered • S: Distance between lane centrelines • S’: Separation minimum • First vary S, then S’ CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  11. Reference risk-separation curve CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  12. I: Differences XFF*-DCPN and XFF* • Numerical approximation assumptions • Identification by experts in the numerical evaluation of the XFF*-DCPN (7 x) • Parameter value assumptions • Identification by inspection of DCPN model description (70 x) • Model structure assumptions • Identification by experts of the XFF*-DCPN (23 x) • Non-coverage of hazards assumptions • Identification by experts of the XFF*-DCPN (22 x) • Sources: OHA, WP3 brainstorm, TOPAZ Information Management System CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  13. I: Risk effect CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  14. II: Differences XFF* and AA* • Navigation: XFF* has VOR/DME; AA* has GPS • Medium term conflicts: XFF* has CP at 5 min; AA* has priority assignment at 10 min, alert at 5 min, and uses R/T if necessary • Short term conflicts: AA* has independent surveillance alert • Consistency checks SA intent and state other a/c: XFF* has FPCM for other a/c and increases separation in case of alert; AA* does not have FPCM • Consistency checks SA intent and state own a/c: XFF* has FPCM for own a/c; AA* does not have FPCM • Use of CDTI: In XFF* crew are not required to monitor; in AA* they are • Emergency procedures: In AA*, a/c are alerted in case of emergency of own and other a/c, periodically broadcast position by R/T and leave FFAS. CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  15. II: Risk effect CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  16. XFF*-DCPN, XFF* and AA* results CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  17. III: Differences between AA* and AA Step from fixed route structure to free routes • Frequency of aircraft encounters is reduced significantly • Positive effect: risk figures improve linearly with number of encounters • Complexity of the traffic flow is increased significantly • No problem for pilots (Hoekstra et al, 2000) • Other effects • Semi-circular usage: opposite flying aircraft at different flight levels CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  18. Estimating safe separations - content • Approach • Results • Conclusions CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  19. Conclusions (1/2) • Model-based approach: gain insight into complex matter of estimating safe separation minima • Approach used followed two steps: • Select existing model similar to AA, evaluate model-based risk • Do a bias and uncertainty assessment that explains differences between model and AA concept • Results of model-based risk assessment: • XFF*-DCPN model based risk intersects target level of safety at S = 7 Nm, and S’ = 5 Nm • Results of bias and uncertainty assessment: • XFF* and AA* expected risk factor 1.6 and 3.5 higher than XFF*-DCPN model risk • 95% credibility interval: factor 5 up and down CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

  20. Conclusions (2/2) Improve operational concept • Combine complementary strong points of AA and XFF (e.g. FPCM, mitigating measures for key hazards) • If successful then improve RNP, e.g. RNP0.5 Extend DCPN model and evaluation • Develop DCPN model for XFF/AA concept • Reduce level of subjectivity of bias and uncertainty judgements First, evaluate outcome of these options with others CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001

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