page 2 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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
page 3 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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 its 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)
page 5 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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
page 6 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 From reference DCPN to AA concept XFF* operational concept AA operational concept AA* operational concept XFF* DCPN model II III I
page 7 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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
page 9 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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*
page 10 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 Encounter scenario considered S S' S: Distance between lane centrelines S: Separation minimum First vary S, then S
page 12 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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
page 14 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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.
page 16 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 XFF*-DCPN, XFF* and AA* results
page 17 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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
page 19 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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
page 20 CARE/ASAS Activity 3: ASM workshop Brétigny, 19 December 2001 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
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