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Free Flight Airborne Separation: Challenges and Safety Concerns

The concept of Free Flight aims to reduce costs and enhance operational efficiency in aviation by allowing pilots to choose their own routing without central ATC control. However, this raises significant safety concerns as pilots may lack the time, training, and mental resources to manage airborne separation effectively. The study analyzes these risks, focusing on human factors, safety assessments, and conflict resolution techniques in a free flight scenario. Key findings highlight the potential difficulties of implementing such a system safely and the crucial role of advanced navigation technologies.

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Free Flight Airborne Separation: Challenges and Safety Concerns

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  1. “Free Flight with Airborne Separationwill result in an uncontrolled, dangerous junglewithout a firm central controlling elementsuch as ATC.” “Pilots haven’t got the time, the training nor the mental resources available tofunction as ATC on top offlying the aircraft.”

  2. NASA/FAA/RLD/NLRFree Flight study Jacco Hoekstra (hoekstra@nlr.nl) Ronald van Gent Rob Ruigrok

  3. Free Flight goals • Reduce Costs via user preferred routing • Horizontally • direct to destination • optimum speed • Vertically • optimum level • cruise climb • More capacity

  4. Operational concept • No ATC • Probe the limits for HF problems • All aircraft fully equipped • Linked via e.g. ADS-B • EFIS-CDTI • Full user preferred routing • Direct routing • Optimal cruise altitude

  5. 1997: Three sub-studies: • CONCEPTUAL DESIGNTool: Traffic Manager: Off-line simulations • Find a suitable base-line concept • SAFETY ANALYSISTool: TOPAZ (Traffic Organization and Perturbation AnalyZer) • Compare safety of Airborne Separation with safety ATC • MAN-IN-THE-LOOP EXPERIMENT phase ITool: Research Flight Simulator • Validation of concept with Man-in-the-Loop • Man Machine Interface Validation

  6. 1998: Four sub-studies: • CONFLICT GEOMETRY STUDYTool: Traffic Manager: Off-line simulations • Check critical geometries: wall, etc. • AVIONICS STUDYLiterature survey • Check requirements for RNP, ADS-B etc. • COST-BENEFITS & PERFORMANCETool: Traffic Manager: Off-line simulations • Costs of conflict resolution • MAN-IN-THE-LOOP EXPERIMENT phase IITool: Research Flight Simulator • Validation of PredASAS & mixed equipage

  7. 1999: Three activities: • DISSEMINATIONConferences, Web site, Contract report, RTCA, ICAO • Explain results obtained so far • DATA ANALYSIS phase II trials- Analysing data generated in phase II trials • DEVELOPMENT HUMAN INTERACTION EXPTool: Traffic Manager, Freesim & internet • Effect of competition

  8. 2000+: Current and future activities • HUMAN INTERACTION EXPERIMENTTraffic Manager, FreeSim, internet- High number of participants, humans vs models, competition • PHASE III FLIGHT SIMULATOR TRIALSNLR simulator, NASA Langley Simulations, HIE cfg(?)- How low can you go?From cruise to final incl. SUA, weather, RTA • Continue dissemination effortsWeb site, symposia, conferences, RTCA, SAE, (IF)ALPA

  9. Traffic & Experiment Manager

  10. Result Traffic Manager simulations • Resolution advisoriesSeveral concepts studied: • Altitude step • Cross product of speed vectors • Extended VFR rules (not implemented) • Variations of TCAS manoeuvres • Voltage potential • Co-operative manoeuvring vs. priority • Minimal bandwidth/HF: no intent in Conflict Detection

  11. Intruder’s protected zone Minimumdistance Heading distance Ownship Speed change Avoidance vector Intruder Conflict Detection & Resolution

  12. Complex Conflict geometries • ‘Wall’ scenarios, ‘super conflict’ (n = 4,8,10,12,16) and ‘crossing the street’

  13. Man-in-the-loop Simulation Configuration RFS AIRSIM TEM

  14. Traffic Symbol added to ND • Symbology on Navigation display based on data available via ADS-B • Track indicated with arrow shaped symbol instead of track line to avoid clutter • Label text selectable with de-clutter switches • Call sign added to label of traffic symbol for inter-trafficand crew communication

  15. Conflict Detection & Resolution • Symbology based on resolution algorithm • Provides insight into resolution • Colour indicates urgency:Amber = 3 - 5 minRed = 0 - 3 min(time to loss of separation)

  16. Navigation Display

  17. Man-in-the-Loop experimentHypotheses First explorative HF experiment, so probably using ‘simple’ Mk 1 system would yield: • Less than acceptable • Subjectively less safe • More workload Result: MMI problem areas

  18. Man-in-the-Loop experimentResults - Acceptability

  19. Man-in-the-Loop experimentResults- Subjective Safety

  20. Man-in-the-Loop experimentResults

  21. Task comparison Controlled vs. Free Flight

  22. Predictive ASAS Calculates which track, vertical speed and speed selections will result in a conflict within the look ahead time Predicts a conflict by the red/amber zone moving to the actual values Indications do not require pilot actions

  23. Predictive ASAS Don’t go indications: • Track • Vertical speed • Speed

  24. Preliminary conclusions PASAS • With predictive ASAS even conflict alerts could be avoided • Enhances situational awareness • Might provide solution without use of intent information for Free Flight!

  25. Mixed equipage ATM concepts • Flight Level division:Above FF level only equipped aircraft • Protected Airways:Controlled aircraft should stay on airways and have right of way • Fully Mixed:ATC uses longer ‘look ahead’ time, so equipped aircraft have effectively ‘right of way’

  26. 1998 NASA / FAA / RLD Results: Workload Airborne Subjective: Objective:

  27. 1998 NASA / FAA / RLD Results: Workload Ground F(2,8)= 9.7, P< .008

  28. 1998 Man-in-the-loop Conclusions • The future ATM design has to be chosen very carefully: • Full Mixed ATM condition is best from the pilot’s perspective • Protected Airways ATM condition is sensitive to equipage level (transition in time) • Flight Level ATC condition is most optimal from Air Traffic Controller’s perspective (Hilburn, Pekela) • The flight deck crew was able to handle higher traffic densities than the ground controller

  29. Current men-in-the-loop experiment:human interaction experiment • Logging into Traffic Manager via internet using downloadable FreeSim flight simulation program Goal: Test effect of • humans vs models • competition

  30. Airport on FF perspective: bad news(?) • Dramatic airspace capacity increase in FF airspace (en-route) => airports will be bottleneck (again)

  31. Airport perspective on FF: good news • ASAS equipment (especially traffic display) could facilitate more efficient use under IMC of: • airspace (curved, merging, station keeping) • runways (concurrent use of parallel and crossing runways) • taxiways (showing other a/c and ground vehicles) • => potential to increase sustained capacity

  32. More information • Web site:http://www.nlr.nl/public/hosted-sites/freeflight • Comprehensive report on overall studies 1997-1999Will soon be published. Check web site for downloads! • Demo sessions of human interaction experiment configuration will be announced on the website

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