1. 1 Airborne spacing in the terminal area: A study of non-nominal situations EUROCONTROL Experimental Centre European Organisation for the Safety of Air Navigation

2. 2 Starting point Motivation Improve the sequencing of arrival flows through a new allocation of spacing tasks between air and ground Neither “transfer problems” nor “give more freedom” to pilots … shall be beneficial to all parties Assumptions Air-air surveillance capabilities (ADS-B) Cockpit automation (ASAS) Constraints Human: consider current roles and working methods System: keep things as simple as possible Paris Orly, 2002, source: ADP

3. 3 Context (1/3) Development and refinement of spacing instructions and working methods Flight crew tasked by the controller to achieve then maintain a given spacing to a designated aircraft No modification of responsibility for separation provision New “spacing” instructions – not separation, not clearance Remain Adjust speed To maintain current spacing Merge Adjust speed To maintain predicted spacing Vector then merge Initiate direct then adjust speed To achieve then maintain spacing

4. 4 Context (2/3) Identification of required functional evolutions (air and ground) and route structure Aircraft under spacing Aircraft with target selected

5. 5 Context (3/3) Assessment of feasibility, benefits and limits Representative environment with very high traffic From cruise to final approach Controller, pilot and system perspectives Baseline With spacing Distribution of inter aircraft spacing at final approach fix 90 60120150180 Number of aircraft 22 23 24 25 26 27 Baseline Number of aircraft passing final approach fix (period 45min) With spacing Flown trajectories Baseline Flown trajectories With spacing

6. 6 From past to present However, everything was in nominal conditions… A series of prototyping sessions was conducted to investigate the use of airborne spacing under non-nominal conditions Feasibility and definition rather than data collection Focus on terminal area Situations investigated Mixed ASAS equipage Holding patterns Unexpected events (go-around, emergency, radio failure, spacing instructions not correctly executed)

7. 7 Experiment setup Generic TMA with two or three entry points feeding a single landing runway Traffic close to maximum landing capacity: 36 - 40 arrivals per hour with 20% heavys Departures not simulated but strategically separated Two controller positions Approach (“initial”, “pick up”) Final director (“intermediate”, “feeder”)

8. 8 Application to terminal area With spacing instructions (as defined), integration achieved on a point and aircraft shall be on lateral navigation How to integrate flows of aircraft with airborne spacing? How to delay or expedite aircraft under airborne spacing? Today (Paris Orly, 2002, source: ADP)

9. 9 Specific route structure FAF IAF Merge point Sequencing legs at iso distance for path shortening or stretching (vertically separated) Envelope of possible paths To expedite or delay aircraft while remaining on lateral navigation

10. 10 Typical airspace BOKET CODYN LOMAN MOTEK ODRAN OKRIX KAYEN LAURI RADON REDKO PONTY ZABOU FAO26 EPERN GOVIN MORET NASIG BOKET CODYN LOMAN MOTEK ODRAN OKRIX KAYEN LAURI RADON REDKO PONTY ZABOU FAO26 EPERN GOVIN MORET NASIG PONTY/MOTEKFL100 ODRAN/KAYENFL080 EPERN/GOVINFL060 ILS4000

11. 11 Mixed equipage

12. 12 Mixed equipage

13. 13 Typical airspace – Holding patterns BOKET CODYN LOMAN MOTEK ODRAN OKRIX KAYEN LAURI RADON REDKO PONTY ZABOU FAO26 EPERN GOVIN MORET NASIG BOKET CODYN LOMAN MOTEK ODRAN OKRIX KAYEN LAURI RADON REDKO PONTY ZABOU FAO26 EPERN GOVIN MORET NASIG PONTY/MOTEKFL100 ODRAN/KAYENFL080 EPERN/GOVINFL060 ILS4000

14. 14 Holding patterns

15. 15 Holding patterns A holding stack defined for each IAF Stacks located upstream from each leg Two flight levels for each sequencing legs Receiving aircraft from holding and airborne spacing for final integration found feasible and comfortable Traffic from holding very homogeneous Lack of accurate knowledge of aircraft actual exit of holding patterns forces delay in sequence order identification ASAS and its associated route structure found very effective to remove holding induced variability

16. 16 Go-around

17. 17 Go around Go-around occurred while in contact with tower Handling found not more difficult than with current practices Easy identification of where to re-integrate the aircraft Standard procedure defined Re-joining of one IAF May require cancelling spacing instructions and setting new ones Possible re-integration before the IAF (track parallel to the sequencing legs)

18. 18 Emergency

19. 19 Emergency Emergencies declared before the IAF Situation found not more difficult than today Speed difference vs. position in sequence Key steps Integration position decision Gap creation Vectoring Sequencing legs The emergency shall not be used as a target A “merge at least” may be issued for the emergency in case catching up the preceding aircraft Early speed reductions in upstream sectors to aircraft after the emergency

20. 20 Radio failure

21. 21 Radio failure Standard radio failure procedure defined Radio failure occurred before IAF Situation found not more difficult than today Early descent while on leg could create problems Overall same techniques as for emergency but with more margins due to un predictability of aircraft

22. 22 Incorrect spacing instructions Aircraft (under spacing) catching-up with its target Situations were not rated as serious cases by controllers Typical recovery procedure “cancel spacing” along with a speed reduction if appropriate re-select target (when not retained) and re-issue spacing instruction (generally “merge”) Worse case to be handled like a go-around “Continue heading then merge” correctly read-back but executed as “merge” Mistake detected quickly and found easy to handle by controllers Typical recovery procedure “cancel spacing, retain target” with speed (generally 220kt) to “non compliant” aircraft vector the aircraft on a track parallel to the sequencing legs new spacing instruction (generally “continue heading then merge”)

23. 23 Summary Mixed equipage Feasible Reduced workload and communications scalable Non equipped aircraft required more monitoring Holding patterns Airborne spacing for final integration found feasible and comfortable Unexpected events Less difficult than initially anticipated Similar to today’s operations Go-around, emergency and radio failure Identification of re-integration location is key point Spacing instructions not correctly executed Not rated as serious: quickly detected and easy to handle General principle to “isolate” the aircraft experiencing the problem (i.e. take it out of the sequence) not to act on the whole sequence

24. 24 A new RNAV route structure? A preliminary step to prepare implementation of airborne spacing A transition towards extensive use of P-RNAV A sound foundation to support further developments such as CDA (continuous descent) and 4D (target time of arrival) Beyond (or before)… 0 20 40 60 80 100 120 0 102030405060 Altitude (feet x100) Distance to final approach fix (NM) Baseline New route structure 0 20 40 60 80 100 Final Frequency occupancy (%) New route structure Baseline Approach