Airborne spacing in the terminal area A study

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

Starting point l Motivation l l 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 Paris Orly, 2002, source: ADP l Assumptions l l l Constraints l l 2 Air-air surveillance capabilities (ADS-B) Cockpit automation (ASAS) Human: consider current roles and working methods System: keep things as simple as possible

Context (1/3) l Development and refinement of spacing instructions and working methods l l l 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 To maintain current spacing Remai n 3 Adjust speed To maintain predicted spacing Merge To achieve then maintain spacing Adjust speed Initiate direct then adjust speed Vector then merge

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

Context (3/3) l Assessment of feasibility, benefits and limits l l l Representative environment with very high traffic From cruise to final approach Controller, pilot and system perspectives Flown trajectories Baseline Distribution of inter aircraft spacing at final approach fix. Baseline Number of aircraft passing final approach fix (period 45 min) 27 Number of aircraft With spacing Flown trajectories With spacing 26 25 With spacing 24 23 60 5 90 120 150 180 22 Baseline

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

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

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

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

Typical airspace EPERN FAO 26 BOKET LOMAN MORET NASIG GOVIN ZABOU ODRAN KAYEN RADON REDKO LAURI MOTEK PONTY CODYN OKRIX PONTY/MOTEK ODRAN/KAYEN EPERN/GOVIN ILS 10 FL 100 FL 080 FL 060 4000

Mixed equipage 11

Mixed equipage 12

Holding patterns 14

Holding patterns l l l l 15 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

Go-around 16

Go around l Go-around occurred while in contact with tower l Handling found not more difficult than with current practices Easy identification of where to re-integrate the aircraft l l Standard procedure defined l l l 17 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)

Emergency 18

Emergency l Emergencies declared before the IAF l Situation found not more difficult than today Speed difference vs. position in sequence Key steps l l Integration position decision Gap creation l l l 19 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

Radio failure 20

Radio failure l Standard radio failure procedure defined l Radio failure occurred before IAF l 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 l l 21

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

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

Beyond (or before)… l l 24 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 4 D (target time of arrival) Altitude (feet x 100) l 100 New route structure 80 60 Baseline 40 20 0 0 10 20 30 40 50 Distance to final approach fix (NM) Frequency occupancy (%) A new RNAV route structure? 120 100 Baseline New route structure 80 60 40 20 0 Final Approach 60