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Airborne Spacing:

Flight Deck View of Compatibility with

Continuous Descent Approach (CDA)

Eric Hoffman, Peter Martin, Thomas Pütz†, Aymeric Trzmiel*, Karim Zeghal

EUROCONTROL Experimental Centre

with the support of EUROCONTROL EATM & EVP programme of EC DGTREN

†Technishe Universität Berlin, Germany

*Steria, Issy-les-Moulineaux, France

European Organisation for the Safety of Air Navigation

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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

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Principles

� 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

References: PO-ASAS FAA/EUROCONTROL, ASAS circular ICAO, ANC 11 recommendations

Remain

Adjust speed

To maintain

current spacing

Merge

Adjust speed

To maintain

predicted spacing

Heading then

merge

Initiate direct then adjust

speed

To achieve then

maintain spacing

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Related studies

� Air perspective

� Model-based, human-in-the-loop and flight trials

� Kelly, Abbott (1984), Sorensen, Goka (1983), Williams (1983), Pritchett, Yankovsky (2000), Oseguera-Lohr, Lohr, Abbott, Eischeid (2002), Henley, Pywell (2005)

� Feasibility with limited impact on workload and improved inter aircraft spacing on final

� Ground perspective

� Model-based, human-in-the-loop

� Callantine, Lee, Mercer, Prevôt, Palmer (2005), Lee, Mercer, Martin, Prevôt, Shelden, Verma, Smith, Battiste, Johnson, Mogford, Palmer (2003), Hammer (2000), Krishnamurthy, Barmore, Bussink(2005), Penhallegon, Bone (2007)

� Enroute and terminal area

� Reduction of workload, improved spacing accuracy

� Link with continuous descent approach (CDA)

� Human-in-the-loop and flight trials

� Ren, Clarke (2007), Callantine, Homola, Lee, Mercer, Prevôt, Palmer, Smith (2007)

� Found to be compatible

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From past to present

� Full flight simulator experiment (March ‘05)

� Assess the effect of different reaction of preceding aircraft under spacing

� Assess feasibility of “heading then merge” instruction issued in TMA (with possible

change of target)

� Cockpit simulator experiment (December ‘05)

� Assess the managed speed mode used to acquire and maintain spacing with respect

to a target itself under spacing

� Assess the improved speed guidance

� Full flight simulator experiment (present)

� Confirm the feasibility of airborne spacing with speed and lateral managed modes in a

full-flight simulator

� Assess the compatibility of airborne spacing and continuous descent approach (CDA)

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Spacing task assistance

� Modes

� Two speed modes (merge, remain): selected and managed

� Two lateral modes (heading then merge): manual and automatic resume

� Displays

� ND: target aircraft information, spacing indications

� PFD: suggested speed

� MCDU: additional information

� Data inputs

� MCDU

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ASAS speed modes

ASAS Managed speed mode ASAS Selected speed mode

Selectedspeed modewith currentspeed value

Selectedspeed modewith selected

value

End spacing End spacing

PUSHFCU Speed KNOBPULL

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Spacing reached

ASAS lateral modes

ASAS MERGING TAMAK

ASAS Managed lateral mode ASAS Selected lateral mode

PUSHFCU HDG KNOBPULL

Resume turnautomaticallyperformed

Resume turnto be manually

performed

ASAS speed guidance

starts once merging

Spacing reached

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Cockpit interface (nominal)

Current spacing

(in seconds)

Required

spacing

Caution

(amber zone)

(2x4 seconds)

Lower spacing values

Higher spacing values

Spacing trend

(in 1 minute)

Spacing scale

Target aircraft

Spacingscale

Predicted Spacing

Pilots prompt

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A330 full flight simulator

� Technical University of Berlin

� Two configurations: training (JAR certified Level D) & research

(second host computer)

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Cross-track error

� Software FMS problem: cross-track error during turns

LOTAK

KIRED

MOKET

LFPO

FAO26

2924

2925

2926

2927

2928

2929

2930

95 105 115

Distance (NM)

Dis

tan

ce (

NM

)

Target TrajectoryTarget TrajectoryOwnship TrajectoryOwnship Trajectory

Flight Plan

* Not the same scale used for both axis

Maximal cross track-error of 0.45NM

(from model based study)

Cross-track errorMerge point (LOTAK)

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Experimental design

� Participants� Five crews of two pilots from European airlines during two days (four hours on the simulator each day).

� Environment� Paris South arrival flights, from cruise to final approach (~40 minutes flight time)

� Recorded scenario including ATC instructions and background traffic

� Target under spacing (not under conventional speed control)

� Two conditions: Optimised descent Vs. Non optimised descent

� Flight crew tasks� Automatic flight, checklist, operational flight plan, ATIS, briefing, and manual speed adjustments

� Perform two spacing task (in initial descent and in approach)

� Optimise the descent according to the experimental condition

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Airspace and scenarios

AW AE

FAO26 (4000ft)

KORAS (FL130)

AWAW AE

FAO26 (4000ft)

KORAS (FL130)

AW AE

VASOL (FL140)FL060FL060

APS

FL120FL100

CODYN (90s)

OKRIX (90s)

LOTAK (90s)

� Initial descent: “merge” CODYN or OKRIX (90s±5)

� Approach: “continue heading then merge” LOTAK (90s±5), until 2000ft

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Controller view

Scenario 1 Scenario 2

Ownship aircraft

Target aircraft

Target aircraft

Ownship aircraft

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Flight crew feedback (1/2)

� Spacing task

● Feasible and compatible from cruise until automatic disengagement at 2000ft

● More sensitive during approach phase than during initial descent (overlap with

flaps scheduling)

● Managed speed and lateral modes well accepted

● Compatible with CDA:

� Yes but in two steps (level off along the legs)

� Difficult to fly optimal descent (speed adjustments)

� Low level of workload for a good level of performance in both conditions (Non

optimised and optimised descent)

� Cockpit interface totally usable conveying useful information

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Flight crew feedback (2/2)

� Perceived benefits

� Increased situation awareness

� Reduced workload for both controllers and pilots (reduction of

communication)

� Better organised flows of traffic

� Optimised route structure (path, legs, and flight level)

� Slightly improved safety (because of reduction of communication)

� Perceived limitations

� Flight efficiency slightly degraded compared to todays’ situation

� Degraded situations (e.g. strong tail or cross wind)

� Compliance with company Standard Operational Procedure for flaps

scheduling

� Recovery procedure (e.g. unplanned behaviour of target aircraft)

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Spacing accuracy

� Spacing maintained accurately within the tolerance of 5s in initial descent (95% containment within ±2.1s)

� Cross-track error in approach led to larger deviation (95% containment within ±5s) and extreme values outside the tolerance

� No clear impact of the condition

Non optimised descent

Optimised descent

Mean Non optimised descent

Optimised descent

Mean

ApproachInitial descent

Spac

ing

devi

atio

n (s

)

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

Min for 95%

Max for 95%

Mean-STD

Mean+STDMean

Max

Min

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Unnecessary speed changesC

umul

ativ

e sp

eed

vari

atio

n (k

t)

0

10

20

30

40

50

60

70

80

90

100

110

120

Initial descent Approach phase

Non optimised descent

Optimised descent

Mean Non optimised descent

Optimised descent

Mean

Mean-STD

Mean+STDMean

Max

Min

� Overall cost of about 115kt (55kt during initial descent and 60kt during approach phase)

� Effect of cross-track error

� No clear impact of the condition

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Vertical profiles

Time

000:00:00 00:05:00 00:10:00 00:15:00 00:20:00 00:25:00 00:30:00 00:35:00 00:40:00

5000

10000

15000

20000

25000

30000

35000

Alt

itu

de

(fee

t)

Non optimised descent

Optimised descentScenario1

Scenario2

ApproachInitial descent

Alt

itud

e di

ffer

ence

(100

0fts

)

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

7

Scenario 1 Scenario 2 Mean Scenario 1 Scenario 2 Mean

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Conclusion

� Airborne spacing� Overall feedback globally positive and consistent with previous experiments� Found to be feasible from cruise until 2000ft, although more sensitive in approach phase

(overlap with flaps scheduling?)� Speed and lateral managed mode well accepted � Found compatible with a continuous descent approach (CDA) but in two steps

� Perceived benefits & limits� Benefits: increased situation awareness, reduced workload, better organised flows of traffic,

optimised route structure and slight increase of safety� Limits: flight efficiency slightly degraded, handling of unexpected events on final?

� Effectiveness� Spacing maintained 95% of time within tolerances (±5s) but values outside (±10s ) in approach

due cross-track error and different aircraft type� Cost induced ~ 115kt additional speed changes for the complete descent phase� Route structure and altitudes already optimised to allow a continuous descent from FL100

� Issues� Identify navigation requirements for airborne spacing (e.g. RNP RNAV)� Improve speed guidance to smooth speed profile in final approach

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Thank you for your attention!

Any question?