Wake Turbulence: do we Wake Turbulence: do we know enough to manage - - PowerPoint PPT Presentation

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Wake Turbulence: do we Wake Turbulence: do we know enough to manage - - PowerPoint PPT Presentation

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Wake Turbulence: do we Wake Turbulence: do we know enough to manage the know enough to manage the safety aspects? safety aspects? Bram Elsenaar co- co-ordinator ordinator of of Bram Elsenaar the European Thematic Network the European

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WakeNet2-Europe - Presentation Langley March 14, 2005

Wake Turbulence: do we Wake Turbulence: do we know enough to manage the know enough to manage the safety aspects? safety aspects?

Bram Elsenaar Bram Elsenaar co- co-ordinator

  • rdinator of
  • f

the European Thematic Network the European Thematic Network WakeNet2-Europe WakeNet2-Europe

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WakeNet2-Europe - Presentation Langley March 14, 2005

Introduction and background Present ruling, possible changes and benefits How to assess wake vortex safety ?

– Wake characterisation – Weather predictability – Encounter modelling – Probabilistic safety assessment – Monitoring rule change

Outline

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WakeNet2-Europe - Presentation Langley March 14, 2005

Introduction and background

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WakeNet2-Europe - Presentation Langley March 14, 2005

EUROWAKE near field vortex WAVENC encounter modeling M-FLAME

  • n board detection

C-WAKE wake characterization S-WAKE safety assessment AWIATOR minimizing by design I-WAKE

  • n board detection

WakeNet

WakeNet 2- Europe

European wake vortex related programs

WakeNet - USA

FAR-WAKE Fundamental aspects ATC-WAKE ATM implementation

STILL ACTIVE

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WakeNet2-Europe - Presentation Langley March 14, 2005

What’s the problem?

Flying aircraft generate a wake of two counter rotating vortices (like

horizontal ‘tornado’s’) – their initial strength depends roughly on the lift and wing span – they are transported by the wind – they normally descent but may stall or rebound for specific atmospheric conditions and near the ground – they decay due to atmospheric turbulence but persist for long time in quiet weather

When a following aircraft enters a wake, it may result in a severe

upset (bank-angle, sink rate)

Hence ICAO has made rules that prescribe the minimum separation

distances

These rules put a limit to airport capacity

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WakeNet2-Europe - Presentation Langley March 14, 2005

Present ruling, possible changes and benefits

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WakeNet2-Europe - Presentation Langley March 14, 2005

Present (ICAO) ruling (simplified)

For VFR conditions separation is determined by the

pilot / air traffic controller with the ‘runway occupancy time’ (ROT) as a minimum

For IFR conditions separation distances (in excess of

the radar separation of 2.5 nm) are prescribed by the ATC controller applying rules based on aircraft weight categories for leading and follower aircraft

Closely spaced parallel runways (CSPR) are treated as a

single runway for separation distances when the runways are less than 2500 ft apart

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WakeNet2-Europe - Presentation Langley March 14, 2005

ICAO ’s weight class dependend separation criteria

B747

Leading aircraft heavy > 136 t medium 7 - 136 t (small)/ light < 7 t heavy medium small Separation, miles

3 4 5 6

DHC-8 DHC-8 DHC-8 A320 A320 A320 B747

followed by No vortex-related separation for heavy aircraft

aircraft to scale A320 DHC-8

ICAO WV Separation Criteria

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Wake turbulence as loss-of-control factor: many reported incidents. . . . (Boeing: in Aviation Week, August 2002)

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WakeNet2-Europe - Presentation Langley March 14, 2005

. . . but wake turbulence is very rarely the cause of accidents

(ATM related accident rate’s from NLR Aviation Safety Data Base)

. . . but not ZERO!

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WakeNet2-Europe - Presentation Langley March 14, 2005

Experience with the present (ICAO or national) separation rules

There are regular incident reports of wake vortex

encounters, mostly non-hazardous

There are very few wake vortex induced accidents and

they occur almost exclusively for VFR conditions

Occasionally incident reports are filed for encounters

beyond the ‘safe separation distances’ e.g. for very quiet weather conditions with a weak tail wind Present separation distances are safe, possibly too conservative but not always; weather conditions are critical !

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WakeNet2-Europe - Presentation Langley March 14, 2005

Considering a change in the current practice

Would it be possible to reduce separation distances (by

rule change, depending on the weather conditions), while still maintaining the present level of safety?

Possible benefits are two-fold:

– tactical: reducing delays (whenever they occur) when the weather allows reduced separation distances – strategic: increasing the declared airport capacity (number of slots / hour)

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WakeNet2-Europe - Presentation Langley March 14, 2005

From simple to complex changes

Examples of ‘simple’ (rule) changes

– reduce the 2500 ft limit for closely space parallel runways to e.g. 1000 ft for smaller aircraft – apply a time based instead of a distance based separation criterion

Examples of more complex changes:

– weather dependent departures (using weather now-casting) – make the separation distances for closely spaced parallel runways dependent on the magnitude and direction of the cross-wind – make the single runway separation distances dependent on weather conditions (‘dynamic spacing’)

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Example (1): Wake turbulence mitigation for closely spaced parallel runway’s with displaced threshold’s as applied at Frankfort Airport (HALS/DTOP)

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WakeNet2-Europe - Presentation Langley March 14, 2005

Example (2): 2 Modes of Operation (ICAO / ATC-Wake) depending on weather

(from European ATC-wake program)

17:10 14:30 11:50

ICAO

ATC WAKE

08:20

ATC WAKE

ICAO

Arrivals : 2.5 NM Departures : 90 s Arrivals : 2.8 NM Departures : 100 s

07:29 Mode transition at 07:40 17:10 14:30 11:50

ICAO

ATC WAKE

08:20

ATC WAKE

ICAO

Arrivals : 2.5 NM Departures : 90 s Arrivals : 2.8 NM Departures : 100 s

07:29 Mode transition at 07:40

Brussels – 25 L / 25 R HMI for the Approach Controller Wake Vortex Vector on Radar Display

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Benefits: some numbers

EU estimates: Air Traffic delays cost 62 € per minute ;

total costs in 2002 : 700 M€ - 1000 M€ ( from EUROCONTROL Performance Review Report 6 )

NASA study on Dallas/FortWorth airport (independent runways)

indicates 8% capacity increase for weather dependent Wake Vortex Warning System

US Business Case Study indicates very favourable cost / benefit

ratio’s for Wake Vortex Advisory Systems (WVAS) in CSPR situations (sometimes as high as order of 100)

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If the benefits are so large, why hasn’t it been introduced?

Airport situation (runway layout, route structure, weather conditions) Regulations (assessment, on-line monitoring, incident reporting)

complexity safety capacity

ATM is already very complex! How to assess the safety?

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How to assess wake vortex safety ?

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Safety framework

In Europe ESARR4 sets requirements for safety

assessment (‘targeted level of safety’ approach)

wake encounters are very rare events, strongly weather

dependent: a probabilistic safety assessment is required

in European research programs building blocks for

such a safety assessment are developed and being refined e.g. – wake vortex characterisation including weather effects – research to define criteria for severe and non-sever encounters

for validation of risk assessment methodologies

incident reporting is essential

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WakeNet2-Europe - Presentation Langley March 14, 2005

Probabilistic wake and encounter modelling

(S-Wake, NLR)

A probabilistic risk assessment model for wake

turbulence: – tries to model the real world as truthful as possible – compares A/C response resulting from an encounter in the frame work of an ‘encounter severity classification’ – calculates the probability of a (catastrophic, hazardous, major, minor) accident / incident in the frame work of a ‘risk event classification’ – to be compared with a Target Level of Safety (TLS)

Rigor mathematical techniques are required to handle the

problem (to calculate for 10-9 TLS values)

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Scheme Risk Assessment Methodology

this presentation

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Typical cross flow velocities in a wake vortex (MEMPHIS Case 1107, AIRBUS 300)

Vortex core and peak velocity make the difference in decay

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Simple approximation with Kaden Vortex solely based

  • n aircraft characteristics

(same case as before; analysis by Elsenaar)

but modelling vortex cores is not trivial Simple models will do here

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WakeNet2-Europe - Presentation Langley March 14, 2005

Wake Vortex decay and life time for stable, turbulent and shear weather conditions (Memphis data, based on S-Wake analysis )

large variations in decay, vortex life times don’t fit easily in weather classes!

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Vortex life time: a function of Eddy dissipation rate and thermal stratification (results from LES calculations, DLR)

. . . there are more parameters than Eddy Dissipation rate ε like: Windshear S Thermal stratification N

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Frequency distributions (in %) of lateral transport of vortices due to crosswind (Analysis of the Memphis data for vortices out of ground effect by DLR) cross wind > 2 m/s: 252 cases

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Diurnal evolution of the wind speed profile on Tarbes Airport during WakeTOUL campaign (courtesy of DLR)

color code in m/s

measured predicted

Good enough ? A difference of a few m/sec in cross wind might matter !

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Example of actually observed safe and non-safe conditions as function of altitude over 24 hours (Frankfurt study; Konopka, DFS)

. . . in this case never safe

  • ver the entire height !
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Effectiveness of prediction of safe weather conditions (Frankfurt study by Konopka, DFS)

. . . for Frankfurt the benefit is small: too conservative . . . ?

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Comparison of prediction methods for wakes in ground effect: MEMPHIS case 1518, weak winds, stratification (from WN-USA / WN2-Europe Ground Effect Workshop)

VFS NEW VFS VORTEX P2P

. . . better modelling

  • f wakes in ground

effect might help but needs more validation !

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WakeNet2-Europe - Presentation Langley March 14, 2005

Accurate atmospheric measurements are essential: WTR – Wind Temperature Radar as installed at FraPort

Combination of Doppler-Radar for clear air measurements and Radio Acoustic Sound System (RASS) for measurements in bad weather

  • Measurement of wind (from 100m to 1500m altitude) with a precision of 0.5 m/s
  • and temperature (from 100m to 1000m altitude) with a precision of 0.5°C /100m

Manufacturer: Scintec AG, Tübingen, Germany

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Areas with dominating roll, yaw, and vertical accelerations (VFW614 behind VLTA ) S-Wake Study by Luckner (Airbus)

separation 5 Nm Winckelmans / Sarpkaya model

  • app. 80 % decay

Vortex core detail might matter here !

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Aircraft motion in wake encounter from flight simulation studies (S-Wake results, AIRBUS)

slow intercept from above (vertical intercept is 2 deg.) quick intercept from aside (horizontal intercept angle is 20 deg.)

. . . and here

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“Combined Roll-Control Ratio and Vertical Acceleration” criterion for Go-Around decision (S-Wake flight simulator results, AIRBUS)

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Determination of hazardous zone for wake vortex encounters (DLR, Hahn)

. . . . pragmatic, can be made to cover a ‘class of followers’ ; possibly somewhat conservative

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Probabilistic Wake Vortex Evolution Modelling (S-Wake, WAVIR, NLR)

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Encounter severity classification Results from WAVIR Monte Carlo type simulations (S-Wake, NLR)

Bank angle versus loss of height / encounter altitude is used as wake encounter severity metric

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WakeNet2-Europe - Presentation Langley March 14, 2005

Example of risk assessment for a B737 behind a B747 in ‘average’ weather conditions (S-wake, WAVIR, NLR)

Target Levels

  • f Safety (TLS)

Safe separation distance

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WakeNet2-Europe - Presentation Langley March 14, 2005

Introduction of new system and/or operational concept requires safety management approach

ATM ATM design design

Safety Safety assessment assessment

Safety regulation Safety regulation Incident reporting and monitoring Incident reporting and monitoring

e.g. NLR VORTEX, LHR reporting

e.g. WAVIR, VESA/ASAT

Not part of this presentation

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WakeNet2-Europe - Presentation Langley March 14, 2005

NLR – VORTEX: automated encounter detection from Flight Data Recordings processes involved in determining the wind vector Vg

aero inertial g

V V V r r r − =

Kalman Filter-Smoother (KFS) FDR

  • aerodyn. data

inertial data

  • nav. data

controls alpha calibration beta computation

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Possible WVE

  • ccurred midway

at 3000 ft

Example B737 landing approach altitude

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WakeNet2-Europe - Presentation Langley March 14, 2005

Example wind components

Peak in crosswind

component

Peak in vertical

wind component

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WakeNet2-Europe - Presentation Langley March 14, 2005

Example roll motion: bank and aileron

One single peak

both in roll and aileron

Bank angle

disturbance about +30 deg!

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WakeNet2-Europe - Presentation Langley March 14, 2005

London Heathrow: detected wake vortex encounters from NLR VORTEX FDR analysis (from S-Wake Study NATS / NLR)

Violet dots are detected (likely) encounters; Blue dots are radar trackings from the flight path’s of detected encounters

. . . encounters do

  • ccur
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WakeNet2-Europe - Presentation Langley March 14, 2005

Observed (relative) Inter-Arrival Times Haynie, George Mason University.

Atlanta Runway 27 357 observations, VMC

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Conclusions (1)

Establish sensitivities of encounter modelling

for details of the wake vortex and refine wake characterisation if required (e.g. decay)

Improve modelling for wakes in ground effect

and its validation

Push weather prediction to its limits, using the

most up-to-date measuring techniques and numerical weather forecast

Investigate (follower A/C class dependent !)

hazard definition

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WakeNet2-Europe - Presentation Langley March 14, 2005

Conclusions (2)

Improve and validate automated encounter

reporting from FDR analysis

Establish ‘current practice’ as (Airport

dependent?) ‘base line’

Agree on a safety assessment methodology

( who ? )

Organise ‘peer reviews’ to establish shortfalls

in wake vortex safety assessment

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WakeNet2-Europe - Presentation Langley March 14, 2005

To think about: If ‘uncertainty is piled upon uncertainty’, the

  • utcome will be worse than today; probabilistic

modelling, respecting all details and including proper validation, is the only promising answer.

Bram Elsenaar, to be discussed

It is likely easier to construct a safe system than to rigorously prove that the system is safe.

Jens Konopka, DFS, Langen 2004

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WakeNet2-Europe - Presentation Langley March 14, 2005

Thanks to all WakeNet2-Europe partners

NLR (co-ordinator) IFALPA (Vereinigung Cockpit) DLR THALES-AVIONICS DFS UCL NATS En-Route Ltd (NERL) EUROCONTROL AIRBUS (dep co-ordinator) UK MetOffice QinetiQ ONERA

. . . . . and to WakeNet-USA (FAA / NASA) ! WakeNet2-Europe is sponsored by the European Commision

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WakeNet2-Europe - Presentation Langley March 14, 2005

. . . and T H A N K Y O U for more information see the WebSite http://wwwe.onecert.fr/projets/WakeNet2-Europe