JDC/MJC Feb12 1

Comparative wakeComparative wake--turbulence turbulence assessments and findings for the B747assessments and findings for the B747--8 8

J.D. Crouch & M.J. CzechJ.D. Crouch & M.J. Czech Boeing Commercial AirplanesBoeing Commercial Airplanes

WakeNet3WakeNet3--Europe Europe –– February 2012February 2012

JDC/MJC Feb12 2

Comparative wakeComparative wake--turbulence assessments turbulence assessments (overview)(overview)

A relative assessment of different airplane wakes Current system considered safe

Seek to assess relative safety of two operating aircraftBoth severity and likelihood

B747-8 Experience and Findings

Assessment approach

Flight testing and results

Safety Case, ICAO guidance, Safety Assessment Report (SAR)

More general approaches to wake assessment

JDC/MJC Feb12 3

33--view comparison of B747view comparison of B747--8 and B7478 and B747--400400

JDC/MJC Feb12 4

B747B747--8 passenger & freighter design weights8 passenger & freighter design weights

Design Weight 747-8 Passenger 747-400MTOW

(% increase)987,000(+8.5%)

910,000

MLW(% increase)

682,000(+5%)

652,000

Design Weight 747-8 Freighter 747-400FMTOW

(% increase)987,000(+8.5%)

910,000

MLW(% increase)

763,000(+15%)

666,000

JDC/MJC Feb12 5

B747B747--8 passenger & freighter design weights8 passenger & freighter design weights

Design Weight 747-8 Passenger 747-400MTOW

(% increase)987,000(+8.5%)

910,000

MLW(% increase)

682,000(+5%)

652,000

Design Weight 747-8 Freighter 747-400FMTOW

(% increase)987,000(+8.5%)

910,000

MLW(% increase)

763,000(+15%)

666,000

Weight increase suggests a potential increase in wake strength (& wake risk)

JDC/MJC Feb12 6

B747B747--8 Steering Group / Working Group structure8 Steering Group / Working Group structure

Air Safety Regulators

Aircraft Manufacturer

USA

Europe

Observers

Boeing 747-8Team

FAA Air Traffic

Organization

EUROCONTROLEASA

FAA AviationSafety

ICAO

ALPA

Air TrafficService Providers

W.Bryant (FAA)

JDC/MJC Feb12 7

B747B747--8 Working Group timeline8 Working Group timeline

2007 2008 2009 2010 2011

First WG meeting

ICAO state

lettersFlight testing

ICAO interim

guidance

Develop test planEstablish test requirements

Pre-flight CFD analysis

JDC/MJC Feb12 8

Equivalent level of safety approachEquivalent level of safety approach

Current Separation

Distance behind airplane (nm)

Measured vortex strength

(circulation)

Proposed Separation

Reference airplane : Solid line

New airplane : Dashed line

Basic assessment approach similar to A380

JDC/MJC Feb12 9

PrePre--flight CFD analysis of the B747flight CFD analysis of the B747--8 and B7478 and B747--400400

1. Start with wake survey at tail of aircraft2. Run Parabolized RANS CFD code to calculate wake evolution3. Extract relevant parameters at distances of interest

Tail survey(from wind tunnel

or full-airplane CFD)

Downstream assessment

(,b0 )

1

23

JDC/MJC Feb12 10

B747B747--8 wake flight testing8 wake flight testing

Compare B747-8 wake to a reference aircraft (B747-400)

Fresno, CA selected as test site based on weather, SNR and availability

JDC/MJC Feb12 11

FlightFlight--test procedurestest procedures

B747-8 and B747-400 flown sequentially in a circuit to enable pair-wise comparisons at approximately one wingspan above ground (most hazardous scenario) Environmental conditions carefully restricted (reasonably worst case)Airplane settings and trajectories carefully controlledFor each approach, measurements were made of airplane parameters, met conditions, and wake characteristicsVolpe Center supported ground measurements under contract to Boeing

LIDARLIDAR747747--88

747747--400400

Controlled Spacing

JDC/MJC Feb12 12

FlightFlight--test data analysistest data analysis

Flight testing complete: mid October 2010

Data provided to Working Group: late November 2010

Data analyzed by: FAA, EUROCONTROL, EASA, Boeing

Multiple analysis methods used

Multiple assessment approaches:Consider strength at fixed distanceConsider delta distance for equal strengthCompare encounter likelihood

JDC/MJC Feb12 13

Quantitative assessment of WVE severity: Wake strengthQuantitative assessment of WVE severity: Wake strengthStrength of vortices as a function of time (or distance) behind Strength of vortices as a function of time (or distance) behind aircraftaircraft

Data analyzed using many different approaches (representative reData analyzed using many different approaches (representative result)sult)

Similar result seen in analysis of rejected casesSimilar result seen in analysis of rejected cases

Following Distance (or Time)

Wak

e St

reng

th

B747-400B747-8

t

Following Distance (or Time)

Wak

e St

reng

th

B747-400B747-8

t

Following Distance (or Time)

Wak

e St

reng

th

B747-400B747-8

t

Following Distance (or Time)

Wak

e St

reng

th

B747-400B747-8

t

Example graph showing the B747-8 wake strength less than or equal to the B747-400

JDC/MJC Feb12 14

Example graph showing the B747-8 survival probability is less than or equal to the B747-400

Quantitative assessment of WVE likelihood: Survival Quantitative assessment of WVE likelihood: Survival probability and lifetimesprobability and lifetimes

VortexVortex--lifetime comparisons for B747lifetime comparisons for B747--400 and B747400 and B747--88

Probability of vortices lasting to a given time (or distance)Probability of vortices lasting to a given time (or distance)

Following Distance (or Time)

Sur

viva

l pro

babi

lity

B747-400B747-8

Following Distance (or Time)

Sur

viva

l pro

babi

lity

B747-400B747-8

JDC/MJC Feb12 15

FlightFlight--test data findingstest data findings

Flight test results in agreement with pre-flight CFD

Results show B747-8 wake strength less than or equal to the B747-400 at distances of interest

B747-8 vortices are closer together, resulting in more rapid descent and decay

747-8747-400

JDC/MJC Feb12 16

B747B747--8 wake8 wake--assessment documentationassessment documentation

Safety Assessment Report (SAR)

from B747-8 WG

BOEING PROPRIETARY DOCUMENT

Limited access on a need-to-know basis – with Proprietary Information Agreement

Contact: Terry L McVenes (BCA, Operational Regulatory Affairs)

Safety Casefrom B747-8 WG/SG

State Lettersfrom ICAO

PUBLIC DOCUMENT provided to ICAO

Available on request

Contact: Jeffrey Tittsworth (FAA, ATO)

PUBLIC DOCUMENT provided to ANSPs

JDC/MJC Feb12 17

Comparative wakeComparative wake--turbulence assessments turbulence assessments (overview)(overview)

A relative assessment of different airplane wakes Current system considered safe

Seek to assess relative safety of two operating aircraftBoth severity and likelihood

B747-8 Experience and Findings

Assessment approach

Flight testing and results

Safety Case, ICAO guidance, Safety Assessment Report (SAR)

More general approaches to wake assessment

JDC/MJC Feb12 18

The challenge of relative WVE risks assessmentsThe challenge of relative WVE risks assessmentsHow does an airplane modification translate into a change in WVEHow does an airplane modification translate into a change in WVE risk?risk?

Differences of interest may be overpowered by other factorsDifferences of interest may be overpowered by other factors

Wake Generation

Wake Evolution

Generating Airplane

Wake Encounters

Encounter Response

and Likelihood

Airplane Parameters Airplane Parameters

Environmental Factors

Airplane Parameters

Environmental Factors

Encounter Geometry

Encountering Airplane Airplane WVE risk

JDC/MJC Feb12 19

WVE risk assessment: Verification vs. RelevanceWVE risk assessment: Verification vs. RelevanceE

ase

of V

erifi

catio

n

Relevance to assessing WVE risk

a/p weight

Wake strength at distance

Compromise between what is easily verifiable and what is most relevant to describing safety risks

Initial wake characteristics

Wake encounters (function of number and scenario)

Low High

Low

Hig

h

JDC/MJC Feb12 20

Alternative approaches to WVE risk assessmentAlternative approaches to WVE risk assessmentHierarchy of methods to assess wake strength and encounter likelHierarchy of methods to assess wake strength and encounter likelihoodihood

1. Weight comparisons (e.g. current ICAO)MTOW, MLW

2. Estimated strength at distance (e.g. RECAT)Weight and span

(Need model for wake evolution, wing loading)

3. Predicted wake characteristics from CFDWeight, wing loading, near-field evolution, interaction w/ ground

(Need CFD tool and models for turbulence and instabilities)

4. Measured wake characteristics from flight (e.g. B747-8)Weight, wing loading, near-field evolution, far-field evolution, interaction with

ground – all at full scale

(Need suitable test site and measurement system. Influenced by environmental conditions, a/p operation and measurement limitations)

JDC/MJC Feb12 21

SummarySummary

A relative safety argument was used to assess the B747-8 wake-vortex encounter risks based on wake strength and wake lifetime

Documented in ICAO Safety CaseSupported by Boeing Safety Assessment Report

Future wake-assessment efforts should benefit from increased confidence in CFD and even simpler assessment methods