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Introduction to :

Wheel and Tire Failure :

Particular Risk Analysis

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WTF

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WTF statistics

Fatal

Accidents

Hull Loss

with no fa

talities

Debries e

ntered fuel ta

nk or e

ngine

Airfram

e damag

e

Decompressi

on0

10

20

30

40

1966 to 2005

1966 to 2005

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Learjet 60. Columbia Airport, USA19 Sept 2008

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Where do we start from ?

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The Four WTF PRA Models

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Four Models

GAS JET

Flailing Tread

Tread Shed

Rim Release

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Flailing Tread

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Flailing Tread Effects : A Whip.

• Mass : about 2 kg.• Speed : about 270 km/h

=>Energy : about 5 kJ

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Flailing Tread Model

• Only applies to extended MLG

• Why ?

• Impact : Aft part of the Main Landing Gear and the Braking System.

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Rim Release Model

Ref. Honeywell Report ERS-PROJ-WHAB-0000022 Dated 14 feb 2011.

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Rim Release Model

• Rim Release of retracted non-braked wheels do not need to be considered. Why ?

• Example : Retracted Nose Landing Gear Wheel.

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Frequency of occurrence

=> Why ? => Stress on NLG Rim when retracted : Low

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Tread Shed Model

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What to do with the PRA Models ?

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•USE CATIA AND THE DMU and a GOOD

Performance Computer.

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Next :

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What is a hit list ?

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Parameters for position

of PRA Model

Equipment Lost

Effect on System

Aircraft Level Function Lost

EFFECT ON AIRCRAFT

/CRITICALITY

HIT LIST EXAMPLE UERF Fragment impacting Fuel System

α

βFWSOV

Inability to isolate fuel to affected engine

FHA function 4.2.3.1 : Engine / Tire Burst Protection System

Inability to isolate fire following UERF

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Parameters for position

of PRA Model

Equipment Lost

Effect on System

Aircraft Level

Function Lost

EFFECT ON AIRCRAFT

α β FWSOV

How to fill-up the Hit List ?

? ? FHA

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• Asking questions, Communication, Exchange and Cross-Department Collaboration between the System Designer and the PRA Specialist with support of the DMU.

?

Source : Boeing & CATIA

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Quiz

• How many Wheel and Tire Failure different Models exist ?

• 3 ?• 5 ?• 6 ?• 4 ?

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Quiz

• How many Wheel and Tire Failure different Models exist ?

• 3 • 5 • 6 • 4

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Compilations of Hit-Lists

• Combines the effect of the PRA on the relevant ATAs together.

• Provides the consequence of the PRA at the Aircraft Level.

• When we hear talking about System Integration, this is one way to do System Integration.

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System Integration. WHY ?

• UERF on ATA 28 alone => Major• UERF on ATA 29 alone => Major• UERF on ATA 27 alone => Major

Put together => can be CAT.

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If you do not know what is impacted in CATIA ?

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WTF Tread Shed Trajectories

• Only trajectories to hit components.

• CATIA COMPASS => Model Manipulation.

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HOW TO MANIPULATE THE MODELS IN CATIA ?

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TREAD SHED MODEL APPLICABILITY

α

β

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ON THE DMU

• Starting from β = 0 deg, do all the analysis for • α to vary between 45 deg and 180 deg.– Alpha increments : 10 degrees.

– Refine when hit something (but no lower than 5 degrees increments)

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If we believe there is too many combinations of PRA WTF trajectories to be performed with α and β …

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Which WTF Model should we study first ?

Distribution of Main and Nose Tire Failure

Main Tire BurstMain Tire FlailingNose Tire BurstNose Tire Flailing

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•What happens to the results we found in the PRA analysis ?

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They Become Safety Requirements

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Example

The Main Fuel Pump shall be protected so that its functionality is maintained in case of a WTF

Tread Shed in the Lower Inner Wing Area.

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What to do with the Hit-List Analysis ?

• If it is critical => CAT => The Result of the Hit List Analysis will become a Safety Requirement.

• Example : From CATIA, we see that UERF hits the FWSOV => Propose to the Fuel System Designer to move the FWSOV outside of the UERF zone.

• HOW ?

• => Write a Safety Requirement :

<< The FWSOV shall be installed outside of the UERF area of its associated engine. >>

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Quiz

• What is the average speed of ejection for the Wheel Rim release model ?

• 20 m/s ?• 100 m/s ?• 400 m/s ?

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Quiz

• What is the average speed of ejection for the Wheel Rim release model ?

• 20 m/s • 100 m/s • 400 m/s

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Why the Requirement must be written in English ?

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• Some of our safety requirements need to be transmitted to our Suppliers.

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What becomes to the requirement ?

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Requirement Management

• DOORS is one of the way to manage requirements and to ensure they are properly addressed to the right persons / departments.

• A requirement not allocated to someone is useless…

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Why Do We Study WTF PRA ?

• Ensure Functionality of Critical Systems around the landing gear, the Wing and in the wheel wells.

• => Make Sure We do not loose safety-critical systems because of a WTF event.

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Last Quiz

• What was the cause of the Learjet 60 Accident ?

– Landing Gear Bay Design Deficiencies ?– Failure of Critical Systems in Wheel Well ?– Inadequacy of Learjet Safety Analysis ?– FAA failed to detect and correct the problem ?– All of the above ?

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Last Quiz

• What was the cause of the Learjet 60 Accident ?

– Landing Gear Bay Design Deficiencies – Failure of Critical Systems in Wheel Well – Inadequacy of Learjet Safety Analysis – FAA failed to detect and correct the problem – All of the above

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About the author :

Frederic CONTENOT, Chartered Engineer, is an international expert in Aircraft Safety.He has more than 25 years of experience in the Aerospace Industry.

Furthermore, he supported many major aircraft certification programs.

He is the founder and creator of Fiabtech Ltd :

Fiabtech Ltd provides engineering consultation, teaching and coaching to the aerospace industry, specializing- but not limited to – Safety Analysis on modern Passenger, Business jet aircrafts and UAVs.

The expertise Fiabtech Ltd provides is based on more than 25 years of experience in certification to FAR/CS 25 requirements of aircraft systems at major world class aircraft manufacturers.

Since 2005, Fiabtech Ltd developed a worldwide expertise in Particular Risk Analysis (PRA) and can provide expert assessments and advise on FAR 25 Certification Compliance for, but not limited to :

– Uncontained Engine Rotor Failure (UERF) : Frederic CONTENOT has world-renowned expertise in the field of UERF.

– Bird Strike

– Wheel and Tire Failure

– Survivability of Systems – Hydraulic Accumulator Burst

As these are complex subjects, please contact me for more information at: frederic@fiabtech.com