26-29 September 200526-29 September 2005 11

MILITARY AIRWORTHINESSMILITARY AIRWORTHINESSACCEPTABLE LEVEL of SAFETYACCEPTABLE LEVEL of SAFETY

Bob WojcikBob WojcikAir and Naval TechnologyAir and Naval TechnologyGeneral Dynamics CanadaGeneral Dynamics CanadaOttawa, Ontario, CanadaOttawa, Ontario, CanadaEmail bob.wojcik@gdcanada.comEmail bob.wojcik@gdcanada.com

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““If you are looking for perfect safety, you If you are looking for perfect safety, you will do well to sit on a fence and watch will do well to sit on a fence and watch the birds; but if you really wish to learn, the birds; but if you really wish to learn, you must mount a machine and become you must mount a machine and become acquainted with its tricks by actual trial.”acquainted with its tricks by actual trial.”

-Wilbur Wright, 18 September 1901-Wilbur Wright, 18 September 1901

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““There are two critical points in There are two critical points in every aerial flight – its beginning every aerial flight – its beginning and its end.”and its end.”

-Alexander Graham Bell, 1906-Alexander Graham Bell, 1906

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OutlineOutline

BackgroundBackground Safety DefinitionsSafety Definitions What is an Acceptable Level of What is an Acceptable Level of

Safety?Safety? How Safe is Safe?How Safe is Safe? Acceptable Level of Safety – Civil Acceptable Level of Safety – Civil

AircraftAircraft Acceptable Level of Safety – Military Acceptable Level of Safety – Military

AircraftAircraft Conclusion/RecommendationConclusion/Recommendation

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BackgroundBackground

Military authorities have always been Military authorities have always been interested in aviation safetyinterested in aviation safety

Many military authorities are Many military authorities are introducing formal Airworthiness introducing formal Airworthiness ProgramsPrograms

International Military Aviation International Military Aviation Authority ConferenceAuthority Conference 22-23 June 2004 22-23 June 2004Common theme – need for military Common theme – need for military

airworthiness regulatory authority airworthiness regulatory authority Many programs are modeled on civil Many programs are modeled on civil

aviation safety programsaviation safety programs Lack of military airworthiness Lack of military airworthiness

standards has led to reliance on civil standards has led to reliance on civil airworthiness standardsairworthiness standards

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Safety DefinitionsSafety Definitions

Concise Oxford Dictionary - Being safe, Concise Oxford Dictionary - Being safe, freedom from dangerfreedom from danger

MIL-STD 882 – Freedom from those MIL-STD 882 – Freedom from those conditions that can cause death, conditions that can cause death, injury, occupational illness, damage to injury, occupational illness, damage to or loss of equipment or property, or or loss of equipment or property, or damage to the environmentdamage to the environment

FAA System Safety Handbook – FAA System Safety Handbook – Freedom from all forms of harm. Freedom from all forms of harm.

British Standard 4778 – The freedom British Standard 4778 – The freedom from unacceptable risks of personal from unacceptable risks of personal harmharm

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What is an Acceptable Level of What is an Acceptable Level of Safety?Safety? A relative concept based on A relative concept based on

freedom from danger or riskfreedom from danger or risk Involves consideration of:Involves consideration of:

Severity of the effectSeverity of the effectCertainty of the occurrenceCertainty of the occurrenceReversibility of the effectReversibility of the effectKnowledge or familiarity of the risksKnowledge or familiarity of the risksVoluntary acceptance of the riskVoluntary acceptance of the riskCompensation for the riskCompensation for the riskAdvantages of the activityAdvantages of the activityRisks and advantages of the Risks and advantages of the

alternativesalternatives

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Safety Targets - DeterminationSafety Targets - Determination

Consider all consequences Consider all consequences including both risks and benefitsincluding both risks and benefits

Acceptance by both individuals and Acceptance by both individuals and societies in generalsocieties in general

Precedent of other regulatory Precedent of other regulatory organizationsorganizations

What is reasonable and practicalWhat is reasonable and practical

An acceptable level of safety could be defined as the point when the benefits outweigh the risks from either an individual or a society perspective.

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Regulatory AuthoritiesRegulatory Authorities

Airworthiness Regulatory Airworthiness Regulatory Authorities conduct risk-benefit Authorities conduct risk-benefit tradeoffs and decide what level tradeoffs and decide what level would be acceptable considering:would be acceptable considering:RequirementsRequirementsImpact on industryImpact on industryTechnology availableTechnology availableInput from stakeholders including Input from stakeholders including

public interest organizationspublic interest organizationsAction by other regulatory agenciesAction by other regulatory agencies

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What Is Safety?What Is Safety?

From a technical perspective From a technical perspective Safety is a design attribute which Safety is a design attribute which is part of the overall development is part of the overall development process. process.

Safety properties:Safety properties:Safety has no absolutesSafety has no absolutesSafety is non deterministicSafety is non deterministicAccident rates are generally very smallAccident rates are generally very small

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How Safe Is Safe?How Safe Is Safe?

Probability of Deaths Probability of Deaths per yearper year ActivityActivity

1 in 1001 in 100 five hours of solo rock five hours of solo rock climbing every weekendclimbing every weekend

1 in 5,0001 in 5,000 work in the UK coal work in the UK coal mining industrymining industry

1 in 50,0001 in 50,000 taking the contraceptive taking the contraceptive pillpill

1 in 500,0001 in 500,000 passenger in a scheduled passenger in a scheduled airlineairline

1 in 1 million1 in 1 million electrocution in the homeelectrocution in the home

1 in 10 million1 in 10 million Lightning in the UKLightning in the UK

Source: UK MOD “What is safety”UK MOD “What is safety”

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How Safe Is Safe? -TransportHow Safe Is Safe? -Transport

Mode of Mode of TransportTransport

Accident rate Accident rate per 100,000 per 100,000

hourshours

Fatality RateFatality Rate

Civil aircraft – Civil aircraft – airlineairline11

0.70.7 0.10.1

Civil aircraft - Civil aircraft - commutercommuter11

3.73.7 0.40.4

Rail TravelRail Travel22 0.060.06 0.020.02

MarineMarine22 1.91.9 0.080.08

Motor VehiclesMotor Vehicles22 0.530.53 0.010.01Source:

1 – Transport Canada 5 year average (1993 – 1997)

2 – DND/DGAEPM Airworthiness Risk Assessment Report (1996)

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Aircraft Accident Cause Aircraft Accident Cause FactorsFactors Technical CausesTechnical Causes

Airframe structural failureAirframe structural failureLanding gear failureLanding gear failureFireFireEngine failureEngine failureSystem failureSystem failure

Operational CausesOperational CausesWeatherWeatherControlled Flight Into TerrainControlled Flight Into TerrainUndershootUndershootOvershoot Overshoot

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Prevention – Technical Prevention – Technical Causes Causes Structural Failure (including Structural Failure (including

landing gear) – safe life, fail safe, landing gear) – safe life, fail safe, damage tolerancedamage tolerance

Fire – fire prevention and control Fire – fire prevention and control technologytechnology

Engine Failure - safe life, fail safe, Engine Failure - safe life, fail safe, damage tolerance, health damage tolerance, health monitoringmonitoring

System Failure – fail safe, system System Failure – fail safe, system safety assessment processsafety assessment process

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Prevention – System FailuresPrevention – System Failures

Largest technical cause of aircraft Largest technical cause of aircraft accidentsaccidents

Prevention of accidents due to Prevention of accidents due to system failures is one of the system failures is one of the primary concerns of civil primary concerns of civil airworthiness regulatory airworthiness regulatory authorities (FARs 23.1309, 25.1309 authorities (FARs 23.1309, 25.1309 & 29.1309)& 29.1309)

Severity CategoriesSeverity CategoriesCatastrophicCatastrophicHazardousHazardousMajorMajorMinor Minor No EffectNo Effect

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Acceptable Level of Safety – Acceptable Level of Safety – CivilCivil The accident rate for large civil The accident rate for large civil

transport aircraft has been steadily transport aircraft has been steadily declining since the early 60’s declining since the early 60’s

Generally an accident rate of 1 per Generally an accident rate of 1 per millionmillion flightflight hours has been hours has been considered acceptable for large considered acceptable for large civil passenger transport aircraftcivil passenger transport aircraft

Therefore the probability of a Therefore the probability of a serious accident should be not serious accident should be not greater than one per million flight greater than one per million flight hours (1 x 10hours (1 x 10-6-6))

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Acceptable Level of Safety – Acceptable Level of Safety – CivilCivil System failures account for 10% of System failures account for 10% of

accidents (probability of occurrence accidents (probability of occurrence of 1 x 10of 1 x 10-7)-7)

100 potential failure conditions that 100 potential failure conditions that could have a Catastrophic effectcould have a Catastrophic effect

Target average probability of Target average probability of occurrence established as 1 x 10occurrence established as 1 x 10-9-9 for for each failure condition with a each failure condition with a Catastrophic effectCatastrophic effect

General principleGeneral principle - - inverse inverse relationship should exist between a relationship should exist between a failure condition probability of failure condition probability of occurrence and severityoccurrence and severity

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Acceptable Level of Safety – Acceptable Level of Safety – CivilCivil

111010-1-11010-2-2

1010-3-3

1010-4-4

1010-5-5

1010-6-6

1010-7-7

1010-8-8

1010-9-9

Pro

bab

ilit

Pro

bab

ilit

yy

SeveritySeverity

UnacceptableUnacceptable

Note: Civil Transport CategoryNote: Civil Transport CategoryIndividual SystemIndividual System

AcceptableAcceptable

CatastrophicCatastrophic NegligibleNegligible

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Most military airworthiness Most military airworthiness authorities have not published authorities have not published military airworthiness design military airworthiness design standards standards

Reliance on civil regulatory material Reliance on civil regulatory material for military type certification and for military type certification and design change certification design change certification programsprogramsAirworthiness design standards (FARs, Airworthiness design standards (FARs,

CARs, JARs, etc)CARs, JARs, etc)Associated advisory material (FAA Associated advisory material (FAA

Advisory Circulars, RTCA DO-178B, RTCA Advisory Circulars, RTCA DO-178B, RTCA DO-254, SAE ARP4754, SAE ARP4761, DO-254, SAE ARP4754, SAE ARP4761, etc)etc)

Acceptable Level of Safety – Acceptable Level of Safety – MilitaryMilitary

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Acceptable Level of Safety – Acceptable Level of Safety – MilitaryMilitary Civil processes provides an Civil processes provides an

excellent basis for military aircraft excellent basis for military aircraft programsprograms

Civil target levels may be Civil target levels may be problematic for military aircraft, problematic for military aircraft, equipment or missionsequipment or missions

Military/Civil GapsMilitary/Civil GapsHandling qualitiesHandling qualitiesWeapons and storesWeapons and storesSelf defence suitesSelf defence suitesWartime operationsWartime operationsMilitary role/mission/task - operational Military role/mission/task - operational

necessitynecessityOperational and usage environmentOperational and usage environmentRapid advances of military technologyRapid advances of military technology

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Handling QualitiesHandling Qualities

Civil aircraft handling quality requirements Civil aircraft handling quality requirements do not adequately address military tactical do not adequately address military tactical role/mission/task requirements in the role/mission/task requirements in the intended operating environmentintended operating environment

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Weapons and StoresWeapons and Stores

Civil airworthiness standards have Civil airworthiness standards have no equivalent to military weapons no equivalent to military weapons and storesand stores

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Self Defence SuitesSelf Defence Suites

Military aircraft operate in a hostile Military aircraft operate in a hostile environment requiring the use of chaff, environment requiring the use of chaff, flares and other self defence technologyflares and other self defence technology

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Wartime OperationsWartime Operations

Military wartime operations include Military wartime operations include extremely hazardous missions under extremely hazardous missions under conditions of operational necessityconditions of operational necessity

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Military Military Roles/Missions/TasksRoles/Missions/Tasks

Many military roles/missions/tasks Many military roles/missions/tasks are unique and have no civil are unique and have no civil equivalentequivalent

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Environment and UsageEnvironment and Usage

Military aircraft often operate in a Military aircraft often operate in a harsh environment which is more harsh environment which is more severe than equivalent civil aircraft severe than equivalent civil aircraft types types

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Military TechnologyMilitary Technology

Military performance requirements Military performance requirements demand rapid advances in technology demand rapid advances in technology which may often be implemented before which may often be implemented before they are maturethey are mature

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Acceptable Level of Safety – Acceptable Level of Safety – MilitaryMilitary Application of civil standards must Application of civil standards must

be done with judgment, care and be done with judgment, care and forethoughtforethought

Difficult to separate military mission Difficult to separate military mission and airworthiness requirementsand airworthiness requirements

Traditionally military equipment Traditionally military equipment qualified to performance qualified to performance requirements rather than certified requirements rather than certified to minimum essential safety to minimum essential safety requirementsrequirements

No equivalent civil standards exist No equivalent civil standards exist for military unique equipmentfor military unique equipment

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Acceptable Level of Safety – Acceptable Level of Safety – MilitaryMilitary Civil airworthiness design Civil airworthiness design

standards are generally based on a standards are generally based on a specific aircraft category intended specific aircraft category intended for use within a defined for use within a defined operational environmentoperational environment

A higher accident rate should be A higher accident rate should be considered acceptable for military considered acceptable for military aircraftaircraft

Factor of 10 is often used in Factor of 10 is often used in comparing a military aircraft type comparing a military aircraft type with an equivalent civil aircraft with an equivalent civil aircraft typetype

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Acceptable Level of Safety – Acceptable Level of Safety – MilitaryMilitary

1010-9-9

Pro

bab

ilit

Pro

bab

ilit

yy

SeveritySeverity

UnacceptableUnacceptable

Note: Transport CategoryNote: Transport CategoryIndividual SystemIndividual System

AcceptableAcceptable

CatastrophicCatastrophic NegligibleNegligible

Military Military TransportsTransports

Civil Civil TransportsTransports

1010-3-3

1010-5-5

1010-7-7

1010-1-1

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CatastrophicCatastrophic NegligibleNegligible

Pro

bab

ilit

Pro

bab

ilit

yy

SeveritySeverity

UnacceptableUnacceptable

AcceptableAcceptableMilitary Military

TransportsTransports

Military Military JetsJets

Military Military HelicoptersHelicopters

Note: Military Aircraft TypesNote: Military Aircraft Types Individual SystemIndividual System

Acceptable Level of Safety – Acceptable Level of Safety – MilitaryMilitary

1010-9-9

1010-3-3

1010-5-5

1010-7-7

1010-1-1

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More flexibility required for military More flexibility required for military aviation than just defining level of aviation than just defining level of safety as acceptable / unacceptablesafety as acceptable / unacceptable

UK MOD - As Low As Reasonably UK MOD - As Low As Reasonably Possible (ALARP)Possible (ALARP)

MIL-STD 882 - Risk Index (defined as MIL-STD 882 - Risk Index (defined as a function of severity and probability a function of severity and probability of occurrence)of occurrence)

DND/CF TAM Risk definitionsDND/CF TAM Risk definitionsExtremely High Risk - Normally Extremely High Risk - Normally

unacceptableunacceptableHigh Risk - May be acceptableHigh Risk - May be acceptableMedium Risk - Should be acceptableMedium Risk - Should be acceptableLow Risk - AcceptableLow Risk - Acceptable

Acceptable Level of Safety – Acceptable Level of Safety – MilitaryMilitary

3333SeveritySeverity

1

Pro

bab

ility

Pro

bab

ility

Low RiskLow Risk

(acceptable)(acceptable)

Medium RiskMedium Risk

(should be acceptable)(should be acceptable)

High RiskHigh Risk

(may be acceptable)(may be acceptable)

Extremely High RiskExtremely High Risk

(normally unacceptable)(normally unacceptable)

CatastrophicCatastrophic NegligibleNegligible

Acceptable Level of Safety – Acceptable Level of Safety – MilitaryMilitary

1010-8-8

1010-2-2

1010-4-4

1010-6-6

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ConclusionConclusion

Acceptable Level of Safety is Acceptable Level of Safety is generally based on an acceptable generally based on an acceptable accident rate accident rate

The associated probability of The associated probability of occurrence for military aircraft occurrence for military aircraft types should be higher than the types should be higher than the equivalent civil aircraft typeequivalent civil aircraft type

Acceptable Level of Safety for Acceptable Level of Safety for military aircraft types may be military aircraft types may be based on a risk assessment processbased on a risk assessment process

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RecommendationRecommendation

Need a forum for military aviation Need a forum for military aviation authorities to discuss authorities to discuss airworthiness for military aircraft airworthiness for military aircraft typestypes

Defence industries need to present Defence industries need to present the problems associated with the the problems associated with the application of civil standards on application of civil standards on military aircraft programsmilitary aircraft programs

Closer cooperation/liaison between Closer cooperation/liaison between civil and military airworthiness civil and military airworthiness authoritiesauthorities

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““If we die, we want people to accept it. We are If we die, we want people to accept it. We are in a risky business, and we hope that if in a risky business, and we hope that if anything happens to us it will not delay the anything happens to us it will not delay the program. The conquest of space is worth the program. The conquest of space is worth the risk of life.”risk of life.”

-Astronaut Virgil I. Grissom, 27 January 1967-Astronaut Virgil I. Grissom, 27 January 1967

Paraphrased: Paraphrased: If we die, we want people If we die, we want people to accept it. We are in a risky to accept it. We are in a risky business, and we hope that if anything business, and we hope that if anything happens to us it will not delay the happens to us it will not delay the program. The program. The need for military aviationneed for military aviation is worth the risk of life.is worth the risk of life.

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