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MILITARY AIRWORTHINESS ACCEPTABLE LEVEL of SAFETY

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MILITARY AIRWORTHINESS ACCEPTABLE LEVEL of SAFETY Bob Wojcik Air and Naval Technology General Dynamics Canada Ottawa, Ontario, Canada Email bob.wojcik_at_gdcanada.com – PowerPoint PPT presentation

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Title: MILITARY AIRWORTHINESS ACCEPTABLE LEVEL of SAFETY


1
MILITARY AIRWORTHINESSACCEPTABLE LEVEL of SAFETY
  • Bob Wojcik
  • Air and Naval Technology
  • General Dynamics Canada
  • Ottawa, Ontario, Canada
  • Email bob.wojcik_at_gdcanada.com

2
  • If you are looking for perfect safety, you will
    do well to sit on a fence and watch the birds
    but if you really wish to learn, you must mount a
    machine and become acquainted with its tricks by
    actual trial.
  • -Wilbur Wright, 18 September 1901

3
  • There are two critical points in every aerial
    flight its beginning and its end.
  • -Alexander Graham Bell, 1906

4
Outline
  • Background
  • Safety Definitions
  • What is an Acceptable Level of Safety?
  • How Safe is Safe?
  • Acceptable Level of Safety Civil Aircraft
  • Acceptable Level of Safety Military Aircraft
  • Conclusion/Recommendation

5
Background
  • Military authorities have always been interested
    in aviation safety
  • Many military authorities are introducing formal
    Airworthiness Programs
  • International Military Aviation Authority
    Conference 22-23 June 2004
  • Common theme need for military airworthiness
    regulatory authority
  • Many programs are modeled on civil aviation
    safety programs
  • Lack of military airworthiness standards has led
    to reliance on civil airworthiness standards

6
Safety Definitions
  • Concise Oxford Dictionary - Being safe, freedom
    from danger
  • MIL-STD 882 Freedom from those conditions that
    can cause death, injury, occupational illness,
    damage to or loss of equipment or property, or
    damage to the environment
  • FAA System Safety Handbook Freedom from all
    forms of harm.
  • British Standard 4778 The freedom from
    unacceptable risks of personal harm

7
What is an Acceptable Level of Safety?
  • A relative concept based on freedom from danger
    or risk
  • Involves consideration of
  • Severity of the effect
  • Certainty of the occurrence
  • Reversibility of the effect
  • Knowledge or familiarity of the risks
  • Voluntary acceptance of the risk
  • Compensation for the risk
  • Advantages of the activity
  • Risks and advantages of the alternatives

8
Safety Targets - Determination
  • Consider all consequences including both risks
    and benefits
  • Acceptance by both individuals and societies in
    general
  • Precedent of other regulatory organizations
  • What 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.
9
Regulatory Authorities
  • Airworthiness Regulatory Authorities conduct
    risk-benefit tradeoffs and decide what level
    would be acceptable considering
  • Requirements
  • Impact on industry
  • Technology available
  • Input from stakeholders including public interest
    organizations
  • Action by other regulatory agencies

10
What Is Safety?
  • From a technical perspective Safety is a design
    attribute which is part of the overall
    development process.
  • Safety properties
  • Safety has no absolutes
  • Safety is non deterministic
  • Accident rates are generally very small

11
How Safe Is Safe?
Probability of Deaths per year Activity
1 in 100 five hours of solo rock climbing every weekend
1 in 5,000 work in the UK coal mining industry
1 in 50,000 taking the contraceptive pill
1 in 500,000 passenger in a scheduled airline
1 in 1 million electrocution in the home
1 in 10 million Lightning in the UK
Source UK MOD What is safety
12
How Safe Is Safe? -Transport
Mode of Transport Accident rate per 100,000 hours Fatality Rate
Civil aircraft airline1 0.7 0.1
Civil aircraft - commuter1 3.7 0.4
Rail Travel2 0.06 0.02
Marine2 1.9 0.08
Motor Vehicles2 0.53 0.01
Source 1 Transport Canada 5 year average (1993
1997) 2 DND/DGAEPM Airworthiness Risk
Assessment Report (1996)
13
Aircraft Accident Cause Factors
  • Technical Causes
  • Airframe structural failure
  • Landing gear failure
  • Fire
  • Engine failure
  • System failure
  • Operational Causes
  • Weather
  • Controlled Flight Into Terrain
  • Undershoot
  • Overshoot

14
Prevention Technical Causes
  • Structural Failure (including landing gear)
    safe life, fail safe, damage tolerance
  • Fire fire prevention and control technology
  • Engine Failure - safe life, fail safe, damage
    tolerance, health monitoring
  • System Failure fail safe, system safety
    assessment process

15
Prevention System Failures
  • Largest technical cause of aircraft accidents
  • Prevention of accidents due to system failures is
    one of the primary concerns of civil
    airworthiness regulatory authorities (FARs
    23.1309, 25.1309 29.1309)
  • Severity Categories
  • Catastrophic
  • Hazardous
  • Major
  • Minor
  • No Effect

16
Acceptable Level of Safety Civil
  • The accident rate for large civil transport
    aircraft has been steadily declining since the
    early 60s
  • Generally an accident rate of 1 per million
    flight hours has been considered acceptable for
    large civil passenger transport aircraft
  • Therefore the probability of a serious accident
    should be not greater than one per million flight
    hours (1 x 10-6)

17
Acceptable Level of Safety Civil
  • System failures account for 10 of accidents
    (probability of occurrence of 1 x 10-7)
  • 100 potential failure conditions that could have
    a Catastrophic effect
  • Target average probability of occurrence
    established as 1 x 10-9 for each failure
    condition with a Catastrophic effect
  • General principle - inverse relationship should
    exist between a failure condition probability of
    occurrence and severity

18
Acceptable Level of Safety Civil
Note Civil Transport Category Individual System
10-9
10-8
Probability
Acceptable
10-7
10-6
10-5
Unacceptable
10-4
10-3
10-2
10-1
1
Negligible
Catastrophic
Severity
19
Acceptable Level of Safety Military
  • Most military airworthiness authorities have not
    published military airworthiness design standards
  • Reliance on civil regulatory material for
    military type certification and design change
    certification programs
  • Airworthiness design standards (FARs, CARs, JARs,
    etc)
  • Associated advisory material (FAA Advisory
    Circulars, RTCA DO-178B, RTCA DO-254, SAE
    ARP4754, SAE ARP4761, etc)

20
Acceptable Level of Safety Military
  • Civil processes provides an excellent basis for
    military aircraft programs
  • Civil target levels may be problematic for
    military aircraft, equipment or missions
  • Military/Civil Gaps
  • Handling qualities
  • Weapons and stores
  • Self defence suites
  • Wartime operations
  • Military role/mission/task - operational
    necessity
  • Operational and usage environment
  • Rapid advances of military technology

21
Handling Qualities
  • Civil aircraft handling quality requirements do
    not adequately address military tactical
    role/mission/task requirements in the intended
    operating environment

22
Weapons and Stores
  • Civil airworthiness standards have no equivalent
    to military weapons and stores

23
Self Defence Suites
  • Military aircraft operate in a hostile
    environment requiring the use of chaff, flares
    and other self defence technology

24
Wartime Operations
  • Military wartime operations include extremely
    hazardous missions under conditions of
    operational necessity

25
Military Roles/Missions/Tasks
  • Many military roles/missions/tasks are unique and
    have no civil equivalent

26
Environment and Usage
  • Military aircraft often operate in a harsh
    environment which is more severe than equivalent
    civil aircraft types

27
Military Technology
  • Military performance requirements demand rapid
    advances in technology which may often be
    implemented before they are mature

28
Acceptable Level of Safety Military
  • Application of civil standards must be done with
    judgment, care and forethought
  • Difficult to separate military mission and
    airworthiness requirements
  • Traditionally military equipment qualified to
    performance requirements rather than certified to
    minimum essential safety requirements
  • No equivalent civil standards exist for military
    unique equipment

29
Acceptable Level of Safety Military
  • Civil airworthiness design standards are
    generally based on a specific aircraft category
    intended for use within a defined operational
    environment
  • A higher accident rate should be considered
    acceptable for military aircraft
  • Factor of 10 is often used in comparing a
    military aircraft type with an equivalent civil
    aircraft type

30
Acceptable Level of Safety Military
Note Transport Category Individual System
Military Transports
10-9
Probability
Acceptable
10-7
Civil Transports
10-5
Unacceptable
10-3
10-1
Negligible
Catastrophic
Severity
31
Acceptable Level of Safety Military
Note Military Aircraft Types Individual
System
Military Transports
10-9
Acceptable
Probability
10-7
Military Jets
10-5
Unacceptable
10-3
10-1
Catastrophic
Negligible
Severity
32
Acceptable Level of Safety Military
  • More flexibility required for military aviation
    than just defining level of safety as acceptable
    / unacceptable
  • UK MOD - As Low As Reasonably Possible (ALARP)
  • MIL-STD 882 - Risk Index (defined as a function
    of severity and probability of occurrence)
  • DND/CF TAM Risk definitions
  • Extremely High Risk - Normally unacceptable
  • High Risk - May be acceptable
  • Medium Risk - Should be acceptable
  • Low Risk - Acceptable

33
Acceptable Level of Safety Military
10-8
Low Risk (acceptable)
Probability
10-6
10-4
Extremely High Risk (normally unacceptable)
10-2
1
Catastrophic
Negligible
Severity
34
Conclusion
  • Acceptable Level of Safety is generally based on
    an acceptable accident rate
  • The associated probability of occurrence for
    military aircraft types should be higher than the
    equivalent civil aircraft type
  • Acceptable Level of Safety for military aircraft
    types may be based on a risk assessment process

35
Recommendation
  • Need a forum for military aviation authorities to
    discuss airworthiness for military aircraft types
  • Defence industries need to present the problems
    associated with the application of civil
    standards on military aircraft programs
  • Closer cooperation/liaison between civil and
    military airworthiness authorities

36
  • If we die, we want people to accept it. We are
    in a risky business, and we hope that if anything
    happens to us it will not delay the program. The
    conquest of space is worth the risk of life.
  • -Astronaut Virgil I. Grissom, 27 January 1967
  • Paraphrased If we die, we want people to accept
    it. We are in a risky business, and we hope that
    if anything happens to us it will not delay the
    program. The need for military aviation is worth
    the risk of life.

37
QUESTIONS
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