MILITARY AIRWORTHINESS ACCEPTABLE LEVEL of SAFETY
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Transcript MILITARY AIRWORTHINESS ACCEPTABLE LEVEL of SAFETY
MILITARY AIRWORTHINESS
ACCEPTABLE LEVEL of SAFETY
Bob Wojcik
Air and Naval Technology
General Dynamics Canada
Ottawa, Ontario, Canada
Email [email protected]
26-29 September 2005
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“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
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“There are two critical points in every
aerial flight – its beginning and its end.”
-Alexander Graham Bell, 1906
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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
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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
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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
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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
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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.
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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
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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
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How Safe Is Safe?
Probability of Deaths
per year
1 in 100
Activity
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”
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How Safe Is Safe? -Transport
Mode of
Transport
Accident rate
per 100,000
hours
0.7
Fatality Rate
3.7
0.4
Rail Travel2
0.06
0.02
Marine2
1.9
0.53
0.08
0.01
Civil aircraft –
airline1
Civil aircraft commuter1
Motor Vehicles2
0.1
Source:
1 – Transport Canada 5 year average (1993 – 1997)
2 – DND/DGAEPM Airworthiness Risk Assessment Report (1996)
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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
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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
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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
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Acceptable Level of Safety – Civil
The accident rate for large civil
transport aircraft has been steadily
declining since the early 60’s
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)
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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
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Acceptable Level of Safety – Civil
Note: Civil Transport Category
Individual System
10-9
10-8
Acceptable
10-7
10-6
10-5
Unacceptable
10-4
10-3
10-2
10-1
1
Catastrophic
Negligible
Severity
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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)
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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
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Handling Qualities
Civil aircraft handling quality requirements do
not adequately address military tactical
role/mission/task requirements in the intended
operating environment
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Weapons and Stores
Civil airworthiness standards have no
equivalent to military weapons and
stores
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Self Defence Suites
Military aircraft operate in a hostile
environment requiring the use of chaff,
flares and other self defence technology
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Wartime Operations
Military wartime operations include
extremely hazardous missions under
conditions of operational necessity
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Military Roles/Missions/Tasks
Many military roles/missions/tasks are
unique and have no civil equivalent
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Environment and Usage
Military aircraft often operate in a
harsh environment which is more
severe than equivalent civil aircraft
types
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Military Technology
Military performance requirements
demand rapid advances in technology
which may often be implemented
before they are mature
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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
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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
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Acceptable Level of Safety – Military
10-9
Military
Transports
10-7
10-5
Note: Transport Category
Individual System
Acceptable
Civil
Transports
Unacceptable
10-3
10-1
Catastrophic
Negligible
Severity
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Acceptable Level of Safety – Military
10-9
Note: Military Aircraft Types
Individual System
Military
Transports
Acceptable
Military
Helicopters
10-7
Military
Jets
10-5
10-3
10-1
Unacceptable
Catastrophic
Negligible
Severity
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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
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Acceptable Level of Safety – Military
10-8
Low Risk
(acceptable)
Medium Risk
10-6
(should be acceptable)
High Risk
10-4
10-2
(may be acceptable)
Extremely High Risk
(normally unacceptable)
1
Catastrophic
Severity
Negligible
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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
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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
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“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.
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