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procedures. Listed below are some examples of how safety performance requirements could be stated.
Quantitative requirements. – usually expressed as a failure or accident rate, such as “ the Catastrophic
system accident rate shall not exceed x.xx X 10-Y per operational hour.”
Accident risk requirements – could be expressed as “ No hazards assigned a Catastrophic accident
severity are acceptable.” Accident risk requirements could also be expressed as a level defined by the
accident risk assessment matrix. (see Chapter x. yy) such as “No Category 3 or higher accident risks are
acceptable.”
Standardization requirements – are expressed relative to a known standard that is relevant to the system
being developed. Examples include: The system will comply with the Federal Code of Regulations
CFR-XXX, or “The system will comply with international standards developed by ICAO.”
Safety Design Requirements
The program manager, in concert with the chief engineer and utilizing system engineering and associated
system safety professionals, should establish specific safety design requirements for the overall system.
The objective of safety design requirements is to achieve acceptable accident risk through a systematic
application of design guidance from standards, specifications, regulations, design handbooks, safety
design checklists, and other sources. These are reviewed for safety parameters and acceptance criteria
applicable to the system. Safety design requirements derived from the selected parameters, as well as any
associated acceptance criteria, are included in the system specification. These requirements and criteria
are expanded for inclusion in the associated follow-on or lower level specifications.
A composite list of all SSP requirements is included in the requirements and criteria section of the SSPP
for several reasons. The list includes the following.
Organization and integration of safety requirements establishing clear SSP objectives. Frequently, safety
requirements are included at multiple levels in a variety of specifications. Assembling a safety
requirements composite list can be time consuming and, therefore, generating and formally documenting
this list can expect to save significant staff labor costs and likely omissions by those without significant
system safety experience.
FAA System Safety Handbook, Chapter 5: Post-Investment Decision Safety Activities
December 30, 2000
5 - 15
Providing MA assurance that no safety requirements have been missed and that the safety requirements
have been interpreted correctly.
Documentation
The inclusion of a description of risk assessment procedures, and safety precedence is an important
example of where the SSPP contributes to the MA and the contractor reaching a common understanding.
Without such details explicitly described in the SSPP, both the MA and contractor could, in good faith,
proceed down different paths until they discover the difference of interpretation at a major program
milestone.
The hazard analyses described in Chapters 8 & 9 illustrate some methodologies used to identify risks, and
assign severity and criticality criteria. Safety precedence is a method of controlling specific unacceptable
hazards. A closed loop procedure is required to ensure that identified unacceptable risks are resolved in a
documented disciplined manner. The inclusion of such procedures demonstrates both necessary control
and personnel independence.
The presence of the safety criteria in the SSPP is an important step in the system safety management
process. This information must flow down to the system and design engineers (including appropriate
subcontractors). SSPP must provide a procedure that incorporates system safety requirements and criteria
in all safety critical item (CI) specifications. Such safety requirements include both specific design and
verification elements.
Unambiguous communication between the FAA and the contractor depends on standardized definitions.
The FAA may choose for expediency, to invoke a MIL-STD-882 SSP. It must be noted that the
definitions included in MIL-STD-882 are not identical to those used in the FAA community. Therefore,
the SOW should indicate that the definitions in this handbook (or other FAA documents) supersede those
in MIL-STD-882, see Glossary for examples.
5.3.5 Hazard Analyses
The SSPP describes the specific analyses to be performed during the SSP. The following characteristics
of those analyses should be included.
The analysis techniques and formats to be used in the qualitative or quantitative analysis to identify risks,
their hazards and effects, hazard elimination, or risk reduction requirements, and how these requirements
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System Safety Handbook系统安全手册上(103)
