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Technique (PERT).2 It is essentially the presentation of system safety tasks, events and activities on a
network in sequential and dependency format showing independencies, and task duration and completion
time estimates. Critical paths are easily identifiable. Its advantage is the greater control provided over
complex development and production programs as well as the capacity for distilling large amounts of
scheduling data in brief, orderly fashion. Management decisions are implemented. Needed actions may be
more clearly seen, such s steps to conduct a specific test.
A similar or sub-technique of PERT is known as Critical Path Method (CPM).3 It also involves the
identification of all needed steps from a decision to a desired conclusion --depicted systematically –to
determine the most time-consuming path through a network. This is designated on the diagram as the
“critical path”. The steps along the path are “critical activities”.
Because of the dynamics and the variability of safety management efforts, the networks developed should
suit the complexity required. For large programs a master PERT network can be developed with lower
level PERT charts referenced to provide needed detail. The use of CPM, in conjunction with PERT, can
explore possible variables that influence programs.4 Further detail on PERT and CPM can be acquired
from the references.
5.4.6 Integrated System Safety Requirements
The integrated engineering requirements for system safety are described within the ISSPP. As the design
and analysis matures specific system safety standards and system specifications are to be developed and
the ISSPP is to be updated. Initially, generic requirements are defined for the design, implementation, and
application of system safety within the specific project, or process. The Integrator defines the
requirements needed to accomplish the objectives of the ISSPP. Here one specifies the system safety
products to be produced, the risk assessment code matrix, risk acceptability criteria, and residual risk
acceptance procedures. This effort should also include guidelines for establishing project phases, review
points, and levels of review and approval.5
5.4.7 Integrated Risk/Hazard Tracking and Risk Resolution
Integrated Risk/Hazard Tracking and Risk Resolution is described within the ISSPP. This is a procedure
to document and track contributory system risks and their associated controls by providing an audit trail
of risk resolution. The controls are to be formally verified and validated and the associated contributory
2 J.V. Grimaldi and R.H. Simonds, Safety Management, Richard D. Irwin, Inc. Homewood, Illinois, Third Edition, 1975.
3 IBID, Grimaldi
4 System Safety Society, System Safety Analysis Handbook, 2nd Edition, 1997.
5 J. Stephenson, System Safety 2000, A Practical Guide for Planning, Managing, and Conducting System Safety Programs, Van
Nostrand Reinhold, New York, 1991.
FAA System Safety Handbook, Chapter 5: Post-Investment Decision Safety Activities
December 30, 2000
5 - 21
Figure 5-4: Safety Verification Methods
hazard is to be closed. This activity is conducted and/or reviewed during ISSWG meetings or formal
safety reviews.
Integrated Risk/Hazard Tracking and Risk Resolution is accomplished by the use of the Safety Action
Record (SAR). The SAR document captures the appropriate elements of hazard analysis, risk assessment
and related studies, conducted in support of system safety. See Chapter 2 for a discussion of the Hazard
Tracking/Risk Resolution process ( Paragraph 2.2.1.5)
5.4.8 Integrated Safety Verification and Validation
Specific verification techniques are discussed within the ISSPP. Safety verification is needed to assure
that system safety is adequately demonstrated and that all identified system risks that have not been
eliminated are controlled. Risk controls (mitigation) must be formally verified as being implemented.
Safety verification is accomplished by the methods shown in Figure 5-4.
It should be noted that no single method of verification indicated above provides total system safety
assurance. Safety verification is conducted in support of the closed-loop hazard tracking and risk
resolution process.
Hazard Control Analysis considers the possibility of insufficient control of the system. Controls are to be
evaluated for effectiveness. They are to enhance the design. Keep in mind that system safety efforts are
Vibration
Thermal
Acoustic
Modal Survey
EMC
Environmental
Functional
Performance
Test
Analysis
Demonstration
Similarity
Inspection
Validation of records
Simulation
Review of design documentation
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System Safety Handbook系统安全手册上(107)
