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available program assets. The system safety activity, like all other systems engineering functions, is sized
through a trade-off between cost, schedule, and performance. The sizing of an SSP must find a balance
between acceptable risk and affordable cost. Neither a system with unacceptable accident risk nor one
that cannot be procured because of the costs of achieving unreasonable safety goals is acceptable.
5.6 Program Interfaces
Both the nature of safety objectives and economics require the use of information available through other
engineering disciplines. The capability of the safety engineering staff can be greatly increased through
integration with other engineering disciplines. System Safety integration and risk assessment have been
discussed in earlier sections of this Chapter. For a summary of other organizations that need to be
involved in system safety, see Table 5-4.
Design engineers are key players in the system safety effort. Together with systems engineers, they
translate user requirements into system design and are required to optimize many conflicting constraints.
In doing this, they eliminate or mitigate known hazards but may create unidentified new hazards. System
safety provides design engineers with safety requirements, validation and verification requirements, and
FAA System Safety Handbook, Chapter 5: Post-Investment Decision Safety Activities
December 30, 2000
5 - 24
advice and knowledge based on the SSP's interfacing with the many participants in the design and
acquisition processes.
On a typical program, safety engineers interface with a number of other disciplines as reflected in Table
5-3. In most cases, the frequency of interfacing with these other disciplines is less than that with the
design engineers. Nevertheless, the exchange of data between safety engineering and the program
functions is both important and in some cases mutually beneficial.
Reliability engineers, for example, perform analyses usable by and often without additional cost to safety
engineering. These analyses do not supplant safety-directed analyses. They provide data that improve
the quality and efficiency of the safety analysis process. Three types of reliability analyses are reliability
models, failure rate predictions, and Failure Modes and Effects Criticality Analysis (FMECA).
The safety/maintainability engineering interface is an example of providing mutual benefits. The system
safety program analyzes critical maintenance tasks and procedures. Hazards are identified, evaluated, and
appropriate controls employed to minimize risk. Maintainability analyses, on the other hand, provide
inputs to the hazard analyses, particularly the Operational and Support Hazard Analyses (O&SHA).
FAA System Safety Handbook, Chapter 5: Post-Investment Decision Safety Activities
December 30, 2000
5 - 25
Table 5-3: Other Engineering Organizations Involved in Safety Programs
ORGANIZATION NORMAL
FUNCTIONS
SAFETY FUNCTIONS
Design
Engineering
Design equipment and
system to meet
contractual
specifications for
mission
Analyses safest designs and procedures. Ensures that safety
requirements in end product item specifications and codes
are met. Incorporates safety requirements for subcontractors
and vendors in specifications and drawings.
Human (Factors)
Engineering
Ensures optimal
integration of human,
machine, and
environment.
Analyses human machine interface for operation,
maintenance, repair, testing, and other proposed tasks to
minimize human error, provide safe operating conditions,
and to prevent fatigue. Makes procedural analysis.
Reliability
Engineering
Ensures equipment will
operate successfully for
specific periods under
stipulated conditions.
Performs failure modes and effects criticality analysis
(FMECA) and failure rate predictions quantifying
probability of failure. Performs tests, as necessary, to
supplement analytical data. Reviews trouble and failure
reports for safety connotations.
Maintainability
Engineering
Ensures hardware status
and availability.
Ensures that operating status can be determined, minimizes
wearout failures through preventative maintenance, and
provides safe maintenance access and procedures.
Participates in analyzing proposed maintenance procedures
and equipment for safety aspects.
Test Engineering Conducts laboratory and
field tests of parts,
subassemblies,
equipment, and systems
to determine whether
their performance meets
contractual requirements.
Evaluates hardware and procedures to determine whether
they are safe in operation, whether additional safeguards are
　
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