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13 -
19
Table 13-2: Software Safety Activities Relative to the Software Life Cycle
Life Cycle Phase Corresponding
Safety Activity
Inputs Expected Results Milestones To
Be Met
Concept/
Requirements/
Specifications
-Review software concept for
safety provisions
-Derive generic and systemspecific
software safety
requirements.
-Analyze software requirements
for hazards.
-Identify potential software/system
interface hazards
-Develop Functional Hazards List
(FHL)
-Develop initial Preliminary
Software Hazard Analysis (PSHA)
-Preliminary
Hazard Analysis
(PHA) [from
system safety
analysis]
-Generic and
system-wide
safety specs.
PSHA Report
PHL
Software
Concept Review
(SCR)
Software
Requirements
Review (SRR)
and Software
Specification
Review (SSR)
Architecture/
Preliminary
Software Design
At high design level:
-Identify Safety Critical Computer
Software Components (SCCSCs)
-Verify correctness &
completeness of architecture
-Ensure test coverage of software
safety requirements.
PSHA Software Safety
Architectural Design
Hazard Analysis
(SSADHA) Report
Preliminary
Design Review
(PDR)
Detailed Design
At the low design(unit) level:
-Focus on SCCSCs at the unit
level.
-Verify correctness/ completeness
of detail. Design
PSHA
SSADHA
Software Safety Detailed
Design Hazard Analysis
(SSDDHA) Report
Critical Design
Review (CDR)
Implementation
Coding
-Examine correctness &
completeness of code from safety
requirements.
-Identify possibly unsafe code.
-Walk-through/audit the code
PSHA,
SSADHA,
SSDDHA
Software Safety
Implementation Hazard
Analysis (SSIHA) report
Test Readiness
Review (TRR)
Integration and
Testing
-Ensure test coverage of software
safety requirements.
-Review test documents and results
for safety requirements.
-Final SSHA
Test documents -Software Safety
Integration Testing
(SSIT) Report
-Final SSHA report
Acceptance
Operations and
Maintenance
-Operating and Support Hazard
Analysis (O&SHA)
All of the above
plus all incidents
reports
O&SHA Report(s), as
required
Deployment
FAA System Safety Handbook, Chapter 13: Launch Safety
December 30, 2000
13 -
20
Figure 3 provides a composite overview of the entire safety process. The figure consists of three parts.
The top part reflects the broader System Safety Process described in draft Advisory Circular 431.35-2.
The middle part illustrates a typical waterfall Software Acquisition Process life cycle. The bottom part
also partly corresponds to the Systematic Software Safety Process. In Figure 3, all processes shown in
horizontal bars are subject to a hypothetical schedule with time duration not drawn to any scale.
Phase-independent software safety activities
NASA’s Software Safety Standard 8719.13A mentions activities not tied to specific phases. The Standard
lists the following ones meant to occur throughout the life cycle:
· Tracing safety requirements keeping track of the software safety requirements during design,
coding and testing, including the correspondence between these requirements and the system
hazard information.
· Tracking discrepancies between the safety and development aspects of the software.
· Tracking changes made to the software to see if they impact the safety process.
· Conducting safety program reviews to verify if safety controls are being implemented to
minimize hazards.
Special Provisions
Commercial Off the Shelf (COTS): COTS software targets a broad range of applications, with no
specific one envisioned ahead of time. Therefore, care must be taken to ensure COTS software presence
minimizes risk when it becomes embedded or coupled to specific applications. Consideration ought to be
given to designing the system such that COTS software remains isolated from safety-critical functions. If
isolation is not possible, then safeguards and oversight should be applied.
Software Reuse: Reusable software originates from a previous or different application. Usually,
developers intend to apply it to their current system, integrating it “as is” or with some minor
modifications. The Software Safety Team verification/validation plan, etc.) Annex B should serve as a
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