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decisions when considering alternatives. This section describes the System Safety assessments typically
performed prior to the decision to approve a Mission Need at JRC-1, and prior to the decision to go
forward with the program at JRC-2. The pre-investment safety assessments are: (1) Operational Safety
Assessment (OSA) and (2) Comparative Safety Assessment (CSA).
System Safety Products in the AMS Life Cycle
Hazard Tracking &
Incident Investigat i on
Track Medium and
Hi g h Risks
Closed Loop/Risk Accep tance
Capture & Analyz e
Incidents
Identif y high risk trends
for further detaile d
investigati o n
Operating and Support
Hazard Analysis (O&SHA )
- Operating hazards (focus on
the human errors/factors details
- Support and Maintenance Hazards
System Hazard Analysis
(SHA )
- Looks at interfaces and
environment (operating
and amb ient)
- NAS System Level
Subsystem Hazard Analysis (SSHA)
- NOT components (next level
below System
- Focus on faults and hazards
at SS level
- Detaile d
- A few safety requirements
Comparative Safet y
Assessment (CSA)/Preliminary
Hazard Analysis (PHA )
- Top - down, focus on known
system mission and approaches
and changes at NAS system leve l
- Preliminary in natur e
- Core Safety Requirement s
OSA
- Syste- m Level - Preli-m inary (some
assumptions)
Some- Safety Requirements
INTEGRATED PRODUCT
DEVELOPMENT SYSTEM
may fall out
Figure 4-1: Safety Products in AMS Life Cycle
An Operational Safety Assessment (OSA) has been designed to provide a disciplined, and internationally
developed (RTCA SC189) method of objectively assessing the safety requirements of aerospace systems.
In the FAA, the OSA is used to evaluate Communication, Navigation, Surveillance (CNS) and Air Traffic
Management (ATM) systems. The OSA identifies and provides an assessment of the hazards in a system,
FAA System Safety Handbook, Chapter 4: Pre-Investment Decision Safety Assessments
December 30, 2000
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defines safety requirements, and builds a foundation for follow-on institutional safety analyses related to
Investment Analysis, Solution Implementation, In-Service Management, and Service Life Extension.
The OSA is composed of two fundamental elements: (1) the Operational Services & Environment
Description (OSED), and (2) an Operational Hazard Assessment (OHA). The OSED is a description of
the system physical and functional characteristics, the environment’s physical and functional
characteristics, air traffic services, and operational procedures. This description includes both the ground
and air elements of the system to be analyzed. The OHA is a qualitative safety assessment of the
operational hazards associated with the OSED. Each hazard is classified according to its potential
severity. Each classified hazard is then mapped to a safety objective based on probability of occurrence.
In general, as severity increases, the safety objective is to decrease probability of occurrence.
The information contained in the OSA supports the early definition of system level requirements. It is not
a risk assessment in a classical sense. Instead, the OSA’s function is to determine the system’s
requirements early in the life cycle. The early identification and documentation of these requirements
may improve system integration, lower developmental costs, and increase system performance and
probability of program success. While the OSA itself is not a risk assessment, it does support further
safety risk assessments that are required by FAA Order 8040.4. The follow-on safety assessments may
build on the OSA’s OSED and OHA, by using the hazard list, system descriptions, and severity codes
identified in the OSA. The OSA also provides an essential input into CSA safety assessments that
support trade studies and decision making in the operational and acquisition processes.
The CSA is a safety assessment performed by system safety to assess the hazards and relative risks
associated with alternatives in a change proposal. The alternatives can be design changes, procedure
changes, or program changes. It is useful in trade studies and in decision-making activities where one or
more options are being compared in a system or alternative evaluation. This type of risk assessment can
be used by management to compare and rank risk reduction alternatives. More details on how to perform
a CSA are included in section 4.2.
4.1 Operational Safety Assessment
The OSA is intended to provide system level safety requirements assessment of aerospace CNS/ATM
systems. As described above it is composed of two elements: (1) The Operational Environment Definition
　
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