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depicted in Figure 1.3.2A are used.
FAA System Safety Handbook, Appendix F
December 30, 2000
F-36
Figure 1.3.2A Key Fault Tree Analysis Symbols
The output event. Identification of a particular event in the sequence of an operation.
A basic event.
.
An event, usually a malfunction, for which further causes are not normally sought.
A normal event. An event in an operational sequence that is within expected performance standards
.
An “AND” gate. Requires all of the below connected events to occur before the above connected event can o. ccur
An “OR” gate. Any one of the events can independently cause the event placed above the OR gate
.
An undeveloped event. This is an event not developed because of lack of information or the event lacks significance.
Transfer symbols. These symbols transfer the user to another part of the diagram. These symbols are used to
eliminate the need to repeat identical analyses that have been completed in connection with another part
of the fault tree.
RESOURCES: The System Safety Office is the best source of information regarding Fault Tree
Analysis. Like the other advanced tools, the FTA will involve the consultation of a safety professional or
engineer trained in the use of the tool. If the probabilistic aspects are added, it will also require a database
capable of supplying the detailed data needed.
COMMENTS: The FTA is one of the few hazard identification procedures that will support
quantification when the necessary data resources are available.
EXAMPLE: A brief example of the FTA is provided at Figure 1.3.2B. It illustrates how an event may be
traced to specific causes that can be very precisely identified at the lowest levels.
FAA System Safety Handbook, Appendix F
December 30, 2000
F-37
Figure 1.3.2B Example of Fault Tree Analysis
Fire Occurs in
Storeroom
Combustibles
stored in
storeroom
Ignition source
In storeroom
Stock Material
Degrades to
Combustible State
Electrical Spark
Occurs
Direct Thermal
Energy Present
Radiant Thermal
Energy Raises
Combustibles
Leak into
Storeroom
Combustibles
Stored in
Storeroom
Airflow
< Critical
Valve
And
Or
Or
1.3.3 THE FAILURE MODES AND EFFECTS ANALYSIS
FORMAL NAME: The Failure Modes and Effects Analysis
ALTERNATIVE NAMES: The FMEA
PURPOSE: The Failure Modes and Effects Analysis (FMEA) is designed to evaluate the impact due to
the failure of various system components. A brief example of FMEA illustrating this purpose is the
analysis of the impact of the failure of the communications component (radio, landline, computer, etc.) of
a system on the overall operation. The focus of the FMEA is on how such a failure could occur (failure
mode) and the impact of such a failure (effects).
APPLICATION: The FMEA is generally regarded as a reliability tool but most operational personnel
can use the tool effectively. The FMEA can be thought of as a more detailed “What If” analysis. It is
especially useful in contingency planning, where it is used to evaluate the impact of various possible
failures (contingencies). The FMEA can be used in place of the "What If" analysis when greater detail is
needed or it can be used to examine the impact of hazards developed using the "What If" tool in much
greater detail.
FAA System Safety Handbook, Appendix F
December 30, 2000
F-38
METHOD: The FMEA uses a worksheet similar to the one illustrated at Figure 1.3.3A. As noted on the
sample worksheet, a specific component of the system to be analyzed is identified. Several components
can be analyzed. For example, a rotating part might freeze up, explode, breakup, slow down, or even
reverse direction. Each of these failure modes may have differing impacts on connected components and
the overall system. The worksheet calls for an assessment of the probability of each identified failure
mode.
Figure 1.3.3A Sample Failure Mode sand Effects Analysis Worksheet
FAILURE MODES AND EFFECTS ANALYSIS
Page ___of ___Pages
System_________________________ Date_______________
Subsystem _____________________ Analyst_____________
Component
Description
Failure
Mode
Effects on
Other Components
Effects
On
System
RAC or
Hazard
Category
Failure Frequency
Effects
Probability
Remarks
RESOURCES: The best source of more detailed information on the FMEA is the System Safety Office.
EXAMPLES: An example of the FMEA is provided at Figure 1.3.3B.
Figure 1.3.3B Example FMEA
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