Rigorous analytical technique, called criticality determination methodology /or CD technique/ determines the probability that a given complex system will successfully achieve stated objectives. The CD technique identifies critical elements of the system by a failure mode and effects analysis

Cox, C. T.

Eagle, K. H.

Malik, D. F.

Wolin, S.

English

NASA Technical Reports Server

July 1968	 Brief 68-10252 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
New Method for Critical Failure Prediction of Complex Systems 
A rigorous analytical technique, called "criticality 
determination methodology" (or CD technique) has 
been developed for determining the probability that 
a given complex system will successfully achieve 
stated objectives. The CD technique identifies critical 
elements of the system (e.g., a Saturn V Launch 
Vehicle/Apollo mission) by a failure mode and effects 
analysis. A critical element is defined as one whose 
failure (critical failure) may result in one or more 
objective losses. 
As an illustration, in order to determine the con-
tribution of the Saturn V Launch Vehicle to the 
possible loss of the Apollo Mission, a numerical pre-
diction quantity (criticality number) is generated by 
criticality analysis techniques. Each stage, system, 
subsystem, and component is analyzed to determine 
its contribution to the loss of mission, vehicle, crew, 
or other critical objective. Critical components are 
identified, and a criticality number is calculated for 
each component. The component criticality numbers 
are then combined in determining subsystem, system, 
stage, and vehicle criticality numbers. The criticality 
number is defined as the expected number of objec-
tive losses (vehicle, mission, or crew) in a million 
preflight or flight attempts (as applicable) attributable 
to failure of a given component in a specific mode and 
environmental condition during a given period of op-
eration. Criticality numbers can be assigned to com-
ponents, subsystems, stages, vehicles, missions, and 
crews for any given failure distribution. 
The CD technique has been employed successfully 
in making reliability determinations of the Saturn V 
vehicle by analyzing all the critical components in 
their critical modes for single failure points of all the 
stages and systems for prelaunch and flight opera-
tions. A single failure point (critical) is defined as a
single component whose failure by itself may result 
in an objective loss. 
By means of the CD technique the probability of 
an objective loss is determined by multiplying the 
probability of a specific failure, the failure mode pro-
portion, and the probability of an objective loss 
should the given failure occur. 
The CD technique has been completely automated 
for the Saturn V Launch Vehicle/Apollo mission. 
Raw data is fed directly into the computer, which 
automatically performs all data reduction and calcu-
lations and produces final report printouts. The tech-
nique integrates the results of many separate analyses 
which were not combined or even compatible in pre-
vious techniques. Some examples of such separate 
analyses pertain to failure mode and effects, critical-
ity, reliability, safety, flight trajectory, systems opera-
tions research, and time line. 
Notes: 
1. The CD technique should be particularly applica-
ble to urban planning, air and water pollution 
problems, and to oceanology. 
2. Complete details may be obtained from: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B68-10252 
Patent status: 
No patent action is contemplated by NASA. 
Source: K. H. Eagle, C. T. Cox, 
D. F. Malik, and S. Wolin 
of The Boeing Company 
under contract to 
Marshall Space Flight Center 
(MFS-14133) 
Category 02 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
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New method for critical failure prediction of complex systems

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