Avionics News March 2018 - 67

The Inman Risk Matrix Chart

Order 8040.4B gives specific
definitions to the severity row.
Catastrophic is defined as having
multiple fatalities (or fatality to all on
board), usually with the loss of the
aircraft and/or vehicle. Hazardous is
defined as multiple serious injuries; a
fatal injury to a relatively small number
of persons (one or two); or a hull loss
without fatalities. Major is defined as
physical distress or injuries to persons
or substantial damage to the aircraft or
vehicle. Minor is defined as physical
discomfort to persons or slight damage
to the aircraft or vehicle. Perhaps
the funny bone incident could be
considered minor. Minimal is defined
as having a negligible safety effect.
Each cell in the table gets a letter and a number. To someone
analyzing an event, the need for action becomes quite clear.
For example, an event rating 5A happens frequently and
causes multiple lives to be lost. Someone should take action
immediately in this case. At the other end of the spectrum, an
extremely improbable event, which poses negligible risk is rated
1E. Someone would have trouble justifying an expenditure of
time or funds to address a 1E event.
The table also is color coded, with red indicating high risk,
and immediate action should be taken. 5A through C, 4A, 4B,
and 3A are all colored red. Even the remote possibility of a
catastrophic event should be addressed immediately. According
to 8040.4B, "This safety risk requires mitigation, tracking and
monitoring."
The yellow areas of the table indicate medium risk. According
to 8040.4B, "This safety risk is acceptable without additional
mitigation; however, tracking and monitoring are required. It is
desirable to achieve the lowest practicable risk levels (factoring
in the principles of appropriate resource management), thus
mitigation of medium risk is recommended but not required."
The green cells indicate low risk. According to 8049.4B,
"This safety risk is acceptable without restriction or limitation;
hazards are not required to be actively managed, but they must
be documented and reported if a safety risk assessment has been
performed."
Students can be simultaneously skeptical and curious. To
them, the chart seems somewhat arbitrary. We did a little more
research. You can, too. If you are curious about risk assessment
charts, I recommend conducting a Google image search of "Risk
Assessment Matrix." Hundreds will show up. Some have the
most severe on the right, and most are color coded. Some have
numbers. Some have an additional row to indicate a risk has
been eliminated. The charts with numbers allow the reader to get
an idea of the logic behind the recommendations for action. For
all the tables, high probability or frequent catastrophic events
require action, and of course, we don't need a table to tell us that.

At the other end of the spectrum, an extremely rare occurrence,
no more severe than a funny bone bump, is obviously not a
candidate for immediate action, or any action at all. It's the areas
in the middle that become subjects for debate.
In these areas, the charts may differ, depending on how they
were developed. In his paper titled Risk Analysis for the Subsea
Template Installation in Arctic, Eugene Pribytkov used a matrix
similar to the FAA matrix. Pribytkov used a risk matrix he
found on a website called, Best Template & Design Images. The
most significant difference between the FAA table and the table
used by Pribytkov is the use of numbers and multiplication to
determine action. In this matrix, severity also is given numbers,
1 through 5. Multiplying likelihood and severity gives a product,
which can be used to determine action. In the chart he used, any
product above 15 was considered an unacceptable risk.
For experimental purposes, we equated unacceptable risk with
that requiring immediate action, then applied the numbers to the
FAA table. When compared to the Pribytkov model, we found our
industry has a slightly lower threshold for unacceptable situations
requiring immediate action. The FAA chart also has a lower
threshold for consideration of action, with remotely occurring
events causing negligible injury or damage considered for action.
As an additional experimental numeric hazard assessment
chart, I assigned 0 to negligible severity, 1 to minor, and went
with odd numbers up to 7 for catastrophic. For probability, I
assigned extremely improbable a value of negative 6, and then
used odd numbers up to 7 for frequent. Then I simply added
the numbers. Numbers 10 or greater match the International
Civil Aviation Organization table for high risk. Numbers 3 or
greater but less than 10 also match the ICAO table for medium.
Numbers less than 4 match the ICAO table for low risk.
After examining charts and doing math, even my most
skeptical students see the value of a hazard assessment matrix.
The curious among them get a deeper understanding of the
process of risk assessment. My hope is that after they graduate
and take a job, they gain a reputation for being safer than the
average technician. q
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Table of Contents for the Digital Edition of Avionics News March 2018

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