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information acquired through the assessments.
13.2 THE SAFETY ASSESSMENT PROCESS
13.2.1 Chapter 6 introduced the two-dimensional concept of risk: the perceived risk associated with a
hazardous event depends on both the likelihood of occurrence of the event, and the severity of its
consequences. The safety assessment process addresses both these factors. Safety assessments are a
particular application of the risk management process, building upon the systematic processes of risk
management described in Chapter 6. The safety assessment process can be divided into seven steps as
outlined in Table 13-1.
13.2.2 Figure 13-1 illustrates the safety assessment process diagrammatically, and shows the
possible need to perform a number of cycles of the process until a satisfactory method of risk mitigation is
found.
Table 13-1. Seven steps for safety assessment
Step 1: Development (or procurement) of a complete description of the system to be
evaluated and of the environment in which the system is to be operated;
Step 2: Identification of hazards;
Step 3: Estimation of the severity of the consequences of a hazard occurring;
Step 4: Estimation of the likelihood of a hazard occurring;
Step 5: Evaluation of risk;
Step 6: Mitigation of risk; and
Step 7: Development of safety assessment documentation.
Chapter 13. Safety Assessments 13-3
Figure 13-1. The safety assessment process
Describe the system
to be assessed
Describe the
operational
environment
Identify hazards
Identify
consequences
Make estimate
of risk
Is risk
acceptable?
No
Yes
Identify risk
mitigation measures
Make new
estimate of risk
Yes Is risk
acceptable?
No
Is risk ALARP? No
Yes
Yes
No
Document decision
and proceed to next
stage of development
or implementation
Abandon project
or revise original
project objectives
Is risk tolerable?
13-4 Safety Management Manual (SMM)
13.2.3 Not surprisingly, the safety assessment process closely parallels the risk management process
described in Chapter 6. The remainder of this chapter will examine each of the seven steps of a safety
assessment in more detail.
STEP 1: DEVELOPMENT OF A COMPLETE DESCRIPTION OF THE SYSTEM TO BE EVALUATED
AND OF THE ENVIRONMENT IN WHICH THE SYSTEM IS TO BE OPERATED
The “system”, as defined for the purpose of safety assessment, will always be a sub-component of some
larger system. For example, even if the assessment encompasses all services provided within an
aerodrome, this can be considered a sub-component of a larger regional system, which in turn is a subcomponent
of the global aviation system.
If all potential hazards are to be identified, the persons involved in the safety assessment must have a good
understanding of the proposed new system or change, and how it will interface with the other components of
the overall system, of which it is a part. This is why the first step in the safety assessment process is to
prepare a description of the proposed system or change.
The hazard identification process can only identify hazards that come within the scope of the system
description. The boundaries of the system must therefore be sufficiently wide to encompass all possible
impacts that the system could have. In particular, it is important that the description include the interfaces
with the larger system, of which the system being assessed is a part.
A detailed description of the system should include:
a) the purpose of the system;
b) how the system will be used;
c) the system’s functions;
d) the system’s boundaries and the external interfaces; and
e) the environment in which the system will operate.
The safety impact of a potential loss or degradation of the system will be determined, in part, by the
characteristics of the operational environment in which the system will be integrated. The description of the
environment should therefore include any factors that could have a significant effect on safety. These factors
will vary from one case to another. They could include, for example, traffic characteristics, airport
infrastructure and weather-related factors.
The description of the system should also address contingency procedures and other non-normal
operations, for example, failure of communications or navigation aids.
For large-scale projects, the system description should address the strategy for transition from the old to the
new system. For example, will the existing system be de-commissioned and replaced immediately with the
new system, or will the two be operated in parallel for a period of time?
　
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