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basis safety becomes an integral part of the day-to-day business of the organization and that the safetyrelated
activities of the organization are directed to the areas where the benefits will be greatest.
Systems approach
5.1.4 Modern approaches to safety management have been shaped by the concepts introduced in
Chapter 4 and, in particular, by the role of organizational issues as contributory factors in accidents and
incidents. Safety cannot be achieved simply by introducing rules or directives concerning the procedures to
be followed by operational staff.
5.1.5 The scope of safety management encompasses most of the activities of the organization. For
this reason, safety management must start at the senior management level, and the effects on safety must
be examined at all levels of the organization.
5-2 Safety Management Manual (SMM)
System safety
5.1.6 System safety was developed as an engineering discipline for aerospace and missile defence
systems in the 1950s. Its practitioners were safety engineers, not operational specialists. As a result, their
focus tended to be on designing and building fail-safe systems. On the other hand, civil aviation tended to
focus on flight operations, and safety managers often came from the ranks of pilots. In pursuing improved
safety, it became necessary to view aviation safety as more than just the aeroplane and its pilots. Aviation is
a total system that includes everything needed for safe flight operation. The “system” includes the airport, air
traffic control, maintenance, cabin crew, ground operational support, dispatch, etc. Sound safety
management must address all parts of the system.
5.2 FACTORS AFFECTING SYSTEM SAFETY
5.2.1 The factors affecting safety within the defined system can be looked at two ways: first, by
discussing those factors which may result in situations in which safety is compromised; and second, by
examining how an understanding of these factors can be applied to the design of systems in order to reduce
the likelihood of occurrences which may compromise safety.
5.2.2 The search for factors that could compromise safety must include all levels of the organization
responsible for operations and the provision of supporting services. As outlined in Chapter 4, safety starts at
the highest level of the organization.
Active failures and latent conditions
5.2.3 Active failures are generally the result of equipment faults or errors committed by operational
personnel. Latent conditions, however, always have a human element. They may be the result of undetected
design flaws. They may be related to unrecognized consequences of officially approved procedures. There
have also been a number of cases where latent conditions have been the direct result of decisions taken by
the management of the organization. For example, latent conditions exist when the culture of the
organization encourages taking short cuts rather than always following approved procedures. The direct
consequence of a condition associated with taking short cuts would materialize at the operational level by
non-adherence to correct procedures. However, if there is general acceptance of this sort of behaviour
among operational personnel, and management is either unaware of this or takes no action, there is a latent
condition in the system at the management level.
Equipment faults
5.2.4 The likelihood of system failures due to equipment faults is in the domain of reliability
engineering. The probability of system failure is determined by analysing the failure rates of individual
components of the equipment. The causes of the component failures may include electrical, mechanical and
software faults.
5.2.5 A safety analysis is required to consider both the likelihood of failures during normal operations
and the effects of continued unavailability of any one element on other aspects of the system. The analysis
should include the implications of any loss of functionality or redundancy as a result of equipment being
taken out of service for maintenance. It is therefore important that the scope of the analysis and the
definition of the boundaries of the system for purposes of the analysis be sufficiently broad so that all
necessary supporting services and activities are included. As a minimum, a safety analysis should consider
the elements of the SHEL model outlined in Chapter 4.
Chapter 5. Basics of Safety Management 5-3
5.2.6 The techniques for estimating the probability of overall system failure as a result of equipment
faults and for estimating parameters, such as availability and continuity of service, are well established and
are described in standard texts on reliability and safety engineering. These issues will not be addressed
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Safety Management Manual (SMM) 安全管理手册(38)
