Glossary of Terms

	Title	Definition
	Safety Critical	A term applied to a condition, event, operation, process or item which is essential to safe system operation or use (e.g. Safety Critical Function, Safety Critical Path, Safety Critical Item, etc) All interactions, elements, components, subsystems, functions, processes, interfaces, within the system that can affect a predetermined level of risk.
	Safety Critical Computer Software Module	Those computer software modules whose errors can result in a hazardous or catastrophic or critical severity
	Safety Critical Item	An item whose failures can cause hazards of catastrophic or critical severity.
	Safety Critical Item	Any item whose failures can case hazards of catastrophic or critical severity.
	Safety Incident	Any unplanned event or series of events, other than an actual accident, which had the potential to cause death, injury, or occupational illness to people; or otherwise cause damage to the environment.
	Safety Integrity Level (SIL)	The likelihood of a safety related system satisfactorily performing the required safety functions under all the stated conditions within a stated period of time. An indication of the required level of protection against failure (degree to which a component must be free from flaws).
	Safety Involved Item	An item whose failures can only cause hazards of catastrophic or critical severity in combination with external (independent) failures.
	Safety Management	The application of engineering and management principles and techniques in order to optimise all aspects of safety within constraints of operational effectiveness, time and cost. It is a systematic and explicit approach to managing safety. A methodology that drives safety as a measurable design parameter (ensuring that an acceptable level of safety is designed into the product) and provides a form of measure of that achievement.
	Safety Management System	A 'Safety Management System' is an explicit element of the corporate management responsibility which sets out a company's safety policy and defines how it intends to manage safety as an integral part of its overall business. The SMS is a management tool for executing safety throughout the life cycle of a project.
	Safety monitoring	Safety monitoring, as related to digital systems, is a means of protecting against specific failure conditions by directly monitoring a function for failures that could contribute to the failure condition. Monitoring functions may be implemented in hardware, software, or a combination of both. Through the use of monitoring techniques, the software level of the monitored function may be reduced to the level associated with the loss of its related function. To allow this level reduction, there are four important attributes of the monitor that should be determined: Software level. Safety monitoring software is assigned the software level associated with the most severe failure condition category for the monitored function. System fault coverage. Assessment of the system fault coverage of a monitor ensures that the monitor's design and implementation are such that the faults which it is intended to detect will be detected under all necessary conditions. Independence of Function and Monitor. The monitor and protective mechanism are not rendered inoperative by the same functional failure condition that causes the hazard. Hardware integrity. The monitor hardware integrity will need to be commensurate with the hazard. A configuration which requires high integrity monitor software but proposes low integrity monitor hardware would be unacceptable.
	SAR	Search and Rescue.
	SEC	Spoiler/Elevator Computer.
	Severity	An expression of consequence used in the assessment a specific hazard.
	Severity Category	Qualitative description of Worst Case credible consequences of hazard.
	SFCC	Slat/Flap Control Computer.

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