default logo
TC 56

IEC TC 56

Dependability

FAQs

How is Dependability related to performance?

Dependability manages performance threats such as errors, mistakes, faults and failures. It can be applied to a simple device or to a complex system of systems. It can commence at the conceptual stage for a design comprised of components or a design based upon pre-manufactured units and also at any stage of the life cycle. It can be applied to services, manufacturing processes or to data transfers.

Wherever there is a performance requirement there will be threats and dependability is available to manage these threats. Dependability provides trust, and confidence that a system will perform as required.

Dependability is qualitative and can usually only provide comparative measures. Quantitative measures, however, are derived from its attributes; the prime ones being availability, reliability, maintainability and maintenance together with supportability and support. In some cases, durability, recoverability, integrity and security attributes are included within the scope of dependability. Although safety is usually not within the scope of dependability there is a major overlap as threats to safety are likely to be threats to performance.

The use of quantitative measures assumes that the performance of an item is defined under a set of given conditions, these can be environmental levels and stress levels (internal and external) that occur during the useful life states and their durations. Usually these are defined within a useful life profile.

Current systems can be highly flexible, permitting changes such as enhancements, extensions and changes in its useable boundaries. These may affect one or more measures; however, the dependability processes are sufficiently robust to enable these measures to be re-assessed to ascertain the suitability of the system for its revised purpose/requirement. In these instances, sustainability and dependability become closely aligned.

Management of dependability ensures that an efficient, effective and economical approach is always adopted.

Detailed information on dependability management can be found in IEC 60300-1.

How is Availability related to performance?

Availability is concerned with the state to perform with respect to all possible life states of a system. Usually, the boundary defining which useful life states are included or excluded will determine the measurement required.

Availability provides the “balance” between reliability and maintainability plus supportability. Improving availability can be achieved by improving reliability or by improving maintainability/supportability. By considering all influences including cost and risk, the preferred option can be selected thereby balancing these attributes to derive the required availability.

How is Reliability related to performance?

Reliability is the ability of a system to perform as required, without failure, for a given interval (time, operating cycles, distance etc.). One of the activities of reliability is to ascertain if an error/fault/failure is actually a threat to the required performance.

Performance threats are then managed as follows:

  • prevent the threat – initiating changes to the design to remove possible failures;
  • tolerate the threat – avoiding system failure although faults have occurred. For example, by the introduction of redundancy;
  • mitigate the threat – the threat occurs, but the impact of the threat is reduced by initiating design changes or introducing safety gates.

How is Maintainability and maintenance related to performance?

Maintainability is the ability of a system to be retained in or restored to a state to perform. Maintenance is the combination of all technical and management actions intended to retain an item in, or restore it to, a state in which it can perform.

Performance threats are managed as follows:

  • prevent the threat – recognising that a fault is likely to occur, scheduled maintenance durations are established where items can be serviced or replaced before the potential fault can result in system failure. In some cases, the schedule occurs without affecting operation;
  • tolerate the threat – initiating system design changes to enable items to be restored whilst the system continues to operate;
  • mitigate the threat – the threat occurs and the system becomes non-operational. Failed systems are restored to an operational state as quickly as possible.

How is Supportability and support related to performance?

Supportability and support are the “glue” that enables maintenance to function. Without the organisational skills, capable resources, calibrated equipment, tools, spare parts, consumables and facilities, maintenance would not be able to function. Where any of the above are not available to implement the maintenance actions then a Logistic Delay Time is incurred.

What Standards are prepared by TC 56?

Click here to see list of standards prepared and maintained by TC 56.

Why TC 56 standards are important?

TC 56 Dependability standards set the framework for establishing Dependability management systems in an organization, whether it is a large corporation or a small business enterprise. TC 56 standards provide guidelines for dependability management to maximize the benefits of applying timely dependability disciplines and best practices in product development and in service provision to meet competitive global market demands.

TC 56 standards complement ISO 9000 series of Quality standards to deal specifically with the time-dependent issues that are critical in achieving business/project success. These are performance issues are related to the delivery of dependable products and customer satisfaction. They are influenced by contributing factors in reliability, maintainability, and maintenance support. The challenge of dependability as reflected in many of the TC 56 standards is to help optimize investment planning, source selection, and effective project implementation to minimize business risk exposures. This leads to reduce long-term ownership costs by judicious application of life cycle processes.

Dependability standards are used in business contracts. They provide common understanding of terminology to facilitate international trade. Dependability standards provide assessment methods and practical measures to ensure the successful outcome of product dependability and quality of service.

Dependability standards are non-prescriptive. They are used as guidance on application of proven dependability techniques and tools during the various product life cycle phases for continual improvement.

How do TC 56 standards apply to my project?

Dependability projects generally deal with product performance to meet user needs and strive to satisfy the customers. A product has its life cycle phases: from concept and definition, through design and development, manufacturing, installation, operation and maintenance, to its final discontinued use and disposal. The project of interest may involve any phase or phases of the product life cycle. TC 56 standards are organized for ease of identification and implementation by grouping the relevant standards in a simple hierarchy. Such arrangement is reflected in the TC 56 standard structure to facilitate user information access. Guidance in standard selection and application is provided in IEC 60300-1.

TC 56 standards structure

TC 56 standards are divided into 3 categories:

  • Core standard – standard providing overview on dependability fundamentals, objectives or management.
  • Process standard – standard giving guidance on a particular dependability issue related to an aspect of management or to a life cycle phase.
  • Support standard – standard giving technical information of general relevance in various dependability issues.
  • Associated standard – standard in which TC56 has contributed, but is not directly responsible for its development.

Click here to see list of standards prepared and maintained by TC 56.

How are TC 56 standards developed?

TC 56 standards are developed by consensus with contributions from participating National Committee (NC) experts on the subject. A New Proposal (NP) is prepared and circulated to seek NC support when the subject of standardization is considered important to industry. A Working Draft is normally submitted along with the NP to provide sufficient information to justify initiation of the standard work. Upon approval by the NC in voting on the NP, the TC 56 Secretary will assign a project number to a responsible Working Group or a dedicated Project Team to initiate the work. The standard development process takes about 3 to 5 years from NP, through Committee Draft (CD) and Committee Draft in Voting (CDV) to reach its Final Draft International Standard (FDIS) stage before its publication as an International Standard (IS) bearing a unique IEC number.

How are TC 56 standards maintained to keep up-to-date?

TC 56 standards are maintained to keep up-to-date by means of a maintenance process. It takes into account the anticipated future needs of industry to ensure that TC 56 standards meet those needs. The Maintenance Teams are established in each of the TC 56 Working Groups and have experts nominated by the National Committees assigned to review and revise the standard for maintenance purposes. A process for voting confirmation or withdrawal is put in place for the standard going through the maintenance process. Each candidate standard is subject to a maintenance review within a 5-year period.

Are TC 56 standards used for compliance purposes?

TC 56 standards are non-prescriptive. They are not intended for compliance purposes. However, TC 56 standards may be referenced in business contracts for their technical guidance and recommended methods.