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Critical Systems

A critical system is any system whose failure could result in threats to human life or the existence of an organization, significant economic losses and/or environmental harm. Since so many of these systems are increasingly computer-based, managing these risks requires specialized software and hardware engineering.

Key Characteristics


The ability of the system to deliver services conforming to specification. Concerned with the number of times a service fails to deliver specified services.


How likely the system is available to deliver services when requested. Especially important for real-time systems and “non-stop systems” which must run continously.


The capacity of the system to evolve or adapt to new requirements. Also considers the ease of repairing the system after a failure has been discovered.


The ability of the system to operate without catastrophic failure, i.e. to deliver its services in such a way that human life or the system’s environment will not be damaged.


How the system protects itelf against accidental or deliberate damage. Affects other attributes as a security failure can compromise reliability, availability and safety.

Eighty-five to ninety percent of our nation's critical information systems are owned by the private sector. It is therefore crucial that utilities organizations and IT vendors work together to close gaps in the security of this infrastructure.

Tom Noonan, former chairman, president and chief executive officer of Internet Security Systems, Inc


Integration of “off-the-shelf” components

Off-the-shelf systems are not designed with criticality in mind, yet their low cost and other advantages make them critical to business operations. Therefore, devising a way to safely incorporate them in critical systems becomes a crucial business requirement.

Operations Design

As automated systems become more complex, there is an increasing chance of operational errors.  Designing systems that either avoid this or become proportionally more resilient is an absolute necessity but non-trivial.

Achieving rapid delivery of critical systems

Organisational requirements are constantly increasing for rapid system development, but critical systems development is tipically lengthy. It is imperative to reconciliate these two distinct realities through formal and professional systems engineering.

Reliability Models

Fail-operational systems

Continue to operate when their control systems fail. Examples of these include elevators, the gas thermostats in most home furnaces, and passively safe nuclear reactors.

Fault-tolerant systems

Avoid service failure when faults are introduced to the system.  The normal method to tolerate faults is to have several computers continually test the parts of a system, and switch on hot spares for failing subsystems

Fail-secure systems

Maintain maximum security when they can not operate. For example, while fail-safe electronic doors unlock during power failures, fail-secure ones will lock, keeping an area secure.

Fail-Passive systems

Continue to operate in the event of a system failure. An example includes an aircraft autopilot.

Fail-safe systems

Become safe when they cannot operate. Many medical systems fall into this category.

Yearly cost of IT failures worldwide (in USD)
Collective downtime across all website outages in 2014

Typical cost of downtime per hour by Industry
(in millions of USD)







[Sources: Vision Solutions, Assessing the Financial Impact of Downtime]

Typical cost of downtime per hour by Industry
(in millions of USD)







[Sources: Vision Solutions, Assessing the Financial Impact of Downtime]


Aerospace and Defense

Higher performance, increased capability, improved reliability and uncompromised safety are among the key  factors that drive technical advances in aerospace and defence. Integrating software and safety engineering processes for the development of air traffic control software, providing guidance  for safety assurance of command and control systems, developing safety requirements for UAVs, and evaluating safety aspects of communication systems on airborne platforms are some examples of critical system engineering.

Medical Technology

Software intensive systems are an increasingly vital part of health care delivery both with respect to the management and distribution of patient data and the life critical real-time operation of complex medical devices.  Standards such as ISO 14971 guide medical device companies in addressing the challenge of balancing residual risks with the anticipated benefits of using an innovative technology to treat patients.


The wellbeing and security of all societies depends on the availability of critical infrastructure, such as the electric grid, water supply infrastructure, oil and gas facilities and public warning systems, which are often managed using critical systems such as Integrated Control Systems (ICS) or other similar types of control systems. These critical systems are undergoing modernization to improve safety, security and reliability.  Modernization efforts also aim to increase efficiency by means of automation and remote  operation.


Cost Reduction

When compared to the disastrous financial impact that systems failure can produce, guaranteeing that critical systems can avoid or tolerate failure is a smart investment.


Critical systems can be adapted to a customer’s specific business agility needs to better achieve its advantages.

Availability Increase

Using advanced critical system engineering know-how and mission-critical support, military-grade availability can be achieved on production systems.

impact cost reduction
more flexible
availability increase



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