Availability |
The
probability that a system will be able to perform its designated function
when required for use. |
Equipment Elements |
The Site
& Building Infrastructure, Building Plant, ATS Operational Equipment, Human
Interface, External Services and Facilities elements of a system. |
Error |
A
discrepancy between a computed, observed or measured value or condition and
the true, specified or theoretically correct value or condition. An error is
that part of a system state that is liable to lead to a failure. A failure
occurs because there is an error in the system. |
Failure |
Termination of the ability of a system or component to perform a required
function. |
Functional Failure Mode |
A way a
function can fail. Functional Failure Modes are used in the derivation of
safety requirements. Functional failure modes appropriate to most systems
include Loss, Corruption, Delay and Misdirection. |
Maintainability |
The
ability of an item under given conditions to be retained in, or restored to,
a state in which it can perform the required function more effectively. |
People Elements |
The ATS
Personnel, both Engineering and ATC together with relevant training and
development functions in their role as elements of a system. |
Procedure Elements |
The
Airspace sectorisation, Engineering maintenance and ATC procedural elements
of a system. |
Random Error |
An error
that is introduced at random into the system. For example, errors caused by
component failure or violation of maintenance instructions. |
Random Failure |
A
failure that appears at random. This may be due to random error, or to a
combination of systematic error and random exposure of the error. This
includes pseudo-random errors, which are entirely deterministic but for
which the combination of circumstances. |
Reliability |
The
probability that during a certain period of time a system will perform the
functions described in the requirements under the stated conditions. |
Risk |
The
probability of occurrence, together with the severity of the consequences,
of a hazardous event. |
Safety |
Freedom
from unacceptable risk. |
Safety Assessment |
The
undertaking of an investigation, in order to arrive at a judgment, based on
evidence, of the functional safety achieved by a system. |
Safety Case |
A
documented account of the evidence, arguments and assumptions to show that
system hazards have been identified and controlled, both in engineering and
operational areas, and that qualitative and quantitative safety requirements
have been met. |
Safety Plan |
Documentation of a safety programme that is planned, integrated and
developed in conjunction with other design, development, production and
quality control activities. |
Safety Related Software |
Software
that implements functions, the failure of which may comprise a hazard. |
Safety Related System |
A system
which:
* Implements functions necessary to achieve or maintain a safe state; and
* Is intended to achieve, on its own or with other safety related systems
or external risk reduction facilities, the level of safety integrity
necessary for the implementation of the required functions |
Software |
Programs, procedures, data rules and associated documentation pertaining to
the operation of a computer system. |
System |
A
combination of physical components, procedures and human resources organised
to achieve a function. Systems encompass a number of elements including:
*Site and building infrastructure;
*
Building
plant;
*ATS
operational equipment;
*
Human
interface;
*
Airspace
sectorisation and ATS procedures;
*
ATS
personnel;
*
Training
and development functions;
*
External
services and facilities. |
Systematic Error |
An error
that is always present in a given version of a system. For example, software
design errors or maintenance procedure errors. |
Systematic Failure |
A
failure that is not a random failure. |
Validation |
Confirmation by examination and provision of objective evidence that the
requirements have been fulfilled. Validation is generally used to refer to a
larger process than verification (see below). In particular, whereas
verification tests against specifications, validation is concerned with
whether the operation of the system provides the results needed by the
users. Validation therefore includes the consideration of whether the
specification of a system sufficiently and accurately represents the needs
of the intended user. |
Verification |
Confirmation by examination and provision of objective evidence that the
requirements have been fulfilled. Verification is generally used to refer to
the process of determining whether the product of each phase of the
development process is consistent with the requirements specified in a
previous phase. |