| | Title | Definition |
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| System Safety Working Group | A formally charted group of persons representing organisations associated with the system under study, organised to assist management in achieving the system safety objectives. |
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| Systematic failure | Failures due to flaws in design, manufacture. Items subjected to the same conditions fail consistently. Dealt with by means of integrity levels. |
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| Systematic Failures | A failure caused by errors in the specification, design, construction operation or maintenance which cause the item to fail under some particular combination of inputs or conditions. All software failures are systematic failures. |
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| Systems Approach | A step - by - step procedure for solving problems; a decision making process which moves from the general to the specific; an iterative process. |
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| Systems Engineering | The orderly process of bringing a system into being . A "system" comprises a complex combination of resources (in the form of human being, materials, equipment, software, facilities, data, information, ervices, etc), integrated in such a manner as to fullfill a designated need.
The application of scientific and engineering effort to: (1) transfor an operational need intoa sescription of system performance paramaters and a system configuration thorugh the use of an interative process of definition, synthesis, analysis, design , test and evaluation, and validation; (2) integrate related technical paramaters and ensure tha compatibility of all physical, fucntional , and programme interfaces in a manner that optimises the total definition and design; and (3) integrate relaibility, maintainability, useability (human facotrs), safety, producibility, supportability (serviceability), disposability,, and other such facotrs into a total engineering effort to meet cost, schedule, and technical performance objectives. [Blanchard, BS, System Engineering Management] |
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| Tailplane | Horizontal aerofoil member of an aeroplane's tail assembly or empennage. Provides longitudinal stability in flight. Known as the stabilizer in US aviation parlance (see also elevators). |
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| Technical Airworthiness | Is a concept, the application of which defines the condition of an aircraft, and supplies the basis for judgement of the suitability for flight of that aircraft in that it has been designed, constructed, operated and maintained to approved standards by competent individuals, who are acting as members of an authorised organisation and whose work is both certified as correct and accepted on behalf of the regulatory authority. |
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| Threat | A state of the system or system environment which can lead to adverse effect in one or more given risk dimensions. [ISO/IEC 15026, 3.21] |
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| Threshold | The point at which a runway begins. |
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| Transponder | Radio device fitted to aircraft which, when triggered off by certain radar wavelengths, emits a signal visible on ground radar screens. Signal usually includes additional information such as altitude of the aircraft. |
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| Trim | Adjusting control of aircraft in climb, level flight and descent, so pilot is not required to maintain continuous pressure on elevators, ailerons or rudder. |
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| T-VASIS | T Visual Approach Slope Indicator System. |
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| Type Certificate | The Type Certificate is considered to include the type design, the operating limitations, the type certificate data sheet, the applicable requirements with which the Authority records compliance, and any other conditions or limitations prescribed for the product in the appropriate Regulatory Code [JAR21.4]. |
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| UHF (Ultra High (radio) Frequency) | Frequency band of 300 to 3000 MHZ. Aviation use confined mainly to military aircraft. |
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| Uncommanded | This term is used to consider the consequences of a system/equipment failure resulting in the "unintended and undemanded" operation [AMC to CS25.1309]. |