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时间:2011-08-28 14:57来源:蓝天飞行翻译 作者:航空
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5.1 Safety assessment
The primary function of air traffic control is to provide safe separation between aircraft. This is achieved by implementing minimum horizontal and vertical separations, which must not be simultaneously reduced.
The probability of collision, or loss of separation, between two aircraft is generally attributable to human (aircrew or controller) error. There is a risk of collision, between any pair of aircraft, in every encounter that requires controller intervention and the application of radar separation between those aircraft. However radar separation standards are only applied in the horizontal plane and the minima can only be applied when each aircraft is under positive radar control.
5.1.1 Collision risk
The collision risk is the probability of a mid-air accident in a prescribed volume of airspace for a specified number of flight hours due to loss of planned separation and where one collision is considered to produce two accidents (RGCSP - 1A-5).
Factors contributing to the risk of collision include:
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the circumstances requiring the provision of radar separation,

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airspace structure,

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sector capacity,

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communications system occupancy,

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air traffic controller workload,

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pilot/aircrew workload,

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the actual horizontal distance between aircraft,

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both aircraft being at, or passing through, the same level,

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system function,

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the radar plot position error (volume of uncertainty of the aircraft’s position) indicating a correct separation where it is actually negligible.


All potential causes of collision must be identified and, where possible, analysed. To determine the appropriate radar separation minima the analysis is related to the effect of inaccuracies, in the displayed radar data, so as to estimate the risk of collision and to decide whether the risk, for the implementation of a particular radar separation minimum within the radar coverage of a specific radar system, is acceptably safe.
The ICAO Review of the General Concept of Separation Panel (RGCSP) has recommended a TLS of 5x10 -9 fatal accidents per flight hour per dimension (lateral, longitudinal and vertical) arising from collisions due to any cause for systems planned for implementation after the year 2000 (RGCSP - WG/A --5/95). This TLS applies to the risk of collision due to all causes, i.e. technical performance, human error etc.
There is no ICAO RGCSP recommendation as to what proportion of the TLS should apply to the risk of collision, within a radar environment, due to the inaccurate radar data. Previous work (See Attachment B) has arbitrarily used a proportioning factor of 10% of 5x10-9. This results in a TLS due to inaccurate radar data, of 5x10-10 fatal accidents per flight hour. This TLS does not apply to other causes of collision risk such as lack of accuracy or timeliness in the radar display.
5.1.2 Collision risk due to radar system inaccuracy
It is possible that errors in the accuracy of the radar data, presented to the controller by the RDP system, may be sufficient to cause loss of separation, or worse. The risk of collision, attributable to the system function, depends upon the:
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accuracy, integrity and availability of the ATC radar system,

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accuracy, integrity and availability of the communications system (A/G-G/G),

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contingency support to the radar and Communications systems, and

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established ATC procedures.


5.2 Technical assessment
This section does not aim for a full description of the intricate relation between radar separation and radar system performance. However it is felt that a common understanding of the technical aspects will contribute consistently to the objectives of the whole document.
 
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