Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4902

c) the pilot fails to respond to weakening RAs. 6.2.5.4 The logic is not expected to meet the performance requirements when the pilot responds as described above, but calculation of the performance measures using these nonstandard pilot responses will provide some insight into the sensitivity of the logic to the accuracy of the pilot’s response. The test is whether the changes in the measures are judged acceptable given that they result from an inaccurate response, and whether they indicate that the logic is unduly sensitive to the response assumed from the pilot. 6.2.6 STANDARD ENCOUNTER MODEL 6.2.6.1 Effectively, there are two encounter models, one for use in risk ratio calculations (where the horizontal miss distance is small) and the other for use when assessing the compatibility of the logic design with ATM (where the horizontal miss distance can be comparable with the ATC horizontal separation minimum). This overcomes what would otherwise be an unacceptable simplification: both models treat the horizontal and vertical characteristics of the encounters independently. 6.2.6.2 The standard model is the result of an analysis of a large amount of ground radar data collected in two States. This means that one can expect the performance measures calculated using this standard model to be related to operational reality even though that is not the purpose of the calculations. The data analysed revealed very considerable variation in the airspace characteristics expressed in the 4λ ------ a h + ( ) – λ -------------------     2h λ -----    2λ a h – + ( ) 2λ a h + + ( ) – exp exp 4λ ------ a h + ( ) – λ --------------------     2a λ -----    2λ a – h + ( ) 2λ a h + + ( ) + exp exp – λ2 a – λ1 -----     h λ1 ----     λ2 a – λ2 -----     h λ2 ----     sinh exp – sinh exp λ1 λ2 – -------------------------------------------------------------------------------------------------------- λ2 1 1 h – λ1 -----     h a λ1 -----     cos exp – λ2 2 1 h – λ2 -----     h a λ2 ----     cos exp – – λ1 λ2 – ----------------------------------------------------------------------------------------------------------------------------------- 2007/70/II. szám Attachment Annex 10 — Aeronautical Telecommunications ATT-53 28/11/02 encounter model depending on the location of the radar providing the data. The characteristics of the data from the two States were radically different. This implies that a standard encounter model cannot provide predictions of performance that will be valid for any specific location. However, given that a standard model is essential to the definition of standard performance, the model standardized is considered sufficiently complex and representative. 6.2.6.3 To determine the parameters of the standard encounter model (Chapter 4, 4.4.2.6), for example the relative weights of the encounter classes, encounters were reconstructed from ground radar data. This required a reinterpretation of aspects of the encounters, examples of which are given below. 6.2.6.3.1 The definition of “Altitude layer” given for the standard encounter model (Chapter 4, 4.4.1) is simple because it is made solely for the purpose of standardizing the collision avoidance logic. When, in the real encounters observed in the ground radar data, ground level did not correspond to a pressure altitude of 0 ft, it was necessary to distinguish between height above the ground and pressure altitude with respect to mean sea level (MSL). The method used to determine the altitude layer appropriate for an encounter observed in real radar data was to place it in Layer 1 if it occurred less than 2 300 ft above ground level (AGL), and to use the pressure altitude with respect to MSL otherwise. At locations of high altitude, one or more layers were sometimes missing. 6.2.6.3.2 The vertical rates of an aircraft at the beginning and the end of an encounter, and are, in the standard encounter model, values at precise times, viz. tca – 35 s and tca + 5 s. When processing the data for real encounters observed in the ground radar data, the values used for and were the average vertical rates over the first 10 s, i.e. [tca – 40 s, tca – 30 s], and the last 10 s, i.e. [tca, tca + 10 s], of the encounter. 6.2.6.3.3 In similar vein, in the real encounters tca was the actual time of closest approach, and hmd was the actual horizontal separation at closest approach. The vertical miss distance, vmd, was either the vertical separation at closest approach, for encounters in which hmd ≥ 500 ft, or it was the minimum vertical separation during the period of time in which the horizontal separation of the two aircraft was less than 500 ft. 6.2.6.3.4 Some aspects of the standard encounter model, e.g. the magnitude of speed changes during an encounter, could not be determined from examination of the ground radar data (because of the nature of the data) and had to be specified using a general understanding of aircraft dynamics. 6.2.6.3.5 To put the lack of precise correspondence between the model encounters and those observed in radar data into context, it is necessary to bear in mind that the purpose of the standard encounter model is to provide a basis for standardizing the performance of the collision avoidance logic. While, naturally, every realistic effort was made to ensure that the model is as faithful as possible to operational reality, precise fidelity is not required and will not have been achieved. This is not a reason for using an alternative model; the only model that is valid for assessing the performance of the collision avoidance logic against the requirements stated here is the model specified here for that purpose. 6.2.6.4 Any construction of the standard encounter model that can be proved equivalent to that specified in Chapter 4, 4.4.2.6 is acceptable. Two examples of such equivalent alternatives are given below. 6.2.6.4.1 Chapter 4, 4.4.2.6.1 specifies that the performance measures be calculated by creating sets of encounters defined by broad characteristics (specifically: the ordering of the aircraft addresses; the altitude layer; the encounter class; and the approximate value for the vertical miss distance) and combining the results from these sets by using the weights specified in Chapter 4, 4.4.2.6.2. This will involve as many simulations of relatively rare types of encounters, e.g. crossing encounters, as of the more common types of encounters, e.g. non-crossing encounters. This approach ensures that the full range of possibilities within each set is properly investigated. However, the same end can be achieved by creating a number of encounters for each set that is proportional to the specified weight and combining all the encounters into one much larger pool. The only caveat on this alternative approach is that the total number of encounters must be large enough to ensure that the results from the smallest set, considered in isolation, are statistically reliable. 6.2.6.4.2 The statistical distributions for each of the vertical rates have been specified by requiring that first an interval is selected within which the final value is to lie, and then the final value is selected using a distribution that is uniform within the interval. This is merely a device adopted for the sake of clear presentation of the tables in Chapter 4, 4.4.2.6.3.2.4. It would be equivalent to select the value directly using a statistical distribution that is linear within each of the intervals and for which the cumulative probability increases across each interval by an amount equal to the specified probability for that interval. 6.2.6.5 The encounters in the standard encounter model are constructed from a notional closest approach outwards. The time of this notional closest approach is fixed and written “tca” in Chapter 4, 4.4.2.6. In the vertical plane, the vertical rates 35 s before tca and 5 s after tca are selected and joined by a period of acceleration if necessary, and then the altitudes in the trajectory are fixed by requiring that the vertical separation at tca equals the selected value for “vmd”. In the horizontal plane, selected values for “hmd”, the approach angle, and the aircraft speeds define the relative trajectories of z· z· z· z· 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 ATT-54 the two aircraft at the time tca. The aircraft turns and speed changes are then imposed by modifying the trajectories before and after tca. At the conclusion of this process, the time of closest approach only approximates tca. 6.2.7 ACAS EQUIPAGE OF THE INTRUDER 6.2.7.1 The standards specify three sets of conditions concerning the equipage of the intruder and the way the intruder aircraft is to be assumed to behave:

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