Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4897

e) the reports, e.g. of range, will be subject to measurement errors. 6.2.2.2 While any assessment of the effectiveness of ACAS as a whole must take failure to form tracks, item a), into account, there is no need to prove that the logic is effective when it has no data. 6.2.2.3 Late track formation, item b), could delay the generation of RAs (perhaps because the various trackers in the logic have not converged and the RA is delayed by low confidence) or result in an inappropriate initial RA (perhaps because the output of the trackers is used before it has converged). Best practice would be to determine the frequency of late track formation for the actual surveillance system to be used with the logic being tested. 6.2.2.4 Once a track is formed, missing reports can degrade the accuracy of the track or cause low confidence in the track, both of which could delay the initial RA, result in an inappropriate RA or delay changes in an RA after it has been generated. Best practice would be to determine the frequency of missing reports for the actual surveillance system to be used with the logic being tested. The probability that a report is missing on any given cycle will be a function of the range of the intruder, altitude and whether or not a report was missing on the previous cycle. 6.2.2.5 Actual bearing measurement errors are highly dependant on the airframe and the siting of the ACAS antenna and other antennas and obstacles fitted to the same airframe. The bearing measurements are characteristically so poor that early ACAS designs made no use of them in the collision avoidance logic. A later design, which includes a filter that inhibits RAs when the sequence of range measurements indicates a significant horizontal miss distance, used the bearing and bearing rate measurements to verify that neither aircraft is accelerating; the filter is disabled if the bearing measurements are not consistent with the diagnosed miss distance. The conditions specified in Chapter 4, 4.4.2 are intended to cover this sort of feature in the logic. 6.2.2.6 It is most unlikely that any ACAS installation will provide bearing measurements of sufficient accuracy to provide the primary basis of a miss distance filter or any other aspect of the collision avoidance logic. 6.2.2.7 Range and bearing measurements are also used to determine the relative position of the intruder for use in the traffic display. The requirements for this use are much less stringent than those of the collision avoidance logic, and the models specified in Chapter 4, 4.4.2.2 and 4.4.2.3 have no bearing on this use. 6.2.3 ALTITUDE QUANTIZATION 6.2.3.1 The intruder’s altitude could be available as either Mode C or Mode S reports and is thus expressed in 100 ft or 25 ft quanta. Chapter 4, 4.4.2.1 c) specifies that 100 ft quanta be assumed for the purposes of confirming that the performance requirements are met. The performance of the collision avoidance logic is expected to be improved when the intruder’s altitude is available as 25 ft quanta and it is desirable to confirm that this is the case. 6.2.3.2 In most cases, the altitude of own aircraft will be available to ACAS as a measurement prior to the formation of a Mode C or Mode S report and Chapter 4, 4.4.2.1 d) specifies that this is assumed. For installations where it is not possible to provide the original altitude measurement to ACAS, the collision avoidance logic will have to use the Mode C or Mode S reports made by own aircraft. This is expected to degrade the performance of the logic but Chapter 4, 4.4.2.1.1 requires that this degradation be acceptable. The logic is not expected to meet the performance requirement when altitude reports (as opposed to measurements) are used for own aircraft. The test is whether the resulting measures are judged acceptable given that they result from an installation where it has been necessary to compromise performance by using input that does not match the normal standards, and whether they indicate that the logic is unduly sensitive to quantization of the altitude data for own aircraft. 6.2.4 STANDARD ALTIMETRY ERROR MODEL 6.2.4.1 The standard altimetry error model is needed for the calculation of the effect of ACAS on the risk of collision (6.3.2). Although it is based on the observed performance of operational altimeters, there is no intention that the model be used as a reference recording that performance. Still less is there an implied requirement for altimeters to match the performance described in the model whether or not they are used in conjunction with ACAS. The model is standardized solely for the purpose of defining the conditions under which the requirements relating to the performance of the collision avoidance logic apply. 6.2.4.2 The model describes the distribution that is to be assumed for the errors in altimeter measurements. It excludes the effect of the quantization that is needed to create Mode C or Mode S altitude reports. Nevertheless, the calculation of the effect of ACAS on the risk of collision must take full account of this quantization and this is to be achieved by quantizing the simulated altitude measurements and thus forming simulated reports that are provided to the simulated ACAS logic. 6.2.4.3 The simulations of the effect of ACAS will include precise knowledge of the aircrafts’ measured altitudes. Their actual altitudes are not known either to ATC or to the aircraft; they are the sum of the simulated measurement and the random altimeter error. In every encounter where the horizontal miss distance is very small, there is some risk of collision and it equals the probability that the difference in the actual altitudes of the two aircraft is small enough for them to collide. Thus the calculation of the effect of ACAS on the risk 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 ATT-52 of collision (6.3.2) involves forming the statistical distribution of the error in the measured difference in the altitudes of the two aircraft: the convolution of two statistical distributions, one for each aircraft. 6.2.4.4 For the standard altimetry error model specified in Chapter 4, 4.4.2.4, the probability that the actual vertical separation d is less than a threshold value h (which is taken to be 100 ft in 6.3.2) is as follows: for λ1 = λ2 and a ≥h Prob(|d| ≤ h) = for λ1 = λ2 and a < h Prob(|d| ≤ h) = for λ1 ≠λ2 and a > h Prob(|d| ≤ h) = and for λ1 ≠λ2 and a < h Prob(|d| ≤ h) = where λ1 and λ2 are the values of λ for the two aircraft, and a is the apparent vertical separation as in 6.3.2, i.e. the altitude separation as measured by the altimeters in the two aircraft. 6.2.5 STANDARD PILOT MODEL 6.2.5.1 The standard pilot model represents a reasonable expectation of pilots’ normal reaction to RAs. However, it does not capture the full range of potential responses, for example, slow responses that undermine collision avoidance and excessively violent reactions that cause large deviations from clearance. For some responses, for example, failure to respond or a decision to move to the next flight level in response to a climb RA, it is not appropriate to examine the performance of the logic, but the following modifications to the standard model will provide an indication whether the logic is unduly dependent on an accurate pilot response. 6.2.5.2 In the context of Chapter 4, 4.4.3, the reduction in the risk of collision, a suggested deficient pilot response is:

Source: https://magyarkozlony.hu/hivatalos-lapok/7e70cec03f34e3c2efd8610b865b65591eafd701/dokumentumok/a55dc160549d57fa4db0035e37c6a6a98dd1a0b9/letoltes