Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4800

b) an established Mode C track or a Mode C track in the process of being acquired traverses into that beam from another beam. ACAS switches back to the single interrogation after ten surveillance update intervals in which two correlating acquisition replies were not received. 3.2.3 INTERFERENCE LIMITING 3.2.3.1 ACAS equipment conforms to a set of three specific inequalities (Chapter 4, 4.3.2.2.2.2) for controlling interference effects. The three inequalities, applicable to ACAS operating below a pressure altitude of 5 490 m (18 000 ft), are associated with the following physical mechanisms: (1) reduction in “on” time of other transponders caused by ACAS interrogations, (2) reduction in “on” time of own transponder caused by mutual suppression during transmission of interrogations, and (3) Mode A/C fruit caused by ACAS Mode A/C interrogations. Setting na to 1 in inequalities (1) and (3) for ACAS operating above pressure altitude of 5 490 m (18 000 ft), prevents a single ACAS from transmitting unlimited power by providing an upper limit on the ACAS one-second interrogation power/rate product. 3.2.3.2 Inequality (1) ensures that a “victim” transponder will never detect more than 280 ACAS interrogations in a one-second period from all the ACAS interrogators within 56 km (30 NM) for any ACAS distribution, surrounding the “victim” transponder, within the limits of uniform-in-range to uniform-in-area. The left-hand side of the inequality allows an ACAS unit to increase its interrogation rate if it transmits at less than 250 W since low power transmissions are detected by fewer transponders. Each normalized power value within the summation in the left-hand side of this inequality contains an exponent α which serves to match the inequality to the localized ACAS distribution. The value of α defines the local ACAS aircraft distribution curve and is derived from own ACAS measurement of the distribution and number of other ACAS within 56 km (30 NM) range. As the ACAS distribution varies from uniform-in-area (α = 1) to uniform-in-range (α = 0.5), the density, and therefore the electromagnetic impact, of ACAS aircraft in the vicinity of a “victim” transponder becomes greater. This increased potential for ACAS interference is offset by the greater degree of interference limiting that results from using an exponent of less than one in the normalized power values of the inequality. The denominator of the first term on the right-hand side of this inequality accounts for other ACAS interrogators in the vicinity and the fact that all ACAS units must limit their interrogation rate and power in a similar manner so that, as the number of ACAS units in a region increases, the interrogation rate and power from each of them decreases and the total ACAS interrogation rate for any transponder remains less than 280 per second. 3.2.3.3 Within an airspace in which ACAS aircraft are distributed between the limits of uniform-in-range to uniform-in-area, and provided that the “victim” is taken off the air for 35 microseconds by suppression or reply dead time whenever it receives an ACAS interrogation, the total “off” time caused by ACAS interrogations will then never exceed 1 per cent. Measurements and simulations indicate that the total “off” time can be higher than 1 per cent in high-density terminal areas because of ACAS aircraft distributions that are beyond the region defined by uniform-in-area to uniform-in-range and because of a Mode S transponder recovery time to certain interrogations that is expected to be greater than 35 microseconds. The second term on the right-hand side of this inequality limits the maximum value of the interrogation power-rate product for ACAS II, regardless of na, in order to allow a portion of the total interference limiting allocation to be used by ACAS I. The term, which is matched to the ACAS distribution by the value of α in the denominator, ensures that an individual ACAS II unit never transmits more average power than it would if there were approximately 26 other ACAS II nearby distributed uniformly-in-area or approximately 6 other ACAS II nearby distributed nearly uniformly-in-range. 3.2.3.3.1 High-density terminal areas will suffer from higher loads due to violation of the 1 per cent estimate at approximately 14.8 – 18.5 km (8 – 10 NM) from touch down. To ensure sufficient surveillance performance for both ACAS and ground surveillance systems in such areas, ACAS flying below 610 m (2 000 ft) AGL include also ACAS II and ACAS III operating on ground in the calculation of nb and nc. This value was chosen for practical reasons:

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