Publication: Magyar Közlöny
Issue: MK-2009-104 (Year: 2009, Number: 104)
Era: 2004-2010
Section: 
Paragraph Index: 2491

b) it assumes aircraft are approaching on an ILS glide path. In that case, 610 m (2 000 ft) AGL corresponds to a distance of approximately 11.2 km (6 NM) from an airport. New approach procedures (e.g. based on MLS or GNSS) may require additional considerations to limit interference. And even with ILS approach, it is recommended to establish procedures switching ACAS II and ACAS III to “stand-by” while the aircraft is not on an active runway. 3.2.3.4 Inequality (2) ensures that the transponder on board the ACAS aircraft will not be turned off by mutual suppression signals from the ACAS unit on the same aircraft more than 1 per cent of the time. 3.2.3.5 Inequality (3) ensures that a “victim” Mode A/C transponder will not generate more than 40 Mode A/C replies in a one-second period in response to interrogations from all the ACAS interrogators within its detection range. Like inequality (1) it includes terms to account for reduced transmit power, to account for the other ACAS interrogators in the vicinity, and to limit the power of a single ACAS unit. Forty Mode A/C replies per second is approximately 20 per cent of the reply rate for a transponder operating without ACAS in a busy area of multiple Mode A/C ground sensor coverage. 3.2.3.6 EXAMPLE OF INTERFERENCE LIMITING 3.2.3.6.1 As an example, when interrogation limiting is not invoked, the overall Mode A/C and Mode S interrogation rates of a directional ACAS unit would typically be as follows: the Mode A/C interrogation rate kt is typically constant at 83 whisper-shout interrogations per second. Assume that the sum of the normalized whisper-shout powers, i.e. the Mode A/C contribution to the left-hand side of inequality (1), is approximately 3. The Mode S interrogation rate depends on the number of Mode S aircraft in the vicinity. In en-route airspace it is typically an average of about 0.08 interrogations per second for each Mode S aircraft within 56 km (30 NM). In a uniform aircraft density of 0.006 aircraft per square km (0.02 aircraft per square NM), the number of aircraft within 56 km (30 NM) is 57. If 20 per cent of these are ACAS equipped, na = 12 and the variable term on the right-hand side of inequality (1) is 21.5. If the number of ACAS aircraft in the area does not exceed 26, the fixed term continues to govern and no limiting occurs until there are approximately 100 Mode S aircraft within 56 km (30 NM). Attachment Annex 10 — Aeronautical Communications ATT-19 22/11/07 3.2.3.6.2 Similar considerations hold for inequalities (2) and (3). In inequality (2) the mutual suppression interval associated with each top antenna interrogation is 70 microseconds. The bottom antenna mutual suppression interval is 90 microseconds. Thus the Mode A/C contribution to the left-hand side of inequality (2) is 0.0059 and the Mode S interrogation rate can be as high as 59 top antenna interrogations per second before violating the limit. With a typical whisper-shout sequence, the left-hand side of inequality (3) is approximately 3. The number of ACAS aircraft within 56 km (30 NM) can be as high as 26 without violating inequality (3). 3.2.3.6.3 When the interrogation rate or density increases to the point at which one of the limits is violated, either the Mode A/C or Mode S normalized interrogation rate or both must be reduced to satisfy the inequality. If the density were to reach 0.029 aircraft per km2 (0.1 aircraft per NM2) uniformly out to 56 km (30 NM), there would be 283 aircraft within a 56 km (30 NM) radius. If 10 per cent of these were equipped with ACAS, na = 28. The right-hand limits in inequalities (1) and (3) would then be 9.66 and 2.76 respectively. To satisfy these lower limits, the Mode A/C and Mode S contributions to the left-hand side of inequality (1) would both have to be reduced. As a result, the surveillance range of both Mode A/C and Mode S targets would be less. 3.2.3.6.4 Inequality (1) contains an exponent α which serves to match the inequalities to the specific local ACAS aircraft density such that a “victim” transponder operating in the vicinity of ACAS that are distributed within the limits of uniform-in-area to uniform-in-range will never detect more than 280 ACAS interrogations in a one-second period. The value of α defines the local ACAS distribution characteristic within the vicinity of own ACAS. It is based on the relative numbers of ACAS within 56 km (30 NM), within 11.2 km (6 NM) and within 5.6 km (3 NM) as derived from ACAS broadcast interrogations and from ACAS surveillance. The value of α is the minimum of:

Source: https://magyarkozlony.hu/hivatalos-lapok/1f7c6b0e16b4b71a92e5ad24416008bbe2e26aab/dokumentumok/710811d1f7f958a2990684d0cbf918e84f5497e5/letoltes