Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4796

b) Any further attempts consist of a single interrogation during the entire six update intervals. 3.1.3.8.4 When a valid acquisition reply is received, the VS field in the reply is examined to determine the vertical status of a target. If a target is determined to be on the ground, its vertical status is periodically monitored by interrogating as often as necessary to ensure timely acquisition when airborne. When a valid acquisition reply is received from an airborne target, one or more interrogations are to be transmitted to the target within two surveillance update intervals in order to confirm the reliability of the altitude data and the altitude quantization bit. When two replies have been received from an airborne target that have altitude values within 150 m (500 ft) 2007/70/II. szám Attachment Annex 10 — Aeronautical Telecommunications ATT-11 28/11/02 of each other and within 3 050 m (10 000 ft) of own altitude and have identical quantization bit values, periodic surveillance interrogations (designated as “tracking” interrogations) are to be initiated for that target. 3.1.3.8.5 The range of the target is used with its estimated range rate to determine its potential threat to ACAS. If the target is not an immediate potential threat, it can be interrogated less frequently than if it were a potential threat for which an advisory would soon most likely be issued. Each 1-second surveillance update interval, the potential threat level (TAU) of the target is calculated as follows: TAU = – (r – SMOD2/r)/ , where r is the tracked range, is the estimated relative range rate and SMOD is a surveillance distance modifier which is equivalent to 5.6 km (3 NM). If the estimated relative range rate is either a negative value of less than –6 kt or positive (either a slow convergence or the aircraft are diverging), the value used to calculate TAU is –6 kt. An SMOD value of 5.6 km ensures that ACAS will always use the nominal 1-second interrogation cycle in situations where the value of TAU can change rapidly, such as in a parallel approach. A target with a TAU value of equal to or less than 60 seconds is interrogated at the nominal rate of once every second. A target with a TAU value greater than 60 seconds is interrogated at a rate of once every five seconds if the altitude of the target and own aircraft are both less than 5 490 m (18 000 ft) and at a rate of at least once every five seconds if the altitude of the target or own aircraft is greater than 5 490 m (18 000 ft). 3.1.3.9 MODE S SURVEILLANCE EXTENSION 3.1.3.9.1 The equipment passes position reports for a Mode S target to the collision avoidance algorithms only if all replies used for threat assessment after the initial range acquisition occur within range and altitude windows centred on range and altitude predicted from previous reply history, the altitude quantization bit matches the previous value, and the VS field in the short special surveillance reply indicates the target to be airborne at least once during the previous three surveillance update cycles. The range and altitude windows are the same as those used for Mode A/C tracking in 3.1.2.9.2 and 3.1.2.9.3 respectively. 3.1.3.9.2 If a tracking interrogation fails to elicit a valid reply, additional interrogations are transmitted. The total number of tracking interrogations addressed to a single target is not expected to exceed five during a single surveillance update period or sixteen distributed over six successive surveillance update periods. The first tracking interrogation is transmitted using the antenna that was used in the last successful interrogation of that target. If two successive tracking interrogations fail to elicit valid replies from a target, the next two interrogations to that target are transmitted using the other antenna. 3.1.3.10 Missing Mode S replies. The equipment continues to pass to the collision avoidance algorithms predicted position reports for Mode S targets for six surveillance update intervals following the receipt of the last valid reply to a tracking interrogation if the target is interrogated once every second or for eleven 1-second surveillance update intervals following receipt of the last valid reply to a tracking interrogation if the target is interrogated once every five seconds. The equipment does not pass position reports for Mode S targets for more than six surveillance update intervals following the receipt of the last reply to a tracking interrogation whose rate is once every second or for more than eleven 1-second surveillance update intervals following receipt of the last reply to a tracking interrogation whose rate is once every five seconds unless the target again satisfies the range acquisition criteria of 3.1.3.7. The Mode S address of a dropped track is retained for four additional seconds to shorten the reacquisition process if squitters are received. 3.1.3.11 Mode S overload. The equipment passes position reports for all Mode S targets regardless of the distribution of targets in range, provided the total peak target count does not exceed 30. 3.1.3.12 Mode S power programming. The transmit power level of Mode S tracking interrogations to targets (but not airto-air coordination interrogations) is to be automatically reduced as a function of range for targets within 18.5 km (10 NM) as follows: PT = Pmax + 20 log , where PT is the adjusted power level, Pmax is the nominal power level (typically 250 W), which is transmitted to targets at ranges of 18.5 km (10 NM) or more, and r is the predicted range of the target. The actual transmitted power is the lesser of PT and the limit imposed by the interference limiting inequalities of Chapter 4, 4.3.2.2.2.2. 3.1.3.13 Mode S track capacity. When the aircraft density is nominally 0.087 Mode S aircraft per km2 (0.3 aircraft per NM2) in the vicinity of the ACAS aircraft, there will be about 24 aircraft within 9.3 km (5 NM) and about 142 aircraft within 56 km (30 NM) of the ACAS aircraft. Thus, the ACAS equipment is expected to have capacity for at least 150 aircraft addresses. 3.1.3.14 USE OF BEARING ESTIMATES FOR 3.1.3.14 MODE S SURVEILLANCE 3.1.3.14.1 Bearing estimation capability is not required for high-density Mode S surveillance. However, if bearing estimates are available, it is seen that the use of directional Mode S interrogations significantly reduces the transmitter power requirement of the equipment. Directional Mode S interrogations may also be used in the absence of bearing information, provided the interference limits are not exceeded. r· r· r· r ----- 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 ATT-12 3.1.3.14.2 Bearing estimates may also be used in conjunction with knowledge of own airspeed to reduce the overall Mode S interrogation rate. The following is one possible way of achieving such a reduction. 3.1.3.14.3 Instead of calculating time-to-endanger based on the conservative assumption that the two aircraft are on a head-on collision course, the time-to-endanger can be increased by taking into account the threat bearing and the limited turn-rate of own aircraft and allowing for the time that would be required for own aircraft to turn in the direction of the threat. Such computation would continue to assume that the target aircraft is travelling at its reported maximum capable speed directly toward the collision point. 3.2 Transmitter 3.2.1 POWER LEVELS 3.2.1.1 In the absence of interference and when using an antenna whose pattern is identical to that of a quarter-wave monopole above a ground plane, it is possible to provide reliable air-to-air surveillance of transponders at ranges of 26 km (14 NM) by using a nominal effective radiated power of 54 dBm (250 W). 3.2.1.2 The transmitter output power is to be carefully limited between transmissions because any leakage may severely affect the performance of the Mode S transponder on board the ACAS aircraft. The leakage power into the transponder at 1 030 MHz is generally to be kept at a level below –90 dBm. If the physical separation between the transponder antenna and the ACAS antenna is no less than 50 cm, the coupling loss between the two antennas will exceed 20 dB. Thus, if the RF power at 1 030 MHz at the ACAS antenna terminal does not exceed –70 dBm in the inactive state, and if a minimum antenna spacing of 50 cm is adhered to, the direct interference from the ACAS antenna to the transponder antenna will not exceed –90 dBm. This requirement is to ensure that, when not transmitting an interrogation, ACAS does not radiate RF energy that could interfere with, or reduce the sensitivity of, the SSR transponder or other radio equipment in nearby aircraft or ground facilities. 3.2.1.3 Measures must also be taken to ensure that direct 1 030 MHz leakage from the ACAS enclosure to the transponder enclosure is below –110 dBm when the two units are mounted side-by-side in a typical aircraft installation. 3.2.1.4 It is expected that the ACAS equipment be tested side-by-side with Mode S transponders of equivalent classification to ensure that each unit meets its sensitivity requirements in the presence of transmitter leakage from the other. 3.2.2 CONTROL OF SYNCHRONOUS INTERFERENCE BY WHISPER-SHOUT 3.2.2.1 To control Mode A/C synchronous interference and facilitate ACAS operation in airspace with higher traffic densities, a sequence of interrogations at different power levels may be transmitted during each surveillance update period. Each of the interrogations in the sequence, other than the one at lowest power, is preceded by a suppression pulse (designated S1) 2 microseconds preceding the P1 pulse. The combination of S1 and P1 serves as a suppression transmission. S1 is transmitted at a power level lower than that of P1. The minimum time between successive interrogations is to be 1 millisecond. All interrogations in the sequence should be transmitted within a single surveillance update interval. 3.2.2.2 Because the suppression transmission in each step is always at a lower power level than the following interrogation, this technique is referred to as whisper-shout. The intended mechanism is that each aircraft replies to only one or two of the interrogations in a sequence. A typical population of Mode A/C transponders at any given range may have a large spread in effective sensitivity due to variation in receivers, cable losses, and antenna shielding. Ideally, each transponder in the population will respond to two interrogations in the sequence, and will be turned off by the higher power suppression transmissions accompanying higherpower interrogations in the sequence. Given a situation in which several aircraft are near enough to each other in range for their replies to synchronously interfere, it is unlikely they would all reply to the same interrogation and, as a result, the severity of synchronous interference is reduced. Use of whisper-shout also reduces the severity of the effects of multipath on the interrogation link. 3.2.2.3 Figure A-2a defines a whisper-shout sequence that is matched to the requirements for high-density Mode A/C surveillance and Figure A-2b defines a whisper-shout sequence that is matched to the requirements for low-density Mode A/C surveillance. Five distinct subsequences are defined; one for each of the four beams of the top-mounted antenna and one for the bottom-mounted omnidirectional antenna. The interrogations may be transmitted in any order. When the high density sequence of Figure A-2a is truncated to limit interference, the steps are dropped in the order shown in the column Interference limiting priority. When the low-density sequence of Figure A-2b is reduced in power to limit interference, each interrogation and its related MTL value, as indicated in the last column, is reduced by 1 dB in the order shown in the column Interference limiting priority. The lowest numbered steps in the sequence are dropped or reduced first. The timing of individual pulses or steps in either sequence is defined in Figure A-3 which illustrates the three lowest-power steps in the top-forward antenna sequence. The first pulse of the interrogation serves as the second pulse of the suppression. 3.2.2.4 The minimum triggering level (MTL) values tabulated in Figure A-2a and Figure A-2b are based on the assumption that replies to all interrogations are received 2007/70/II. szám Attachment Annex 10 — Aeronautical Telecommunications ATT-13 28/11/02 Figure A-2a. Example of high-density whisper-shout sequence FORWARD DIRECTION S S S S S I I I I I I TOP ANTENNA EFFECTIVE RADIATED POWER (dBm) NOTES.— “I” indicates ERP of P , P , and P interrogation pulses. “S” indicates ERP of S suppression pulse. “S I” means tha t the S ERP is 2 dB less than the interrogati on ERP. “S I” means t hat the S ERP is 3 dB less than the interrogation ERP. In steps 24, 63, 64, 79 and 83, no S pulses are transmit ted. STEP NUMBER MTL (-dBm) INTERFERENCE LIMITING PRIORITY MINIMUM EFFECTIVE RADIATED INTERROGATION POWER (dBm) .. .. . S S I I... S S I I... S S I I... S S I I... S S I I... S S I I... S S I I... S S S S I I I I .. ... . ... . .. 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 ATT-14 Figure A-2a. Example of high-density whisper-shout sequence (con’t) LEFT & RIGHT DIRECTIONS 25, 26 27, 28 29, 30 31, 32 33, 34 35, 36 37, 38 39, 40 41, 42 43, 44 45, 46 47, 48 49, 50 51, 52 53, 54 55, 56 57, 58 59, 60 61, 62 63, 64 S I I TOP ANTENNA TOP ANTENNA EFFECTIVE RADIATED POWER (dBm) NOTES.— “I” indicates ERP of P , P , and P interrogation pulses. “S” indicates ERP of S suppression pulse. “S I” means tha t the S ERP is 2 dB less than the interrogati “S I” means t hat the S ERP is 3 dB less than the interrogatio In steps 24, 63, 64, 79 , no S pulses are transmitted. and 83 STEP NUMBER MTL (-dBm) INTERFERENCE LIMITING PRIORITY MINIMUM EFFECTIVE RADIATED INTERROGATION POWER (dBm) .. S S I I... S S I I... S S I I... S S I I... S S I I... S S I I... S S I I... S S S S I I I I .. ... . AFT DIRECTION S I I.. S S I I... S S I I... S S I I... S S I I... S S I I... S S I I... S I. . .. 2, 3 6, 7 10, 11 14, 15 18, 19 22, 23 26, 27 30, 31 34, 35 38, 39 42, 43 46, 47 50, 51 54, 55 58, 59 62, 63 65, 66 68, 69 71, 72 74, 75 BOTTOM OMNI ANTENNA S I I.. .. S S I I.. .. 2007/70/II. szám Attachment Annex 10 — Aeronautical Telecommunications ATT-15 28/11/02 Figure A-2b. Example of low-density whisper-shout sequence S S S S S I I I I I I Forward Direction Top Antenna Note.— Each 1 dB reduction in the sequence follows the priority for the forward beam in Figure A-2a. 7, 8 9, 10 11, 12 13, 14 15, 16 S S S S S S S I I I I I I I I I I I I I Top Antenna Top Antenna Left & Right Direction Note.— Each 1 db reduction in the sequence follows the priority for the right/left beam in Figure A-2a. Note.— Each 1 db reduction in the sequence follows the priority for the rear beam in Figure A-2a. Note.— Each 1 db reduction in the sequence follows the priority for the bottom beam in Figure A-2a. MIN EFFECTIVE RADIATED POWER (dBm) NOTES.— “I” indicates ERP of P , P , and P interrogation pulses. “S” indicates ERP of S suppression pulse. “S I” means th a t the S ERP is 3 dB less than the interrogat “S I” mea ns that the S ERP is 10 dB less than the interr ogation ERP. In the last steps of each quadrant, no S pulses are transmit ted. STEP NUMBER MTL (-dBm) INTERFERENCE LIMITING PRIORITY MINIMUM EFFECTIVE RADIATED INTERROGATION POWER (dBm) Rear Direction Bottom Omni S S S .. .. ... .. .. 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 ATT-16 omnidirectionally. If a directional-receive antenna is used, the MTL values must be adjusted to account for the antenna gain. For example, for a net antenna gain of 3 dB, all MTL values in the table would be raised by 3 dB; and the MTL for step number 1 would be –71 dBm rather than –74 dBm. 3.2.2.5 The power is defined as the effective radiated power for the interrogation. All power levels are to be within ±2 dB of nominal. The tolerance of the step increments is to be ±1/2 dB and the increments are to be monotonic throughout the entire power range of the sequence. 3.2.2.6 Most of the interrogations are transmitted from the top antenna because it is less susceptible to multipath interference from the ground. 3.2.2.7 Selection of the appropriate whisper-shout subsequence for a particular antenna beam is performed each interrogation cycle based on the current or anticipated level of Mode A/C synchronous garble in that beam as determined by ACAS surveillance. The high density whisper-shout subsequence is selected for an antenna beam whenever synchronous garble is present in that beam as evident from the existence of at least one low confidence altitude code bit in two consecutive Mode C replies. The 6-level whisper-shout sequence is selected for an antenna beam if either:

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