Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4791

b) the difference between the measured image range rate and the calculated image range rate is less than or equal to 21 m/s (40 kt), where the calculated image range rate is either (for the single-reflection case): or (for the double-reflection case): where: ri is the image range, r is the real range, Z is the real altitude, for altitude reporting targets or Z is set to own altitude for non-altitude reporting targets, and Z0 is own altitude If a track is identified as an image, it may be retained, but it cannot be flagged as established for use by the threat detection logic. 3.1.2.10 Missing Mode A/C reports. The equipment continues to pass to the collision avoidance algorithms predicted position reports for Mode A/C targets for six surveillance update intervals following the receipt of the last valid correlating reply. The equipment does not pass position reports for more than six surveillance update intervals following the receipt of the last valid correlating reply unless the target again satisfies the surveillance initiation criteria of 3.1.2.8. 3.1.3 SURVEILLANCE OF INTRUDERS WITH MODE S TRANSPONDERS 3.1.3.1 Efficient air-air surveillance techniques have been developed for intruders equipped with Mode S transponders. Because of Mode S selective address, there is no synchronous garble associated with surveillance of Mode S transponders. However, multipath must be dealt with and the surveillance of Mode S transponders should be accomplished with as few interrogations as possible to minimize interference. 3.1.3.2 The Mode S modulation formats are inherently more resistant to multipath than are the Mode A/C modulation formats. However, the greater length of the Mode S transmission makes it more likely to be overlapped by multipath. The use of top-mounted antennas and variable receiver thresholds (to protect the Mode S reply preamble) increases the multipath resistance to an acceptable level for reliable air-air surveillance. The use of antenna diversity transponders on ACAS aircraft provides an additional reliability margin for coordination between pairs of conflicting ACAS aircraft. 3.1.3.3 Mode S interrogation rates are kept low by passive detection of transponder transmissions and by interrogating once per second only those intruders that could become immediate threats. Intruders that are not likely to become immediate threats should be interrogated less frequently (i.e. once every 5 seconds). Passive address acquisition prevents unnecessary interference with other elements of the SSR and ACAS system. ACAS listens to Mode S all-call replies (DF = 11, acquisition squitter transmissions, Chapter 3, 3.1.2.8.5.1 or DF = 17, extended squitter transmissions, Chapter 3, 3.1.2.8.6.1). These may occur in response to Mode S ground station all-call interrogations or as spontaneous transmission (called squitters) at intervals ranging from 0.8 to 1.2 seconds for the acquisition squitter, and at shorter intervals for the extended squitter. Reception of squitters may be alternated between the top and bottom antennas. If reception is switched, it will be necessary to control the switching times to avoid undesirable synchronism with the squitters transmitted by Mode S antenna diversity transponders. 3.1.3.4 The 24-bit aircraft address in the squitter is protected by error coding to ensure a high probability of obtaining a correct address. Since the squitter transmission does not contain altitude information, ACAS attempts to obtain altitude passively from Mode S replies generated in response to ground interrogations or interrogations from other ACAS aircraft. If altitude is not received shortly after address detection, the Mode S aircraft is actively interrogated to obtain altitude. 3.1.3.5 After ACAS has determined the altitude of a detected Mode S aircraft, it compares the altitude of this aircraft to its own altitude to determine whether or not the target can be ignored or should be interrogated to determine its range and range rate. If the measured range and the estimated range rate indicate that it is (or could soon be) a collision threat, the intruder should be interrogated once per second and the resulting track data fed to the collision avoidance algorithms. An aircraft at longer range should be interrogated only as often as necessary to maintain track and ensure that it will be interrogated once per second before it becomes a collision threat. 3.1.3.6 The use of passive detection in combination with altitude comparison and a less frequent interrogation of nonthreat intruders reduces the Mode S interrogation rate automatically when the local densities of other ACAS aircraft are very high. Therefore, a higher interrogation power level is available to improve surveillance performance. r· i r· i 2--  r·[ 2ri r – ---------------     + = 2ri r – ( )2 ([ r2 – Z0 Z – ( )2) 2-- Z· Z· + ( ) + rr· Z0 Z – ( ) Z· Z· – ( ) ] ] – + r· i ri ---   ri r2 – Z0 Z – ( )2 +     2-- Z· Z· + ( ) rr· Z0 Z – ( ) Z· Z· – ( ) – + = 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 ATT-10 3.1.3.7 MODE S SURVEILLANCE INITIATION 3.1.3.7.1 The equipment is intended to provide Mode S surveillance with a minimum of Mode S interrogations. The identity of Mode S targets is determined by passively monitoring transmissions received with DF = 11 or DF = 17. Error detection and correction is applied to the received squitters to reduce the number of addresses to be processed. The altitude of the Mode S targets from which a squitter has been received is determined by passive monitoring transmissions received with DF = 0 (short air-air surveillance replies, Chapter 3, 3.1.2.8.2) or DF = 4 (surveillance altitude replies, Chapter 3, 3.1.2.6.5) or active selective interrogations (air-air surveillance interrogation, Chapter 4, 4.3.8.4) and monitoring the corresponding air-air surveillance replies. The equipment monitors squitter and altitude replies whenever it is not transmitting, or receiving replies to, Mode S or Mode C interrogations. Each received reply is examined to determine what further action should be taken. 3.1.3.7.2 To reduce the number of unnecessary interrogations, a squitter target is not interrogated if so few squitters and altitude replies are received from it that no threat is indicated. Targets that might be a threat are called valid targets. The equipment is not intended to interrogate a target unless the altitude information indicates that it is within 3 050 m (10 000 ft) of own altitude. The ACAS aircraft interrogates targets from which it does not receive altitude information but does continue to receive error-free squitters. In order to establish timely acquisition of targets that transition the 3 050 m (10 000 ft) relative altitude boundary, the altitude of targets that are beyond 3 050 m (10 000 ft) of own altitude are monitored using unsolicited DF = 0 or DF = 4 replies, or in the absence of such replies, by periodically interrogating to elicit a DF = 0 reply. 3.1.3.7.3 The following is an example of one acceptable means of processing squitters and altitude replies to reduce unneeded interrogations:

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