Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4892

d) the vertical separation that would be achieved at closest approach if both aircraft were to level off exceeds Zlosep. 4.4.4.4.1 The vertical speed limit 0 ft/min RA generated in accordance with 4.4.4.4 is retained if neither aircraft accelerates vertically toward the other with a change in rate in excess of Ôl. Otherwise, the reference logic will immediately generate a climb or descend RA as appropriate for the RA sense. 4.4.4.4.2 The value 6 m/s (1 000 ft/min) is used for Ôlo. The value 244 m (800 ft) is used for Zlosep. 5. ACAS II USE OF HYBRID SURVEILLANCE TECHNIQUES 5.1 Overview 5.1.1 Hybrid surveillance is the technique used by ACAS to take advantage of passive position information available via extended squitter. Using hybrid surveillance, ACAS validates the position provided by extended squitter through direct active range measurement. Initial validation is performed at track initiation. Revalidation is performed once per 10 seconds if the intruder becomes a near threat in altitude or range. Finally, regular once-per-second active surveillance is performed on intruders that become a near threat in both altitude and range. In this manner, passive surveillance (once validated) is used for non-threatening intruders thus lowering the ACAS interrogation rate. Active surveillance is used whenever an intruder becomes a near threat in order to preserve ACAS independence as an independent safety monitor. A block diagram of the hybrid surveillance algorithm is presented in Figure A-11. 5.1.2 The reported altitude in the extended squitter position report is loaded within the Mode S transponder from the same source used to provide the altitude reported in the reply to an ACAS addressed interrogation. The altitude reported in an extended squitter position report may therefore be used to update the altitude of a track undergoing active surveillance, in the event that the transponder fails to reply to active interrogations. 5.2 Hybrid surveillance equipment characteristics 5.2.1 INITIAL VALIDATION 5.2.1.1 A passive track is initiated by the receipt of an extended squitter with a 24-bit address that is not in the track file, nor is associated with a track undergoing active surveillance. This latter case can occur if the short squitter established an active track before an extended squitter containing position reports is received. 5.2.1.2 ACAS will handle an extended squitter acquisition the same way that it handles a short squitter acquisition. After receiving the required number of squitters at the ACAS MTL (the same number as specified for short squitters in Chapter 3, 3.1.2.8.5), an attempt is made at active surveillance for a prescribed number of times. A successful reply will lead to track acquisition. An unsuccessful attempt will lead to discarding acquisition for this aircraft address, since the ADS data could not be validated. Continued receipt of extended squitters will lead to a subsequent acquisition attempt. 5.2.1.3 In the case of an aircraft providing extended squitter information, a successful acquisition reply will provide the opportunity to validate the information. But in either case (short or long squitter), the same criteria for track acquisition are followed, in terms of the number of correlating squitters that are required and the number of interrogation attempts that are made. 5.2.1.4 Initial ADS information validation is performed at passive track initiation to determine if the track can be maintained on passive data. An active surveillance measurement is made using a short addressed interrogation which carries an ACAS cross-link command to provide the contents of register 05[HEX] (extended squitter airborne position) in the reply. The reply to this interrogation also provides the aircraft speed capability and the reported barometric altitude in addition to the ADS-B airborne position report. The relative range and bearing computed from own and intruder reported positions is compared to the active range and bearing measurements and the altitude provided in the position report is compared to the altitude obtained from the active interrogation. If the reported information does not agree with the range, bearing or altitude obtained via the active interrogation within limits recommended in Chapter 4, 4.5.1.3.2, the track is declared to be an active track and future extended squitters from this aircraft are ignored by ACAS. 5.2.2 REVALIDATION AND MONITORING If the following condition is met for an aircraft with a relative altitude ≤ 10 000 ft: (Intruder altitude difference ≤ 3 000 ft OR vertical TAU to 3 000 ft ≤ 60 seconds) OR 2007/70/II. szám Attachment Annex 10 — Aeronautical Telecommunications ATT-49 28/11/02 Figure A-11. ACAS hybrid surveillance algorithm TRACK INITIATION INTERROGATE TO VALIDATE RELATIVE RANGE AND BEARING PASSED TRACK UPDATE PASSIVE SURVEILLANCE (ALTITUDE DIFFERENCE Ç Ç Ç Ç 3 000 FEET OR VERTICAL TAU TO 3 000 FT 60 S) OR (RANGE 3 NM OR RANGE TAU TO 3 NM 60 S) (ALTITUDE DIFFERENCE Ç Ç Ç Ç 3 000 FEET OR VERTICAL TAU TO 3 000 FT 60 S) AND (RANGE 3 NM OR RANGE TAU TO 3 NM 60 S) REVALIDATION/MONITORING INTERROGATE ONCE/10 S ACTIVE SURVEILLANCE ACAS CROSS LINK VALIDATE RANGE RATE THREAT DECLARATION ACTIVE SURVEILLANCE ACAS CROSS LINK COORDINATION TRACK DROP TRACK DROP TRACK DROP TRACK DROP FAILED FAILED ACTIVE SURVEILLANCE ACTIVE SURVEILLANCE 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 ATT-50 (Range difference ≤ 3 NM OR range TAU to 3 NM ≤ 60 seconds) an active interrogation is made every 10 seconds to continuously revalidate and monitor the position reports. Any detected difference will result in the aircraft being declared an active track. 5.2.3 ACTIVE SURVEILLANCE If the following condition is met for an aircraft with a relative altitude ≤ 10 000 ft: (Intruder altitude difference ≤ 3 000 ft OR vertical TAU to 3 000 ft ≤ 60 seconds) AND (Range difference ≤ 3 NM OR range TAU to 3 NM ≤ 60 seconds) the aircraft is declared an active track and is updated on active range measurements once per second. 5.2.4 THREAT EVALUATION DECLARATION If the intruder aircraft is declared to be a threat or potential threat, active range measurement continues. 6. PERFORMANCE OF THE COLLISION AVOIDANCE LOGIC 6.1 Purpose of the performance requirements 6.1.1 The ACAS collision avoidance logic is the part of ACAS that receives information relating to identified intruders (i.e. any aircraft for which ACAS has established a track) and generates collision avoidance advisories on the basis of that information. In any ACAS equipment it is likely to take the form of software residing in a microprocessor and this software will implement a collection of mathematical algorithms. These algorithms might vary from one ACAS to another and the purpose of the performance requirements for the collision avoidance logic is to ensure that the performance of the mathematical algorithms is acceptable. 6.1.2 The development of the collision avoidance algorithms and their implementation as software are thought of as separate processes and these standards relate to the algorithms, even though, in practice, the software used to demonstrate that the algorithms are satisfactory might be closely related to that installed with ACAS. The performance requirements for the collision avoidance logic are not intended to guarantee that the collision avoidance software is satisfactory as software, though they are an essential ingredient of such a guarantee. Satisfactory performance of the software is to be achieved by using sound software engineering practices to ensure that the algorithms are implemented reliably. 6.1.3 The interoperability of the collision avoidance logics in any two equipments is achieved by ensuring that their RAs are consistent and that either RA alone is sufficient for the purpose of the system as a whole. Consistency is ensured by the requirements relating to coordination (Chapter 4, 4.3.5.5.1, 4.3.5.8 and 4.3.6.1.3). That either RA is sufficient is guaranteed by the collision avoidance logic performance requirements and, in particular, the requirement of satisfactory performance when the other aircraft is ACAS equipped but does not cooperate (Chapter 4, 4.4.2.1 j) 2)). 6.1.4 The performance requirements are intended to provide a global guarantee that the ACAS logic in question has an overall performance that is comparable with or superior to that of other ACAS logics. They do not describe the performance of the logic in any particular airspace. For many purposes, the best method of determining or studying the performance of an ACAS logic in a particular airspace is by means of simulations based on ATC ground radar data. This possibility is discussed further in 6.4.4. 6.2 Conditions under which the requirements apply 6.2.1 COMMENT The conditions given in Chapter 4, 4.4.2 are specified in order to define the subsequent requirements, but satisfactory performance is required in all normal operating conditions. This is to be demonstrated by varying the conditions in which the performance measures are calculated in a way that reflects the normal variations that might be expected and ensuring that the calculated performance measures are robust, i.e. that they do not degrade sharply as the conditions assumed deteriorate. 6.2.2 SURVEILLANCE ERRORS 6.2.2.1 Surveillance errors can take a number of forms:

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