Publication: Magyar Közlöny
Issue: MK-2009-104 (Year: 2009, Number: 104)
Era: 2004-2010
Section: 
Paragraph Index: 2581

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. Attachment Annex 10 — Aeronautical Communications ATT-55 22/11/07 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 (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. Annex 10 — Aeronautical Communications Volume IV 22/11/07 ATT-56 5.2.4 THREAT EVALUATION DECLARATION If the intruder aircraft is declared to be a threat or potential threat, active range measurement continues.

Source: https://magyarkozlony.hu/hivatalos-lapok/bfd0d67db9f223889f627fd618725b03526630e2/dokumentumok/d5234fd7275da04023366ab8a434989962a31bdf/letoltes