Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4821

h) The tracker provides upper and lower bounds within which the true altitude rate is expected to lie. The altitude rate bounds are used to determine if RA generation is to be delayed and in assessing the need for a sense reversal when the altitude rate confidence is “low”. 3.5.10 AIR-AIR COORDINATION 3.5.10.1 Coordination interrogations. When ACAS declares a similarly equipped intruder to be a threat, interrogations are transmitted to the latter for RA coordination via the Mode S data link. These interrogations, which contain resolution messages, are made once per processing cycle as long as the intruder remains a threat. The equipped threat always acknowledges receipt of a resolution message by transmitting a coordination reply. 3.5.10.2 COORDINATION INTERROGATION 3.5.10.1 PROCESSING 3.5.10.2.1 ACAS processes a resolution message received from another ACAS-equipped intruder by storing the RAC for that intruder and by updating the RAC record. 3.5.10.2.2 RAC is a general term that is used to mean a vertical RAC (VRC) and/or a horizontal RAC (HRC) as appropriate. Specifically, the information provided in the Mode S interrogation is the VRC for ACAS II and the VRC and/or HRC for ACAS III. 3.5.10.2.3 The RAC record is a composite of all currently active RACs (VRCs and/or HRCs) that have been received by ACAS. The four bits in the RAC record correspond to the two VRC values (“do not pass below” and “do not pass above”) followed by the two HRC values (“do not turn left” and “do not turn right”). If a bit in the RAC record is set, it means that the corresponding RAC has been received from one or more ACAS. Each time an RAC is received from another ACAS, the corresponding bit(s) in the RAC record is (are) set. Each time an RAC cancellation is received from another ACAS, the corresponding bit(s) is (are) cleared so long as no other ACAS is also currently causing the bit(s) to be set. 3.5.10.3 COORDINATION SEQUENCE The sequence of coordination messages and associated processing is illustrated in Figure A-9. Failure to complete the coordination may result in the choice by the threat of an incompatible RA sense. 3.5.10.4 COORDINATION PROTOCOL 3.5.10.4.1 After declaring an equipped intruder to be a threat, ACAS first checks to see if it has received a resolution message from that threat. If so, ACAS selects an RA that is compatible with the threat’s vertical sense. If not, ACAS selects an RA based on the geometry of the encounter (3.5.2). In either case, ACAS begins to transmit vertical sense information to the threat once per scan in the form of an RA complement in a resolution message. The RA complement is “don’t pass above” when ACAS has elected to pass above the threat and “don’t pass below” when ACAS has elected to pass below the threat. Figure A-9. Coordination sequence Own ACAS Other ACAS aircraft ... Store RAC for this threat ... Update RAC record Resolution message Coordination reply message Wait 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 ATT-34 3.5.10.4.2 Upon detecting ACAS as a threat, the threat goes through a comparable process. If for any reason the two aircraft select the same (incompatible) separation sense, the aircraft with the higher 24-bit aircraft address reverses its sense. This could happen if the two aircraft detect each other as threats simultaneously or if there were a temporary link failure preventing successful communication. 3.5.10.5 COORDINATION DATA PROTECTION ACAS stores the current RA and the active RAC(s) received from other ACAS-equipped aircraft that perceive own aircraft to be a threat. In order to ensure that the stored information is not modified in response to one or more ACAS while it is being used for RA selection by own ACAS, the data must be protected so that it is available to, or capable of being modified in response to, only one ACAS at a time. For example, this may be accomplished by entering the coordination lock state whenever the data store is accessed by own ACAS or offered new data from a threat ACAS. If a resolution message is received while the coordination lock state is active, the data is held until the current coordination lock state is ended. The potential for simultaneous data access by different processes within ACAS exists because incoming threat resolution messages are received asynchronously to the ACAS processing, effectively interrupting this processing. 3.5.11 GROUND COMMUNICATION 3.5.11.1 Report of ACAS resolution advisories to the ground. Whenever an RA exists, ACAS indicates to the aircraft’s Mode S transponder that it has an RA report available for a Mode S ground station. This causes the transponder to set a flag indicating that a message is waiting to be transmitted to the ground. Upon receipt of this flag a Mode S sensor may request transmission of the RA report. When this request is received, own Mode S transponder provides the message in a Comm-B reply format. In addition, ACAS generates periodic broadcasts at 8-second intervals for the time during which an RA is indicated to the pilot. The broadcast reports the last values taken by the parameters of the RA during the previous 8-second period even if the advisory has been terminated. This allows ACAS RA activity to be monitored in areas where Mode S ground station surveillance coverage does not exist by using special RA broadcast signal receivers on the ground. RA broadcasts are normally destined for ground equipment but are defined as uplink transmissions. 3.5.11.2 Ground station control of threat detection parameters. Threat detection parameters can be controlled by one or more Mode S ground stations by transmitting interrogations containing sensitivity level control (SLC) command messages addressed to the ACAS aircraft. Upon receipt of an SLC command message from a given Mode S ground station, ACAS stores the SLC command value indexed by ground station number. ACAS uses the lowest of the values received if more than one ground station has sent such a message. ACAS times out each site’s SLC command separately and cancels it if it is not refreshed by another message from that site within 4 minutes. ACAS can also immediately cancel an SLC command from a ground station if a specified cancellation code is received from that station. SLC commands cannot be used within linked Comm-A interrogations. 3.5.12 SENSITIVITY LEVEL CONTROL Control of the ACAS threat detection parameters can be effected by means of SLC commands provided as follows:

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