Airborne Collision Avoidance System (ACAS)

RADIOLOCATION J. Mateu - J. Berenguer RADIOLOCATION Airborne Collision Avoidance System (ACAS) Jordi Mateu – Jordi Berenguer RADIOLOCATION J. Mateu - J. Berenguer Course Contents I. Introduction to Air Navigation and Surveillance Functions. II. Pulsed Radar. III. Radar Clutter. IV. Doppler based Radars. V. Tracking Radars. VI. Secondary Surveillance Radar (SSR). VII. Automatic Dependent Surveillance (ADS). VIII.Airborne Collision Avoidance System (ACAS). IX. Enhanced Ground Proximity Warning Systems. X. Weather Radar. RADIOLOCATION J. Mateu - J. Berenguer Airborne Collision Avoidance System (ACAS) •The Airborne Collision Avoidance System (ACAS) II concept (realized as Traffic alert and Collision Avoidance System (TCAS) II equipment) is an airborne avionics system which acts independently of ATC as a last resort safety net to mitigate the risk of midair collision. •ACAS tracks aircraft in the surrounding airspace through the replies from their ATC transponders. •If the system diagnoses a risk of impending collision it issues a Resolution Advisory (RA)to the flight crew, which directs the pilots how best to regulate or adjust their vertical rate so as to avoid a collision. RADIOLOCATION J. Mateu - J. Berenguer Airborne Collision Avoidance System (ACAS) •ACAS II version 7.0 has been mandated in Europe since 1 January 2005 by all civil fixed-wing turbine-engined aircraft having a maximum takeoff mass exceeding 5700 kg or a maximum approved passenger seating configuration of more than 19. •Amendment 85 to ICAO Annex 10 (volume IV) published in October 2010 introduced a provision stating that all new ACAS installations after 1 January 2014 shall be compliant with version 7.1 and after 1 January 2017 all ACAS units shall be compliant with version 7.1. •In December 2011, the European Commission published an Implementing Rule mandating the carriage of ACAS II version 7.1 within European Union airspace earlier than the dates stipulated in ICAO Annex 10: from 1 December 2015 by all civil aircraft with a maximum certified take-off mass over 5700 kg or authorized to carry more than 19 passengers, with the exception of unmanned aircraft systems. RADIOLOCATION J. Mateu - J. Berenguer ACAS AND TCAS TCAS II is the only implementation that meets the ACAS ICAO Standards and Recommended Practices (SARPs). The term ACAS II is typically used when referring to the standard or concept and TCAS II when referring to the implementation. However, often both terms are used interchangeably. ACAS PRINCIPLES ACAS is designed to work both autonomously and independently of the aircraft navigation equipment and any ground systems used for the provision of air traffic services. Through antennas, ACAS interrogates the ICAO standard compliant transponders of aircraft in the vicinity. Based upon the replies received, the system tracks the slant range, altitude (when it is included in the reply message) and bearing of surrounding traffic. RADIOLOCATION J. Mateu - J. Berenguer ACAS ALERTS ISSUES ACAS can issue two types of alerts: •Traffic Advisories (TAs) –Helps the pilots in the visual acquisition of the intruder aircraft –Alerts them to be ready for a potential resolution advisory. •Resolution Advisories (RAs) –Are avoidance maneuvers recommended to the pilot. –An RA will tell the pilot the range of vertical rates within which the aircraft should be flown to avoid the threat aircraft. –An RA can be generated against all aircraft equipped with an altitude reporting transponder (Mode S or Mode A/C). –The intruder does not need to be fitted with ACAS II. –When the intruder aircraft is also fitted with an ACAS II system, both systems coordinate their RAs through the Mode S data link, in order to select complementary resolution senses. RADIOLOCATION J. Mateu - J. Berenguer RADIOLOCATION J. Mateu - J. Berenguer RADIOLOCATION J. Mateu - J. Berenguer RADIOLOCATION J. Mateu - J. Berenguer TCAS – Protected volume of airspace Time to go The range tau is equal to the slant range (nmi) divided by the closing speed (knots) multiplied by 3600. The vertical tau is equal to the altitude separation (feet) divided by the vertical closing speed of the two aircraft (feet/minute) times 60. RADIOLOCATION J. Mateu - J. Berenguer TCAS – Protected volume of airspace RADIOLOCATION J. Mateu - J. Berenguer TCAS II VERSION 7.0 •It was approved in December 1997 and became available at the beginning of 1999. •Version 7.0 further improved TCAS II compatibility with the air traffic control system. •The most significant enhancements brought by version 7.0 were: –The introduction of a horizontal miss distance filter; –25-foot vertical tracking; –Sophisticated multi-threat logic; –Compatibility with Reduced Vertical Separation Minima (RVSM) operations; –The reduction of electromagnetic interference; –Allowing RA reversals in coordinated encounters; –Simplified aural annunciations. RADIOLOCATION J. Mateu - J. Berenguer TCAS •Sistema independent del Control de Trànsit Aeri (ATC). •Es basa en la utilització dels transponders de Radar Secundari que incorporen les alters aeronaus. •Consisteix en interrogar les altres aeronaus, i calcular la seva distància i altitude, per: –Emetre alertes de peril: TRAFFIC ADVISORY (TA), (TCAS I i TCAS II) –Emetre resolucions de maniobra: RESOLUTION ADVISORY (RA), (TCAS II) RADIOLOCATION J. Mateu - J. Berenguer TCAS II – Block diagram •Directive antenna located at the top of the aircraft. –Transmit interrogations on 1030 MHz at varying power levels in each of four 90° azimuth segments. •Omnidirectional antenna located at the bottom of the aircraft –Transmits fewer interrogations and at a lower power than the top-mounted antenna. –These antennas also receive transponder replies, at 1090 MHz, and send these replies to the TCAS Processor. •Mode S/TCAS Control panel –Stand-by –Transponder –TA Only –Automatic or TA/RA •Mode S Transponder –Performs the normal functions as ATCRBS or a Mode S. –Provides air-to-air data exchange between TCAS-equipped aircraft so that coordinated, complementary RAs can be issued when required. –One antenna is mounted on the top of the aircraft while the other is mounted on the bottom. –These antennas enable the Mode S transponder to receive interrogations at 1030 MHz and reply to the received interrogations at 1090 MHz. –New transponder-TCAS integrated systems only require two antennas that are shared by the transponder and TCAS. •TCAS computer –performs airspace surveillance, intruder tracking, own aircraft altitude tracking, threat detection, RA maneuver determination and selection, and generation of advisories. –uses pressure altitude, radar altitude, and discrete aircraft status inputs •Traffic (TA) and Resolution (RA) announcements •Aural output messages •Traffic Display –Displayed traffic information also includes traffic vertical speed indications, and Proximate, TA, and RA status. RADIOLOCATION J. Mateu - J. Berenguer TCAS II – Block diagram RADIOLOCATION J. Mateu - J. Berenguer Antennas RADIOLOCATION J. Mateu - J. Berenguer Interrogation process RADIOLOCATION J. Mateu - J. Berenguer Garbling Due to the fact that the reply duration of a transponder is of 21 µs, a Synchronous Garbling can be created by all transponders within a radius of: R = 𝑐𝜏 2=21 · 10 · 3 · 10 2=𝟏, 𝟕 𝐧𝐦𝐢 The synchronous garbling can be reduced: •by slightly overlapping coverage. •by the use of the Mode C Only All Call interrogation, which inhibits Mode S transponders from replying to a Mode C interrogation. RADIOLOCATION J. Mateu - J. Berenguer Garbling The synchronous garbling can be reduced: –By slightly overlapping coverage, making directional interrogations in four 90° sectors, with the directive antenna. –By the use of the Mode C Only All Call interrogation, which inhibits Mode S transponders from replying to a Mode C interrogation. –By avoiding the initiation of surveillance tracks based on multipath replies, with Dynamic Minimum Triggering Level (DMTL). •The direct-path power level is used to raise the minimum triggering level (MTL) of the TCAS receiver enough to discriminate against the delayed and lower power reflections. •The 4-pulse direct reply is above the DMTL level, while the delayed, lower-power multipath reply is below the DMTL threshold, and is thus rejected by TCAS. RADIOLOCATION J. Mateu - J. Berenguer TCAS traffic display example: EFIS RADIOLOCATION J. Mateu - J. Berenguer TCAS RA display example: PFD & vertical speed tape RADIOLOCATION J. Mateu - J. Berenguer RA display example: IVSI combined with traffic display RADIOLOCATION J. Mateu - J. Berenguer RA aural alerts TCAS II version 7.0 RADIOLOCATION J. Mateu - J. Berenguer TCAS II – VERSION 7.1 RADIOLOCATION J. Mateu - J. Berenguer TCAS II – Change 7.1 RADIOLOCATION J. Mateu - J. Berenguer Version 7.1 EUROCONTROL mandate •In 2011, the European Commission published Regulation No 1332/2011, subsequently amended by Regulation No 2016/583, mandating, from 1 December 2015, the carriage of ACAS II (TCAS II) version 7.1 within European Union airspace by all civil airplanes with a MTOM exceeding 5700 kg or authorized to carry more than 19 passengers. •Aircraft not referred above, but which are equipped on a voluntary basis with ACAS II, must be equipped with version 7.1. The mandate does not apply to unmanned aircraft systems. AUR.ACAS.1005 Performance requirement (1) The following turbine-powered aeroplanes shall be equipped with collision avoidance logic version 7.1 of ACAS II: (a) Airplanes with a maximum certificated take-off mass exceeding 5.700 kg; (b) Airplanes authorized to carry more than 19 passengers. (2) Aircraft not referred to in point 1 which are equipped on a voluntary basis with ACAS II shall have collision avoidance logic version 7.1. (3) Point 1 shall not apply to unmanned aircraft systems. AUR.ACAS.1010 ACAS II training Operators shall establish ACAS II operational procedures and training programs so that the flight crew is appropriately trained in the avoidance of collisions and becomes competent in the use of ACAS II equipment.’ RADIOLOCATION J. Mateu - J. Berenguer TCAS II – Change 7.1 •In this instance aircraft A should climb at a rate that will take it out of the red zone and maintain a rate that is within the green zone. However, as the diagram shows, pilots can sometimes overreact and with the result that the vertical speed achieved exceeds that required to safely avoid the threat. Rates as high as 6,000 ft/min have been observed. •The maneuver shown may bring aircraft A into conflict with aircraft C. •The new ACAS II 7.1 version replaces the previous "adjust vertical speed, adjust" with the new "Level off, level off" RA and reduce instances of level busts and not induce conflict with the third party. RADIOLOCATION J. Mateu - J. Berenguer RA aural alerts TCAS II version 7.1 RADIOLOCATION J. Mateu - J. Berenguer TCAS II – Change 7.1 RADIOLOCATION J. Mateu - J. Berenguer TCAS II – Change 7.1 – Hybrid surveillance • Hybrid Surveillance further improves situational awareness and safety in the high density airspace and supports air traffic modernization efforts by reducing 1090 MHz frequency congestion. • Hybrid Surveillance allows the TCAS Traffic Computer to further reduce active interrogations by using intruder position data received via ADS-B equipped aircraft. • Hybrid Surveillance capability, which meets the qualification and requirements of the Hybrid Surveillance Minimum Operational Performance Standards (MOPS) document RTCA/DO-300, is identified as optional functionally within FAA TSO-C119c. RADIOLOCATION J. Mateu - J. Berenguer Hybrid surveillance