TCAS & GPS PDF

1 Chapter 10 TRAFFIC ALERT & COLLISION AVOIDANCE (TCAS) SYSTEM GLOBAL POSITIONING SYSTEM (GPS)  2 Learning Outcomes  Basic operation of TCAS  Working of the control and monitor systems of TCAS  Principle operation of GPS  Wor...

1 Chapter 10 TRAFFIC ALERT & COLLISION AVOIDANCE (TCAS) SYSTEM GLOBAL POSITIONING SYSTEM (GPS)  2 Learning Outcomes  Basic operation of TCAS  Working of the control and monitor systems of TCAS  Principle operation of GPS  Working of the control and monitor systems of the GPS  GPS Indicator  3 Introduction  Traffic Alert and Collision Avoidance System (or TCAS) is a computerized avionics device which is designed to reduce the danger of mid-air collisions between aircraft  It monitors the airspace around an aircraft, independent of air traffic control, and warns pilots of the presence of other aircraft which may present a threat of Mid Air Collision (MAC)  4 Introduction  Airborne Collision Avoidance System mandated by International Civil Aviation Organisation (ICAO) to be fitted to all aircraft over 5700 kg or authorized to carry more than 19 passengers  In modern aircraft, the TCAS display may be integrated in the Navigation Display, in older cockpit aircraft TCAS display is Vertical Speed Indicator (VSI) which indicates the speed with which the aircraft is climbing or descending  5 2 4 1 0.5 6 0 1000 FEET PER MINUTE 6 5 0. 4 1 2 Vertical Speed Indicator  6 TCAS Operation  TCAS involves communication between all aircraft equipped with an appropriate transponder  Each TCAS equipped aircraft interrogates all other aircraft in a determined range about their position (via 1030 MHz), and all other aircraft reply to interrogation (via 1090 MHz)  Interrogation-and-response cycle may occur several times per second, by which the TCAS system builds a three dimensional map of aircraft in the airspace, incorporating their bearing, altitude and range  7 TCAS Operation  By extrapolating current range and altitude difference to anticipated future values, it determines if a potential collision threat exists  Primary Surveillance Radar (PSR) was first used to support ATC in the late 1940s  PSR displays to the controller the plan view position of aircraft, however it does not know the Identity or Altitude of aircraft  8 TCAS Operation  Secondary Surveillance Radar (SSR) interacts with a Transponder carried on each aircraft. SSR interrogates the transponder to downlink Identity (Mode A) and Altitude (Mode C) information or more comprehensive data including Identity and Altitude (Mode S)  TCAS is a mini SSR on aircraft It is perpetually scanning the sky around own aircraft searching for proximate aircraft to ensure sufficient time for avoidance action in a high speed head to head encounter  9 Aural Annunciation Coordination EFIS or TCAS Display TCAS Mode S Unit XPDR Radar Altimeter Air Data Gears & TCAS + SSR Computer Flaps Control Panel Radar Altimeter Lower TCAS Mode S Antenna Antenna Antenna TCAS Block Diagram  10 TCAS Operation  TCAS has a minimum surveillance range of 40 nautical miles  Top and bottom antennas are used to ensure threat aircraft above and below are detected  The static, electronically steered antennas used to measure the position of proximate aircraft with a range accuracy of 1/125 nautical miles and a bearing accuracy of 3 degrees  Antennas operate at temperatures between -600 C and 1000 C at air speeds up to 600 knots  11 TCAS Operation  TCAS is constantly interrogating Mode C (Altitude) Transponders in proximate aircraft respond with Altitude information  The range is determined from the time elapsed between interrogation and reply, bearing is determined by the directional antenna and altitude is received in the reply from the other aircraft’s altitude encoder  It can be seen that TCAS will not detect aircraft which do not have a functioning Mode A/C or Mode S transponder  12 TCAS Symbols Non Threat Traffic which is not a threat will appear initially as an open white diamond on the display, It means that traffic is more than 6 nm range or more than 1200 ft vertically separation from given aircraft  13 TCAS Symbols Proximate Traffic which is the traffic within 6 nm range indicated by solid diamond with relative altitude annotation, but the computer calculates it is still not a threat +12  14 TCAS Symbols Traffic Advisory (TA) if the computer calculates that the intruder is potentially hazardous, the symbol will change to a solid yellow circle A TA voice is annunciated as ‘Traffic Traffic’ -05  15 TCAS Symbols Resolution Advisory (RA) about 10-15 seconds later, if the intruder is assessed as an actual collision threat, the symbol will change to red square A voice command ‘Descend Descend’ with computed RA will be shown on the cockpit display +04  16 Human Machine Interface (HMI) Three main elements of the Human Machine Interface (HMI) are  Plan Position Display of traffic and threat aircraft  Aural Prompts for the required action  Display of Required Avoidance Manoeuvre  17 Human Machine Interface (HMI) Pilot Response to TA & RA:  In response to a Traffic Advisory, the Pilot is expected to attempt visual acquisition and prepare for any Resolution Advisory  In response to a Resolution Advisory, the Pilot is expected to recognize and enact the RA within 5 seconds. This requires a very high degree of trust in TCAS  Pilots are generally trained to obey ATC, however in the specific case of TCAS-RA and ATC instruction being in conflict, the RA must take priority  18 An Encounter – The Pilot’s View Non-threat traffic is shown with open white diamond in relative position to own aircraft on the TCAS display CMD 210 TRK M 20 20 10 10 18 24 10 10 20 20  19 An Encounter – The Pilot’s View Proximate Traffic is displayed similarly to non threat traffic but with the diamond is now filled. The aural warning ‘Traffic, Traffic’ is annunciated. Relative altitude is displayed next to the traffic, in this case the traffic is 300ft higher than own aircraft and level CMD 210 TRK M 20 20 10 10 18 24 +03 Traffic 10 10 20 20  20 An Encounter – The Pilot’s View Resolution Advisory symbol changes from a white diamond to a filled red square. The aural advisory ‘Descend, Descend’ is annunciated. A red trapezoid indicating forbidden aircraft pitch is displayed on the Flight Director. By changing the aircraft pitch to be outside the forbidden region, the required descent rate is achieved CMD 210 TRK M 20 20 10 10 18 24 Traffic +03 10 10 20 20  21 An Encounter – The Pilot’s View Descend Established pilot has initiated and established the required descend rate, indicated by the ‘nose’ of the aircraft now pointing down on the Flight Director CMD 210 TRK M 20 20 10 10 18 24 Traffic +04 10 10 20 20  22 An Encounter – The Pilot’s View Level Off descent has achieved the required vertical separation and own aircraft will pass safely below the threat aircraft CMD 210 TRK M 20 20 10 10 18 24 Traffic 10 10 +06 20 20  23 An Encounter – The Pilot’s View Clear of conflict two aircraft have passed and the distance between them is growing, the threat aircraft symbol becomes yellow. The aural advisory ‘Clear of Conflict’ is annunciated. Pilot will now initiate a climb to return the aircraft to the ATC assigned Flight Level CMD 210 TRK M 20 20 10 10 18 24 Traffic 10 10 +06 20 20  24 International Standardization  The Collision Avoidance System is required to work anywhere in the world and hence it is necessary that systems operate to agreed standards  TCAS is installed in some 20,000+ aircraft worldwide and has proven to add a significant reduction in collision risk  The commercial value of safety is reflected in the reduced insurance premium for TCAS equipped aircraft  25 Introduction  Global Positioning System (GPS), a process used to establish a position at any point on the globe, developed by the U.S. Department of Defence and can be used both by civilians and military personnel  Civil signal SPS (Standard Positioning Service) can be used freely by the general public, while the military signal PPS (Precise Positioning Service) only can be used by authorized government agencies  The first satellite was placed in orbit on 22nd February 1978, and there are currently 24 constellation of satellites (21 active + 3 spare) orbiting the earth at a height of 20,000 km on 6 different orbital planes  26 Working Principle of GPS Using GPS, the following two values can be determined anywhere on Earth  One’s exact location (Longitude, Latitude and Altitude) accurate to within a range of 20 m to approx.30 mm  Universal Time Coordinated (UTC) accurate to with in a range of 60 ns to approx.5 ns  Speed and Direction of travel can be derived from these coordinates as well as the time  27 Satellites Earth Longitude : 9°24' Latitude : 46°48’ Altitude : 709.1m Time : 12h33'07'' Working of GPS  28 Working Principle of GPS  Satellite orbits are inclined at 55° to the equator, ensuring that a least 4 satellites are in radio communication with any point on the planet  Each satellite orbits the Earth in approximately 12 hours and has four atomic clocks on board  Exact position of each satellite is known at any given time and the distance to each satellite can be calculated by GPS receiver  29 Working Principle of GPS  Exact satellite position data is transmitted to the receiver as part of the satellite message  Since distance equals velocity multiplied by time, the receiver need only measure the time it took for the GPS signal to reach the receiver  The speed at which the signal travelled to the receiver is a constant 3×108m/s. Using time and velocity to derive distance is known as the time of arrival ranging  30 Example 10-1 Two dimensional model of GPS user segment  In this case all satellites are located in one geometric plane, knowing the distance from just two satellites would provide the location of aircraft  Aircraft must be located somewhere on a circle with a radius of 30 km from satellite A, and somewhere on a circle with a radius 40 km from satellite B  In this two dimensional model the aircraft can be in one of two  31 Example 10-1  To further define the locations of our aircraft in the two dimensional model, a third GPS satellite is added  if the aircraft is 30 km from satellite A, 40 km from satellite B, and 20 km from satellite C, the aircraft must be in position #1  32 D=30 km D=V×ΔT Position #2 Satellite A Satellite B Position #1 D=40 km D=V×ΔT Using Two Satellites to Determine Position  33 D=30 km D=V×ΔT Position #2 Satellite A Satellite B Position #1 Satellite B D=40 km D=20 km D=V×ΔT D=V×ΔT Using Three Satellites to Determine Position  34 Example 10-2  If a user on the ground receives a satellite signal with a delay of 66.6 ms, what distance the satellite is located from the user? Dis tan ce Speed = Time −3 Dis tan ce = 3 10  66.6 10 8 = 19980  20,000km  35 GPS System Segments GPS consists of  Space Segment (SS)  Control Segment (CS)  User Segment (US)  36 Space Segment Navigational Data Tracking and Clock Update User Segment Control Segment GPS System Segments  37 Space Segment The space segment consists of all GPS satellites  Each satellite transmits position and precise time information on two frequencies known as L1 (civilian) and L2  L1 operates at 1575.42 MHz and L2 has an operating frequency of 12287.6 MHz. These signals are digitally modulated and have a bandwidth of 20 MHz  Digital modulation of the L1 carrier is achieved through a process known as Phase Modulation, with every change in the code data there is a change in the L1 carrier phase  38 GPS Satellite  39 Transmitted Carrier Frequency Satellite Signal 1575.42 MHz (Phase Modulation) L1 Carrier Code Generator Phase Modulation of GPS Signal  40 Control Segment  The control segment consists of Master Control Station (MCS) is in Colorado Springs and four unmanned stations in Hawaii, Kwajalein, Diego Garcia, and Ascension, which track the satellites and relay information to the MCS  The control segment monitors the satellites and updates their orbital parameters and clocks, also MCS computers analyze the data and provide correction signals as needed to the ground stations  41 MCS Colorado Springs Hawaii Kwajalein Ascension Diego Garcia Location of GPS Ground Facilities  42 User Segment  The GPS user segment consists of the GPS receivers and the user community  Four satellites are required to compute the four dimensions of X, Y, Z (position) and time  Navigation in three dimensions is the primary function of GPS. Navigation receivers are made for aircrafts, ships, ground vehicles, and for hand carrying by individuals  The information on the receiver display screen includes the destination on this leg, with distance to go and ground speed  43 GPS User WPT TRK 00 M DTK DIS WSSS 1010M 5NM RNG BRG N 1010M 33N 3 CTS WSSL PU 1450M 30N SEL D 6 ETA ZOOM 5:13LC 10NM PLA WSSS MEN WSAP U VSR WSAC 0 fs BED CLR TKE 780 WSAP WSSS ENT GS ETE XTK DEFAULT 0:00NM 50kn 00:06 NAV APR NAV GPS MSG NRST OBS MSG FPL TERR PROC PUSH CRSR GPS Receiver  44 GPS Applications  Most common airborne applications include navigation by general aviation and commercial aircraft  The Local Area Augmentation System  ILS-style display to use while flying a precision approach  45 GPS Errors  Satellite Clock Error is due to minor inaccuracies in synchronizing the satellite atomic clocks  Ephemeris Errors which are caused by slight variations in satellites position as it orbits the earth  Atmospheric Propagation Errors are caused by distortion of the transmitted signal as it travels from the satellite to the receiver. Most of these errors are created as the radio signals travel through the ionosphere  46 Ionospheric Error  47 GPS Errors  Receiver Errors are caused by local electrical noise, computational errors, and errors in matching the pseudorandom digital codes GPS ERRORS APPROXIMATE ERROR DISTANCE Satellite Clock Error 2 feet Ephemeris Error 2 feet Atmospheric 2 feet Propagation Error Receiver Error 4 feet  48 The End