Aviation Communication, Navigation, and Surveillance (CNS)

1. Aviation Communication, Navigation, and Surveillance (CNS) Instructor: Dr. George L. Donohue Prepared by: Arash Yousefi Spring 2002

2. Summary • Chapter 7: Attitude and Heading References • Chapter 8: Doppler and Altimeter Radars • Chapter 9: Mapping & Multimode Radars • Chapter 10: Landing Systems • Chapter 11: Data Links and digital communication • Chapter 1: Introduction to CNS • Chapter 2: The Navigation Equations • Chapter 3: Terrestrial Radio-Navigation Systems • Chapter 4: Satellite Radio Navigation • Chapter 5: Terrestrial Integrated Radio Communication-Navigation Systems • Chapter 6: Air-Data Systems

3. Chapter One Introduction

4. Vy X Vx Vz Y Z Definitions • Navigation: the determination of the position and velocity of a moving vehicle. The process of measuring and calculating state vector onboard • Surveillance or Position Reporting: the process of measuring and calculating state vector out side the vehicle • Navigation sensor: may be located in the vehicle, in another vehicle, on the ground , or in space Six- component state vector

5. Definitions • Automatic Dependent Surveillance(ADS): reporting of position, measured by sensors in an aircraft, to a traffic control center. • Guidance: handling of the vehicle. Two Meanings; • Steering toward a destination of known position from the aircraft’s present position • Steering toward a destination without explicitly measuring the state vector (mostly military arcfts)

6. Categories of Navigation • Radio Systems:consist of a network of transmitters(sometimes also receivers) on the ground, satellite or on other vehicle. • Celestial Systems:compute position by measuring the elevation and azimuth of celestial bodies relative to the navigation coordinate frame at precisely known times. • Mapping Navigation Systems:observe images of the ground, profile of altitude, or other external features.

7. Dead-reckoning navigation systems • Derive their state vector fro, a continuous series of measurements relative to an initial position. Two kinds: • Acft heading & either speed or acceleration. • Gyroscopes or magnetic compassesheading • Air-data sensors or Doppler radar speed • Inertial sensorsvector acceleration • Emissions from continues-wave radio stations • Create ambiguous “lanes” that must be counted to keep track of coarse position

8. The Vehicle (1) • Civil Aircraft:mostly operate in developed areas(Ground-based radio aids are plentiful) • Air Carriers: large acft used on trunk routes and small acft used in commuter service. • General Aviation(GA): range from single-place crop dusters to well-equipped four-engine corporate jets.

9. The Vehicle (2) • Military Aircraft • Interceptors & combat air patrol:small, high-climb-rate protecting the homeland • Close-air support: mid-size to deliver weapons in support of land armies • Interdiction: mid-size and large acft to strike behind enemy lines to attack ground targets • Cargo Carriers: same navigation requirements as civil acft • Reconnaissance acft: collect photograph • Helicopter & short take of and landing(STOL) vehicle • Unmanned air vehicle

10. The Vehicle (3) • Fig 1.1 Avionics Placement on multi-purpose transport

11. Phases of Flight • Takeoff • Terminal Area • En-Route • Approach • Landing • Surface • Weather

12. Navigation Phases

13. Navigation Phases Picture courtesy of MITRE Corporation

14. Takeoff Navigation • From taxiing into runway to climb out • Acft is guided along the runway centerline by hand-flying or a coupled autopilot based on steering signals • Two important speed measurements are made on the runway • The highest ground speed at which an aborted takeoff is possible pre-computed and compared, during the takeoff run, to the actual ground speed as displayed by navigation system • The airspeed at which the nose is lifted is pre-calculated and compared to the actual airspeed as displayed by the air-data system

15. Terminal Area Navigation • Departure:begins from maneuvering out the runway, ends when acft leaves the terminal-control area • Approach: acft enters the terminal area, ends when it intercepts the landing aid at an approach fix • Standard Instrument Departure (SIDs) & Standard Terminal Approach Route (STARs) • Vertical navigation Barometric sensors • Heading vectors  Assigned by traffic controller

16. En Route Navigation • Leads from the origin to the destination and alternate destinations • Airways are defined by navaids over the land and by lat/long over water fixes • The width of airways and their lateral separation depends on the quality of the navigation system • From 1990s use of GPS has allowed precise navigation • In the US en-route navigation error must be less than 2.8 nm over land & 12 nm over ocean

17. Approach Navigation • Begins at acquisition of the landing aid until the airport is in sight or the acrft is on the runway, depending on the capabilities of the landing aid • Decision height (DH): altitude above the runway at which the approach must be aborted if the runway is not in sight • The better the landing aids, the lower the the DH • DHs are published for each runway at each airport • An acrft executing a non precision approach must abort if the runway is not visible at the minimum descent altitude (typically=700 ft above the runway)

18. Landing Navigation • Begins at the DH ends when the acrf exits the runway • Navigation may be visual or navigational set’s may be coupled to a autopilot • A radio altimeter measures the height of the main landing gear above the runway for guiding the flare • The rollout is guided by the landing aid (e.g. the ILS localizer)

19. Missed Approach • Is initiated at the pilot’s option or at the traffic controller’s request, typically because of poor visibility. And alignment with the runway • The flight path and altitude profile are published • Consists of a climb to a predetermined holding fix at which the acrf awaits further instructions • Terminal area navaids are used

20. Surface Navigation • Acrf movement from the runway to gates, hanger • Is visual on the part of the crew, whereas the ground controller observes acrf visually or with surface surveillance radar • GPS reports from acrfs that concealed in radar shadows reduce the risk of collision

21. Weather • Instrument meteorological conditions (IMC) are weather conditions in which visibility is restricted, typically less than 3 miles • Acft operating in IMC are supposed to fly under IFR

22. Design Trade-Offs (1) • Cost • Construction & maintenance of transmitter stations Government Concern • Purchase of on-board HW/SWUser Concern • Accuracy of Position & velocity • Specified in terms of statistically distribution of errors as observed on a large # of flights • Civil air carrier Based on the risk of collision • Landing error depends on runway width, acft handling characteristics, flying weather

23. Design Trade-Offs (2) • Autonomy:The extent to which the vehicle determines its own position & velocity without external aids. Subdivided to; • Passive self-contained systems neither receive nor transmit electromagnetic signals (dead-reckoning systems such as inertial navigators • Active self-contained systems Radiate but do not receive externally generated signals(radars, sensors). Not dependent on existence of navigation stations

24. Design Trade-Offs(3) (continue form previous slide) • Natural radiation receivers  i.e. magnetic compasses, star trackers, passive map correlators • Artificial radiation receivers measure electromagnetic radiation from navaids(earth or space based) but do not transmit (VOR, GPS) • Active radio navaidsexchange signals with navigation stations(i.e. DME, collision-avoidance systems). The vehicle betrays its presence by emitting & requires cooperative external stations. The least autonomous of navigation systems

25. Design Trade-Offs (4) • Latency • Time delay in calculating position & velocity, caused by computational & sensor delays • Can be caused by computer-processing delays, scanning by a radar beam, or gaps in satellite coverage • Geographic coverage • Terrestrial radio systems operating below approximately 100 KHz can be received beyond line of sight on earth; those operating above 100 KHz are confirmed to line of sight

26. Design Trade-Offs (5) • Automations • The crew receive a direct reading of position, velocity, & equipment status, without human intervention • Availability • The fraction of time the system is usable • Scheduled maintenance, equipment failure, radio-propagation problems • i.e 0.99 HRS Outage/YR for voice communication • System capacity • Reliability • Maintainability

27. Design Trade-Offs (6) • Ambiguity • The identification, by the navigation system, of two or more possible positions of the acft, with no indication of which is correct • Integrity • Ability of the system to provide timely warning to acft when its error are excessive • For en-route an alarm must be generated within 30sec of the time a computed position exceeds its specified error

28. Evolution of Air Navigation ADS-B GPS 1935, an airline consortium opened the first Airway Traffic Control Station 1922 ATC begins 1940s Impact of radar 1930 Control Tower Airway Centers 1960s & 70s Page 11-15 Katon, Fried

29. Integrated Avionics Subsystems (1) • Navigation • Communication • intercom among the crew members & one or more external two-way voice & data links • Flight control • Stability augmentation & autopilot • The former points the airframe & controls its oscillations • The latter provides such functions as attitude-hold, heading-hold, altitude hold • Engine control • The electronic control of engine thrust(throttle management)

30. Integrated Avionics Subsystems (2) • Flight management • Stores the coordinates of en-route waypoints and calculates the steering signals to fly toward them • Subsystem monitoring & control • Displays faults in all subsystems and recommends actions to be taken • Collision-avoidance • Predicts impending collision with other acft or the ground & recommends an avoidance maneuver

31. Integrated Avionics Subsystems (3) • Weather detection • Observes weather ahead of the acft so that the route of flight can be alerted to avoid thunderstorms & areas of high wind shears • Sensors are usually radar and laser • Emergency locator transmitter(ELT) • Is triggered automatically on high-g impact or manually • Emit distinctive tones on 121.5, 243, and 406 MHz

32. Architecture (1) • Displays; • Present information from avionics to the pilot • Information consists of vertical and horizontal navigation data, flight-control data (e.g. speed and angle of attack), and communication data (radio frequencies)

33. Architecture (2) • Flight controls; • The means of inputting information from the pilot to the avionics • Traditionally consists of rudder pedals and a control-column or stick • Switches are mounted on the control column, stick, throttle, and hand-controllers

34. Architecture (3) • Computation; • The method of processing sensor data • Two extreme organizations exist: • Centralized; Data from all sensors are collected in a bank of central computer in which software from several subsystems are intermingled • Decentralized; Each traditional subsystem retains its integrity

35. Architecture (4) • Data buses • Copper or fiber-optics paths among sensors, computers, actuators, displays, and controls • Safety partitioning • Commercial acft sometimes divide the avionics to; • Highly redundant safety-critical flight-control system • Dually redundant ,mission-critical flight-management system • Non-redundant maintenance system • Military acrft sometimes partition their avionics for reason other than safety

36. Architecture (5) • Environment • Avionics equipment are subject to; • acft-generated electricity-power transient, whose effects are reduced by filtering and batteries, • externally generated disturbances from radio transmitters, lightening, and high-intensity radiated fields • The effect of external disturbances are reduced by • shielding metal wires and by using fiberoptic data buses • add a Faraday shielding to meal skin of the acft

37. Architecture (6) • Standards • Navaid signals in space are standardized by ICAO • Interfaces among airborne subsystems, within the acft, are standardized by Aeronautical Radio INC. (ARINC), Annapolis Maryland, a nonprofit organization owned by member airlines • Other Standards are set by: • Radio Technical Commissions for Aeronautics, Washington DC • European Organization for Civil Aviation Equipment (EUROCAE) • etc.

38. Human Navigator • Large acft often had (before 1970) a third crew member, flight engineer: • To operate engines and acft subsystems e.g. air conditioning and hydraulics) • Use celestial fixes for positioning • Production of cockpits with inertial, doppler, and radio equipments facilitated the automatically stations selection, position/waypoint steering calculations and eliminated the number of cockpit crew to two or one.

39. Chapter Two The Navigation Equations

40. Data resources • The navigation equations • describe how the sensor outputs are processed in the on-board computer in order to calculate the position, velocity, and attitude. • contain instructions & data and are part of the airborne software. The data is stored in read-only (ROM) at the time of manufacturing • Mission-dependent data (e.g. waypoints) are either loaded from cockpit keyboard or a cartridge (data-entry device)

41. Acrft navigation system • The system utilizes three types of sensor information • Absolute position data from radio aids, radar checkpoints, and satellites • Dead-reckoning data, obtained from inertial, Doppler, or air-data sensors, as a mean of extrapolating present position • Line-of-sight directions to stars, which measure a combination of position & attitude errors • The navigation computer combines the sensor information to obtain an estimate of acft’s position, velocity, and attitude.

42. Heading attitude To cockpit display pointing sensor Attitude • Inertial air data • Doppler Dead-reckoning computations • Position • Velocity • Attitude Way points Most probable position computation Position Course computations Star line of sight Celestial equations • Positioning sensors • Radio(VOR, DME, Loran, Omega) • Satellite (GPS) • Radar To map display To weapon computers Positioning computations Position data Velocity Block diagram of an aircraft navigation system System Hierarchy Time to go Range, bearing to displays, FMS Steering signals to autopilot

43. Geometry of The Earth (1) • Apparent gravity field g = the vector sum of the gravitational and centrifugal fields G = Newtonian gravitational attraction of the earth = inertial angular velocity of the earth(15.04107 deg/hr g = apparent gravity field

44. Geometry of The Earth (2) • For navigational purposes, the earth’s surface can be represented by an ellipsoid of rotation around the Earth’s spin axis • The size & shape of the best-fitting ellipsoid is chosen to match the sea-level equipotential surface.

45. Geometry of The Earth (3) Fig 2.2 Median section of the earth, showing the reference ellipsoid & gravity field

46. Coordinate Frames (1) • The position, velocity and attitude of the aircraft must be expressed in a coordinate frame. Navigation coordinate frame

47. Coordinate Frames (2) • Earth-centered, Earth-fixed (ECEF): The basic coordinate frame for navigation near the Earth • Origin is at the mass center of earth • y1, y2 Lie in True equator • y2  Lies in the Greenwhich meridian • y3  Lies along the earth’s spin axis • Geodetic spherical coordinates: Spherical coordinates of the normal to the reference ellipsoid. • Z1  longitude • Z2  geodetic latitude • Z3  altitude h above the reference ellipsoid • This system is used in maps and mechanization of dead-reckoning and radio navigation systems.

48. Coordinate Frames (3) • Geodetic wander azimuth: Locally level to the reference ellipsoid • Z3 is vertical up • Z2 points at an angle , west of true north. • Z1 points at an angle , north of true east • Most commonly used in inertial navigation

49. Dead-Reckoning Computation (1) • DR is the technique of calculating position from measuring of velocity. • It is the means of navigation in the absence of position fixes and consists in calculating the position(the zi-coordinates) of a vehicle by extrapolating (integrating) estimated or measured ground speed. • Prior to GPS, DR computations were the heart of every automatic navigator.

50. Dead-Reckoning Computation (2) • In simplest form, neglecting wind: Where: east & north distances traveled during the measurement interval Ground speed True heading Angle between acft heading and true north