5.15 Typical electronic digital aircraft systems
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  • 1. Module 5: Digital Techniques and Electronic Instrument Systems 5.15 Typical Electronic-Digital Aircraft Systems
  • 2. Overview  CMS & BITE: Computer Maintenance System & Built-In Test Equipment  ACARS: Aircraft Communication Addressing and Reporting System  EFIS: Electronic Flight Instrument System  EICAS & ECAM  FBW: Fly-By-Wire  FMS: Fly Management System  GPS: Global Positioning System  INS / IRS: Inertial Navigation System / Inertial Reference System  TCAS: Traffic Collision Avoidance System  DFDR / CVR: Digital Flight Data Recorder / Cockpit Voice Recorder
  • 3. On-Board Maintenance Facilities  CMU  BITE  ACMS
  • 4. On-board Maintenance Facilities  Data on the aircraft are acquired by:
  • 5. BITE  Built-in Test Equipment:  A system is composed of LRUs, which can be computers, sensors, probes, actuators etc. which perform specific functions.  A part of each system is dedicated to functions such as: monitoring, testing and troubleshooting.  This part of the system is the Built-in Test Equipment.  BITE can (a) perform error detection test (b) isolation: identify the possible failed LRUs and give a snapshot of the system when the failure occurred, (c) memorization: record the error in a memory device.  The information are sent to the Centralized Maintenance Computer.
  • 6. BITE Concept
  • 7. Testing with BITE  Several kinds of tests:  Power-up test:  Ensuring compliance with safety objectives.  It is performed only on ground, because they disturb normal operation.  They are performed after long power cuts (more than 200msec).  If the aircraft is airborne the test is limited to a few items to enable a quick return to operation of the system:  CPU test  memory test  ARINC test  I/O test  configuration test  However, when we normally refer to power-up tests, we assume the aircraft is on ground.
  • 8. Testing with BITE  Cyclic tests (also called operation test):  They are carried out permanently, because they do not disturb normal operation.  Examples: Watchdog test (i.e. CPU reset). RAM test.  System tests:  Tests available to the maintenance staff, for troubleshooting purposes.  Similar to ground power-up tests, but more complete.  Examples: Tests performed after the replacement of an LRU.  Specific tests:  Available only to specific systems.  They are performed to generate stimuli to other devices, such as actuators or valves.  They have major effect on aircraft (such as automatic moving of flaps etc.)  They are performed only on ground by maintenance staff.
  • 9. BITE Inside a Computer Make a power up test when the computer starts-up Operate normally and perform the cyclic tests. If we are on ground, provide the option to do system or specific tests. Otherwise, continue with normal operation.
  • 10. ACARS
  • 11. Aircraft Condition Monitoring System  Monitoring of engine, APU, performance monitoring and troubleshooting.  Collects, records and processes aircraft system data.  ACMS data can be forwarded to the MCDU, to a printer, transmitted through ACARS etc.
  • 12. ACMS architecture  It consists of two parts:  Data Management Unit (DMU): Handles and stores system data.  Flight Data Interface Unit (FDIU):  Provides DMU with data from the engines, systems etc. DMU (Data Management Unit)
  • 13. Electronic Library System  Collection and presentation of technical and operational material relating to aircraft, in a digital form.  Can be accessed by flight crews and maintenance staff through computers.  It’s a database of guides and manuals, stored in a computer and accessed by an LCD touch screen.  Usually, an ARINC 744A printer is connected to the library system, for document printing.  ARINC 744A is the standard airborne printer protocol.
  • 14. Aircraft Communication Addressing and Reporting System  ACARS:  An air-ground communication data linked network.  It is used to transmit or receive automatically or manually generated reports to or from the ground station.  ACARS protocol was designed by ARINC.  Communication can be transferred through ground VHF stations or SATCOM (Satellite Communication).
  • 15. Why ACARS?  Prior to ACARS development all communications between aircraft and ground were VHF or HF voice communications.  To reduce crew workload and ensure data integrity, developed ACARS communication system.
  • 16. VHF Usage  AM: KHz (Not used in aviation).  HF: 3 – 30MHz (Used in aviation for longer range, e.g. when flying above Antarctic).  VHF: Above 30MHz (Normally used in aviation).  Note: Higher frequencies are more easily absorbed by objects.
  • 17. Automatic ACARS messages  ACARS interface with FMS (Flight Management Systems) enables the automatic receiving of weather reports from the ground.  Major flight phases (OOOI):  Out of the gate, Off the ground, On the ground, and Into the gate messages.  Engine reports in real time can be automatically sent from the airplane to the airliners.  In case of failures during flight, real time information can be uploaded by the manufacturers associated with the fault.
  • 18. Non-automatic messages: Interaction between the crew and the ground.  Communication between the flight crew and the ground is made through FMS (it’s similar to email).  Messages examples:  Weather  Winds  Clearances  …  After Air France Flight 477 it has been discussed to make ACARS an online black-box, to retain flight information in case of lost black-box.
  • 19. How is an ACARS message propagates?  Through a VHF network:  Only applicable to land masses, where a VHF ground network is installed.  Used for up to 200miles transmission range.  Through an HF network:  Used in areas such as the poles and oceans.  Completed in 2001.  Through satellites:  Provides world-wide coverage.  The message passes through an ACARS network (through ARINC’s servers) to the operator’s center.  The operators center can be either CAA or a flight operator.  ACARS service providers are used to propagate the message to the destination.
  • 20. ACARS messages categories  2 types of messages:  Air Traffic Control: Messages from / to ATC. (e.g. clearance).  Aeronautical Operation Control: Messages from / to the base (flight operation department). (e.g. fuel consumption, engine performance etc.)  The message format is defined by a specific ARINC protocol.  Each message contains an address label.  Message Example: ACARS mode: H Aircraft reg: D-AIRL [A321-131] Message label: 1L [Off message] Block id: 9 Msg no: M23A Flight id: LH3394 Org: LH06LT [Munich, Germany-Athen, Greece] [Lufthansa] Flight distance: appr. 1511km Flight time: appr. 1.7 hours Message content: 00016234212AN((628D8UVPCR(GKTRRUBW
  • 21. ACARS vs. CPDLC  Controller–pilot data link communications  It is built on ACARS. The aim is to reduce voice congestion.  It’s another communication system between the flight crew and the flight controller.  Similarities with ACARS:  Uses VHF, HF and Satellite.  Text messages.  Differences with ACARS:  Designed only for communication between the flight crew and the controller.  However, in Boeing 777 CPDLC messages can be sent to the company, as well.
  • 22. The future of ACARS  ATN: Aeronautical Telecommunications Network  An integrated network inspired from the Internet architecture.  ACARS uses character messages, while ATN uses binary format.
  • 23. EFIS
  • 24. Electronic Flight Instrument System  EFIS:  PFD (Primary Flight Display)  ND (Navigation Display)
  • 25. EFIS Overview
  • 26. Airbus 320 Primary Flight Display Flight Mode Annunciator The flight mode annunciator (FMA), shows:  Autopilot operation  AP/FD vertical and lateral modes  Approach capabilities  AP, FD, A/THR engagement status.  Green color is “engaged”.  Blue color is “armed”. is related to approach indications in column 4.  Magenta are target speed, altitude etc.
  • 27. Flight Mode Annunciator
  • 28. Airspeed and Altitude Indications Speed after 10sec.
  • 29. PFD Errors and Messages
  • 30. Boeing 777 Primary Flight Display
  • 31. Boeing 777 Primary Flight Display
  • 32. Airbus 320 Navigation Display
  • 33. ND Warnings and Messages
  • 34. Boeing 777 Navigation Display
  • 35. Boeing 777 Navigation Display
  • 36. Boeing 777 Navigation Display
  • 37. Boeing 777 Navigation Display
  • 38. ECAM
  • 39. EIS Components  DMC: Digital Management Computer or Symbol Generator:  Generates data in a compatible format with the display units.  Contain CPUs, RAM, display drivers, raster generators etc. In case of failure of DMC1 or DMC2. System Data Acquisition concentrator
  • 40. EICAS Control Panels
  • 41. Crew Alerting System Examples
  • 42. Fly-By-Wire
  • 43. Fly-By-Wire  Fly-By-Wire (FBW) is a system that replaces the conventional manual flight controls of an aircraft with an electronic interface.  Flight control computers determine how to move the actuators at each control surface to provide the ordered response.  The movements of flight controls are converted to electronic signals transmitted by wires.  Fly-By-Wire allows automatic signals sent by the aircraft's computers to perform functions without the pilot's input, as in systems that automatically help stabilize the aircraft
  • 44. Conventional Flight Control Systems vs. Fly- By-Wire  Mechanical systems are heavy, non-accurate, prone to failures and errors. They have limited ability to compensate for changing aerodynamic conditions.  Fly-By-Wire implies a purely electrically signaled control system.  Computer configured controls: A computer system is interposed between the operator and the final actuator.  Fly-By-Wire examples:  Side-sticks  Control yokes  …
  • 45. Fly-By-Wire Philosophy  The mechanical system that controls the servomechanism, which moves the surface is replaced by a computer.
  • 46. Advantages of Fly-By-Wire  Due to the complex calculations that computers can make, they can make decisions without the pilot input. e.g. Automatic stability systems.  Safety:  More than one wires can be easily used to ensure the propagation of a signal.  More than one computers can be easily used, to ensure proper operation when one computer fails.  BITE  Weight Saving
  • 47. History of Fly-By-Wire  Tupolev ANT-20 in 1930:  The first airplane, where long runs of mechanical systems were replaced by electrical systems.  Concorde (1986):  Mechanical servo valves were replaced with electrically controlled servo valves, operated by an analogue electronic controller.  More sophisticated analogue computers were used in early versions of F-16.
  • 48. Digital Fly-By-Wire  In digital fly-by-wire flight control systems, the signal processing is done by digital computers and the pilot literally can "fly-via-computer".  The programming of the digital computers enables flight envelope protection.  Aircraft protection, reduced pilot’s workload.  FADEC: Full Authority Digital Engine Control  Permits control of flight surfaces and engine autothrottles to be fully integrated.
  • 49. FADEC advantages  FADEC contains a digital computer and a unit that controls the engine.  Allows maximum performance to be obtained from the engine.  Protection from dangerous situations such as low-speed stall or overstressing by flight envelope protection.  the flight control systems commands the engines to increase thrust without pilot intervention.  In economy cruise modes, the flight control systems adjust the throttles and fuel tank selections more precisely than all but the pilots.
  • 50. Further Fly-By-Wire developments  Fly-by-optics  Signal is transferred by light instead of current.  Power-by-wire  Having eliminated the mechanical transmission circuits in fly-by-wire flight control systems, the next step is to eliminate the bulky and heavy hydraulic circuits.  Fly-by-wireless  Intelligent Flight Control System  In case of a failure leading to a crash, computers make complex calculations to adjust the flight controls in a proper position to save the aircraft.  It is believed that enchantments are mostly software upgrades to the existing infrastructures.
  • 51. FMS
  • 52. Flight Management System: Introduction  FMS basic operation:  Compares the pilot selected flight plan with the actual horizontal and vertical aircraft position.  In case of difference between them, the FMS makes a steering and thrust command.  The FMS input and output device is the:  CDU: Control Display Unit or  MCDU: Multifunction Control Display Unit
  • 53. FMS operations  The pilot sets the flight plan through the MCDU.  A database with airports, runways, waypoints is used.  FMS automatically selects optimal parameters  e.g. climb ration, optimal speed etc.  Shows information about the flight plan on MCDU.  Exchanges information and commands the Autopilot / Autothrottle Flight System AFS.  Accepts DME and VOR inputs.  Gives information to the EFIS displays.
  • 54. FMS Description  Navigation:  FMS uses information form its database to automatically tune the navaids (ILS, VOR, DME).  Database must be updated every 28 days.  Performance:  The FMS calculates the shortest possible flying time at the lowest fuel consumption. Can give predictions of fuel quantities and arrival times at future points in the flight plan.  Guidance:  The FMS compares the desired position of the aircraft according to the flight plan, with the actual aircraft position. If there is a difference, FMS commands the AFS to bring the aircraft to the desired position.  Position and velocity are calculated using the IRS, GPS, VOR and DME.  EFIS Display:  FMS is the primary source of information displayed on EFIS.
  • 55. Setting up the FMS  INIT:  Set the take off runway and destination.  Set fuels.  Insert the waypoints.  F-PLN:  Check or modify the flight plan.  Eliminate discontinuities.  Performance:  Set flaps, weather and other information that affects performance for each flight phase.  Flight plan is displayed on ND.
  • 56. FMS block diagram  Flight Management Computer :  Performs the Navigation and performance calculations.  Stores the database and the selected flight plan.  Tunes to navaids.  Commands the AFS.  Makes EFIS display calculations
  • 57. Performance and in-flight displays
  • 58. GPS
  • 59. GNSS  GNSS (Global Navigation Satellite System) is an umbrella term for systems which are used to navigate and determine current position based on signals received from dedicated navigation satellites.  4 most important GNSS systems:  GPS  GEONASS  Galileo  Compass
  • 60. Principles of Operation  All satellite navigation systems use the same principle as DME (Distance Measuring Equipment):  The receivers measure the time it takes for a radio signal (around 1.5GHz) to travel from a transmitter in a satellite at a known point in space.  The receiver’s computer calculates the distance for more than one satellites.
  • 61. Satellites and Space Segment  There are 6 orbital planes with 4 satellites in each plane.  Each plane is inclined 55 degrees relative to the equator.  In the American GPS (NAVSTAR), there are 24 satellites at 11,000nm moving around the globe and return to the same position after 12 hours.
  • 62. Errors in Transmission  After the third measurement, one of the two possible points can be discarded, since it is far from the earth surface.  Possible errors that degrade the accuracy:  Atmospheric conditions  Noise due to sunspot activity.  Satellite clock drift: Variations of the clock of the satellite transmitter clock. (1nsec drift causes 1ft. distance error).  Calculations from a 4th satellite are needed to eliminate the effects of these errors.
  • 63. The European GPS System  A system of 30 satellites (under development).  Higher accuracy that the NAVSTAR (down to less than a meter). .
  • 64. Supplementary Systems needed for aircraft Navigation  Aircraft-based Augmentation Systems:  Sensors on the aircraft to detect the quality of the GNSS data received and correct them if necessary.  Satellite-based Augmentation Systems:  Geostationary satellites detect errors and correct GNSS signals transmitted to users.  They are limited to certain regions of the world.  WAAS (USA), EGNOS (Europe).  Ground-based Augmentation Systems:  Ground stations around the airports enhance positioning accuracy.  They are considered a long term replacement to ILS.  Example: Differential GPS: A ground-station propagates the GPS error to GPS receivers.
  • 65. INS / IRS
  • 66. Accelerometer  Acceleration moves the strings to the opposite direction of the movement.  The acceleration of indication can be integrated once to give velocity and once more to provide distance.  On the aircraft, induction is are used.  By knowing the starting position (IRS alignment) an aircraft can calculate the distance covered.
  • 67. The Gyroscope principle  When the rotor spins, no matter how the plane rotates on the yaw, the plane at which gyro rotates remains the same.  The gimbal will move so, the spin axis remain the same, no matter how it will rotate.
  • 68. Inertial Navigation System  Mechanical gyros:  A gyro along with an electrical system to measure the distance between the gyro spin axis and the gimbal movement.
  • 69. Inertial Reference System  Mechanical gyros are replaced with laser gyros, for greater accuracy.  Movement of gimbal is measured with the difference between arrival times of two laser beams.  When rotation takes place, the orientation of the mirrors changes, thus the beams reach at different times the detector.
  • 70. TCAS
  • 71. TCAS: Traffic Alert Collision Avoidance System  System designed to reduce the incidence of mid-air collisions between aircrafts.  When another aircraft appears in the vicinity an automatic negotiation is being made between the 2 aircrafts to avoid collision.  Information are displayed in EHSI (Electronic Horizontal Situation Indicator)  A number next to each aircraft shows the height of each aircraft in comparison to this one.
  • 72. TCAS Alerts  Traffic Advisory (TA):  Pilots are instructed to initiate a visual search for the traffic causing the TA.  If the traffic is visually acquired, pilots are instructed to maintain visual separation from the traffic.  Resolution Advisory (RA):  Pilots are expected to respond immediately to the RA.  This means that aircraft will at times have to maneuver contrary to ATC instructions or disregard ATC instructions.  Clear of Conflict (CC):  Pilots shall promptly return to the terms of the ATC instruction.
  • 73. TCAS Block Diagram
  • 74. TCAS Advisories Type Text Meaning Required action[1][2][5] TA Traffic; traffic. Intruder near both horizontally and vertically. Attempt visual contact, and be prepared to maneuver if an RA occurs. RA Climb; climb. Intruder will pass below Begin climbing at 1500–2000 ft/min RA Descend. Descend. Intruder will pass above. Begin descending at 1500–2000 ft/min RA Increase climb. Intruder will pass just below Climb at 2500 – 3000 ft/min. RA Increase descent. Intruder will pass just above. Descend at 2500 – 3000 ft/min. RA Reduce climb. Intruder is probably well below. Climb at a slower rate. RA Reduce descent. Intruder is probably well above. Descend at a slower rate. RA Climb; climb now. Intruder that was passing above, will now pass below. Change from a descent to a climb. RA Descend; descend now. Intruder that was passing below, will now pass above. Change from a climb to a descent. RA Maintain vertical speed; maintain. Intruder will be avoided if vertical rate is maintained. Maintain current vertical rate. RA Adjust vertical speed; adjust. Intruder considerably away, or weakening of initial RA. Begin to level off. RA Monitor vertical speed. Intruder ahead in level flight, above or below. Remain in level flight. RA Crossing. Passing through the intruder's level. Usually added to any other RA. Proceed according to the associated RA. CC Clear of conflict. Intruder is no longer a threat. Return promptly to previous ATC clearance.
  • 75. FDR & VDR
  • 76. Flight Data Recorder (FDR)  Flight Data Recorders store snapshots of the following information:  Altitude  Heading  Airspeed  Acceleration  Thrust on each engine  Use of Autopilot  Angle of attack  Air temperature  …  These information are from the same sources that supply the flight crew.  Recording begins with the start of the first engine and ceases at shut-down of the last engine.  Must survive impact velocity of 270knots.  Each snapshot is taken 1-2 times per second.  Can record from 17 – 25 hours continuously. Crash survivable memory unit. Underwater Locator Beacon (emitting for 30 days up to 20,000 ft.) Power Supply
  • 77. Cockpit Voice Recorder (CVR)  Often referred as “black box”.  Records all the communication transmitted or received by to / from the flight deck.  Voice communication between the flight crew.  All sounds in the cockpit, e.g. audio signals, sound alarms.  Must be capable of recording for at least 2 hours.  Recording begins with the start of the first engine and ceases at shut-down of the last engine.