B737NG IRS

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B737NG Inertial Reference System

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B737NG IRS

  1. 1. B 737 NG Ground School. See the aircraft study guide at www.theorycentre.comThe information contained here is for training purposes only. It is of a general nature it isunamended and does not relate to any individual aircraft. The FCOM must be consulted forup to date information on any particular aircraft.
  2. 2. B737-800FLIGHT MANAGEMENT SYSTEMS. INERTIAL REFERENCE SYSTEM
  3. 3. Navigation systems include the flight management system (FMS); globalpositioning system (GPS); air data inertial reference system (ADIRS); radionavigation systems (ADF, DME, ILS, marker beacons, and VOR); transponder;and weather radar.
  4. 4. Inertial Reference System. ADIRU.
  5. 5. Air Data Inertial Reference System (ADIRS)The ADIRS produces flight data such as position, speed, altitude and attitude forthe flight displays, flight management computers, flight controls, engine controlsand all other systems requiring inertial and air data.The major components of the ADIRS are:Two air data inertial reference units (ADIRUs)
  6. 6. Air Data Inertial Reference System (ADIRS)The ADIRS produces flight data such as position, speed, altitude and attitude forthe flight displays, flight management computers, flight controls, engine controlsand all other systems requiring inertial and air data.The major components of the ADIRS are:Four air data modules (ADMs)
  7. 7. Air Data Inertial Reference System (ADIRS)The ADIRS produces flight data such as position, speed, altitude and attitude forthe flight displays, flight management computers, flight controls, engine controlsand all other systems requiring inertial and air data.The major components of the ADIRS are:One inertial system display unit (ISDU)One dual mode select unit (MSU)
  8. 8. Air Data Inertial Reference System (ADIRS)The ADIRS produces flight data such as position, speed, altitude and attitude forthe flight displays, flight management computers, flight controls, engine controlsand all other systems requiring inertial and air data.The major components of the ADIRS are:Six static portsThree pitot probesTwo alpha vanesOne total air temperature probe
  9. 9. Inertial system display unit (ISDU)Dual mode select unit (MSU)Aft Overhead panel.
  10. 10. VHF NAV Radio IRS Source select switchesand FMC source select switch.Forward Overhead panel.
  11. 11. There are two air data Inertial Reference Units.
  12. 12. The ADIRU has two systems in one box.The Air Data Computer (AD)Inertial Reference System (IRS)There are two air data Inertial Reference Units.
  13. 13. AIR DATA
  14. 14. AIR DATA4 Air Data Modules Convert Atmospheric data into Digital signals.
  15. 15. AIR DATA4 Air Data Modules Convert Atmospheric data into Digital signals.The ADM’s send digital information to the ADIRU.The ADIRU send that information to the DEU’s for the CDS and otheraircraft systems.
  16. 16. Inertial Reference System. 3x Accelerometers3 X RingLaser Gyros
  17. 17. RING LASER GYROA ring laser gyroscope (RLG) Uses two counter-propagating lightbeams to detect rotation.
  18. 18. YAW ROLLPITCH Accelerometers
  19. 19. The idea behind the ring laser gyroscope actually dates back to 1913, when aFrench physicist, Georges Sagnac, experimented with rays of light moving inopposite directions around a circular cavity on a turntable. Sagnac showed thatwhen he rotated the turntable, the light traveling with the rotation arrived at atarget slightly after the light traveling against the rotation. He believed he hadproven the existence of ether in space. In fact, he was demonstrating aproperty of light that came to be understood much better with the inventionof the laser in the 1950s.A laser (light amplification by stimulated emission of radiation) operates byexciting atoms in a plasma to release electromagnetic energy, or photons, in acavity. Each end of the cavity reflects the energy back and forth, and it forms astanding wave pattern. The wave frequency—its pattern of peaks andtroughs—is determined in part by the length of the cavity.“If you had a linear laser and the light bounced back and forth between twomirrors at either end, and if you [increased] the spacing between those twomirrors slightly, you would actually stretch the wavelength of the light in thecavity,“What causes the light to stretch? The fact that it had to go farther. Becausewhen it comes back, it has to come back exactly the same way it left,Sagnac’s counter-rotating beams of light are analogous to beams in a linearcavity. If the turntable rotates clockwise, the beam traveling clockwise hasfarther to go to catch its starting point; the path of the counterclockwise beamis shorter.
  20. 20. 2 opposing beams
  21. 21. Reflected from mirrors
  22. 22. Rotation moves mirrors close to Greenbeam and further from Blue beam
  23. 23. Receiver collects Green Beam beforeBlue. The light frequency is shifted.
  24. 24. In a ring laser gyroscope, the two counter-rotating beams arechannelled to a photo detector. If the vehicle is not rotating, thebeams remain in phase. If rotation is occurring about one axis, onebeam continuously changes phase with respect to the other. A diodetranslates that moving interference pattern into digital pulses, eachpulse representing an angle of rotation typically .0005 degree perpulse. The rate at which the pulses are produced is also a measure ofthe rate of rotation.
  25. 25. During alignment senses EARTH GRAVITY and EARTHS ROTATION ONLY
  26. 26. During alignment senses EARTH GRAVITY and EARTHS ROTATION ONLYIt can only calculate its own LATITUDE!It is NOT able to calculate LONGITUDE! Am I in Beijing 40⁰ N or Madrid 40⁰ NEarths rotational velocity gives position North or South of the equator.(Velocity at the poles (theoretically) Zero. At the equator around 900 milesand hour.
  27. 27. Compares last LONGITUDE stored in memory ( LastPosition) with manually entered Longitude.If there is more than 1° ErrorThe CDU Scratch pad Message <ENTER IRS POSITION.>Is asking for conformation of the manually enteredposition.
  28. 28. Senses EARTH ROTATION VELOCITY and calculates own LATTITUDE.Compares own Latitude with manually entered latitude.If more than 1° error CDU Scratch pad message <ENTER IRS POSITION>Again asking for confirmation that the manually entered position iscorrect.
  29. 29. The final check during alignment is the storedposition of the origin airport entered in the CDUand the IRS present position.
  30. 30. CDU MESSAGE “VERIFY POSITION” ONLY ON THE GROUND! Indicates ORIGIN AIRPORT POSITION entered in the CDU and IRS POSITION DIFFER by more than 4 nm.
  31. 31. Inertial Reference System (IRS) Mode SelectorOFF –• alignment is lost• all electrical power is removed from the system after a 30 second shutdown cycle.ALIGN –• rotating the selector from OFF to ALIGN initiates the alignment cycle• rotating the selector from NAV to ALIGN automatically updates alignment and zeroes groundspeed error.NAV (detent position) –• system enters the NAV mode after completion of the alignment cycle and entry of presentposition• in NAV mode, all IRS information is available to airplane systems for normal operations.ATT – provides only attitude and heading information:• attitude information is invalid (attitude flag in view) until ALIGN light is extinguished• heading information is invalid (heading flags in view) until the actual magnetic heading ismanually entered after the ALIGN light is extinguished
  32. 32. FAULT LightIlluminated (amber) – a system fault affecting the relatedIRS ATT and/or NAV modes has been detected.
  33. 33. ALIGN LightIlluminated (white) –• steady – the related IRS is operating in the ALIGN mode, the initial ATTmode, or the shutdown cycle• flashing – alignment cannot be completed due to IRS detection of:• significant difference between previous and entered positions or an unreasonablepresent position entry• no present position entry.Extinguished –• IRS not in ALIGN mode• with mode selector in NAV, alignment is complete, and all IRS information is available• with mode selector in ATT, attitude information is available.Heading information is available following entry of initial magnetic heading.
  34. 34. ON DC LightIlluminated (amber) –• the related IRS is operating on DC power from the switched hot batterybus (AC power not normal)• if on the ground, the ground–call horn in the nose wheel well sounds,providing an alert that a battery drain condition exists• momentary illumination is normal during alignment self–test.
  35. 35. DC FAIL LightIlluminated (amber) –• DC power for the related IRS is not normal• if the other lights are extinguished, the IRS is operating normally on AC power.
  36. 36. IRS AlignmentAn IRS must be aligned and initialized with airplane present position before it can enter thenavigation mode. The present position is normally entered through the FMC CDU. If thepresent position cannot be entered through the FMC CDU, it may be entered through the ISDUkeyboard. The airplane must remain stationary during alignment.
  37. 37. IRS AlignmentAn IRS must be aligned and initialized with airplane present position before it can enter thenavigation mode. The present position is normally entered through the FMC CDU. If thepresent position cannot be entered through the FMC CDU, it may be entered through the ISDUkeyboard. The airplane must remain stationary during alignment.Normal alignment between 78 degrees 15 minutes North or South is initiated by rotating theMSU switch from OFF to NAV. The IRS performs a short power test, during which the ON DClight illuminates. When the ON DC light extinguishes and the ALIGN light illuminates, thealignment process begins. Airplane present position should be entered at this time. Alignmenttime varies from five minutes at the equator to seventeen minutes at 78 degrees 15 minutesNorth or South latitude.
  38. 38. IRS AlignmentAn IRS must be aligned and initialized with airplane present position before it can enter thenavigation mode. The present position is normally entered through the FMC CDU. If thepresent position cannot be entered through the FMC CDU, it may be entered through the ISDUkeyboard. The airplane must remain stationary during alignment.Normal alignment between 78 degrees 15 minutes North or South is initiated by rotating theMSU switch from OFF to NAV. The IRS performs a short power test, during which the ON DClight illuminates. When the ON DC light extinguishes and the ALIGN light illuminates, thealignment process begins. Airplane present position should be entered at this time. Alignmenttime varies from five minutes at the equator to seventeen minutes at 78 degrees 15 minutesNorth or South latitude.Magnetic variation between 82 degrees north and 82 degrees south is stored in each IRSmemory. The data corresponding to the present position are combined with the true headingto determine magnetic heading.
  39. 39. IRS AlignmentAn IRS must be aligned and initialized with airplane present position before it can enter thenavigation mode. The present position is normally entered through the FMC CDU. If thepresent position cannot be entered through the FMC CDU, it may be entered through the ISDUkeyboard. The airplane must remain stationary during alignment.Normal alignment between 78 degrees 15 minutes North or South is initiated by rotating theMSU switch from OFF to NAV. The IRS performs a short power test, during which the ON DClight illuminates. When the ON DC light extinguishes and the ALIGN light illuminates, thealignment process begins. Airplane present position should be entered at this time. Alignmenttime varies from five minutes at the equator to seventeen minutes at 78 degrees 15 minutesNorth or South latitude.Magnetic variation between 82 degrees north and 82 degrees south is stored in each IRSmemory. The data corresponding to the present position are combined with the true headingto determine magnetic heading.If the latitude/longitude position is not within 4 NM of the origin airport, the CDUscratchpad message VERIFY POSITION is displayed. If the enteredlatitude/longitude position does not pass the IRS internal comparison tests, thescratchpad message ENTER IRS POSITION is displayed.
  40. 40. IRS AlignmentThe flashing ALIGN light alerts the crew that the position entered does not passone of the two internal comparison tests and should be checked for accuracy. If theentered position does not agree with the last stored position, the first internal testis failed, and the ALIGN light will flash. If the same position is re-entered, the IRSwill accept the position and continue the alignment process. A second internalposition test compares the entered latitude with the system-computed latitude. Ifthis test is failed, the ALIGN light will again flash. If two consecutive entries ofthe same position do not pass the second internal position test, the FAULT lightwill illuminate. If the test is passed, the IRS will proceed to complete thealignment process and enter NAV mode.During transit or through–flight stops with brief ground times, a thirty second fastrealignment and zeroing of ground speed error may be performed by selectingALIGN while the airplane is parked. Present position should be simultaneouslyupdated by manually entering latitude and longitude prior to selecting NAV.Note: If the airplane is moved during alignment or fast realignment, the IRSautomatically begins the full alignment process.
  41. 41. NORMAL POWER SUPPLYLeft ADIRU AC Standby bus. Right ADIRU AC transfer bus 2
  42. 42. DC BACKUP SUPPLYBoth ADIRU’s supplied from the switched hot battery bus
  43. 43. DC BACKUP SUPPLY Both ADIRU’s supplied from the switched hot battery busWith the Aircraft on the ground. The GROUND CREW CALL HORN INTHE NOSE WHEEL WELL will sound after a 20 second delay!IRU on DC only!
  44. 44. DC BACKUP SUPPLY Both ADIRU’s supplied from the switched hot battery busWith the Aircraft on the ground. The GROUND CREW CALL HORN INTHE NOSE WHEEL WELL will sound after a 20 second delay!IRU on DC only!Both AC and DC must be available when first switched ON. There is a power supply test before alignment can begin.
  45. 45. IRU OUTPUTS
  46. 46. IRS MESSAGES ARE DISPLAYED IN THE CDU SCRATCHPAD
  47. 47. The ADIRU works only in True Heading.It contains a DATA BASE OF MAGNETIC VARIATION FROM 82° N to 82° SMagnetic variation is added or subtracted from true using the database.The aircraft is limited to operations within 82° N to 82° S unlessequipped with a polar navigation suite.
  48. 48. For normal operation both IRS are in NAV mode. With the IRSTransfer switch in NORMAL the left IRS is used by the left FMCand is shared by both Flight Control computers.The right IRS is used by the right FMC which works insynchronisation with the left FMCThe captains attitude and Vertical speed come from the left IRS.The F/O’s come from the right.
  49. 49. For normal operation both IRS are in NAV mode. With the IRSTransfer switch in NORMAL the left IRS is used by the left FMCand is shared by both Flight Control computers.The right IRS is used by the right FMC which works insynchronisation with the left FMCShould either IRS fail, the IRS transfer switch is used to switch allassociated systems to the functioning IRS.
  50. 50. Data DisplaysTwo windows display data for the IRS selected with the system display selector• type of data displayed is normally determined by the display selector• keyboard entry of present position or magnetic heading overrides the selected display• last digit of each window is for a decimal place (tenths).
  51. 51. Display Selector (DSPL SEL)TEST (spring–loaded to TK/GS) –• all lights in data displays and on the mode selector unitmomentarily illuminate, followed by a 10 second self–test• use only during alignment.TK/GS –• left window displays true track (course)• right window displays present ground speed (knots).
  52. 52. Display Selector (DSPL SEL)PPOS –• left window displays present latitude• right window displays present longitude.WIND –• left window displays present inflight true wind direction• right window displays present inflight wind speed (knots).
  53. 53. Display Selector (DSPL SEL)HDG/STS –• left window displays present true heading• right window displays any applicable maintenance status codes
  54. 54. Display Selector (DSPL SEL)HDG/STS –• left window displays present true heading• right window displays any applicable maintenance status codes• during alignment, right window displays minutes remaining untilalignment is complete. For alignments greater than 15 minutes, thewindow displays 15 until the time remaining reaches 14 minutes. Thedisplay then counts down in one minute intervals.
  55. 55. KeyboardPush –• alpha keys:• data displays are controlled by the keyboard when the N, S, E, W (latitude/longitude)or H (heading) keys are pushed• pushing an alpha key arms the keyboard for numeric entries.• numeric keys:• permit manual entry of present position when ALIGN light is illuminated• permit manual entry of magnetic heading when either mode selector is in ATT.
  56. 56. System Display (SYS DSPL) SelectorL – selects left IRS for the data displays.R – selects right IRS for the data displays. Enter (ENT) Key Illuminated (white) – N, S, E, W, or H entries are being keyed. Push – keyed data is entered into IRS following completion of valid self–test for reasonableness.
  57. 57. Clear (CLR) KeyIlluminated (white) – an ENT attempt has failed (entry notaccepted by IRS).Push – clears data display of any data not yet entered oraccepted. If illuminated, cue lights extinguish.
  58. 58. If the FAULT light on the IRS mode selector unit illuminates, this indicates:a) A fault with the DC power supply has been detected.b) Manual entry of an invalid present position.c) IRS alignment for the respective IRS is lost.d) A system fault affecting IRS ATT or NAV modes is detected.
  59. 59. If the FAULT light on the IRS mode selector unit illuminates, this indicates:a) A fault with the DC power supply has been detected.b) Manual entry of an invalid present position.c) IRS alignment for the respective IRS is lost.d) A system fault affecting IRS ATT or NAV modes is detected. FAULT Light Illuminated (amber) – a system fault affecting the related IRS ATT and/or NAV modes has been detected.
  60. 60. If you move the IRS mode selector to ATT during flight you will havewhat information?
  61. 61. If you move the IRS mode selector to ATT during flight you will havewhat information? When selecting ATT there is a 2 second delay to prevent accidental selection!
  62. 62. If you move the IRS mode selector to ATT during flight you will havewhat information?
  63. 63. HOW is the Heading Manually entered?
  64. 64. There are two ways in which manual heading can be entered. 1. Is on the POS INIT pageOnly displayed when either ADIRU is in ATT mode.
  65. 65. 2. Is on the ISDU Select HDG/STS Select H for Heading.Then Enter Magnetic Heading.
  66. 66. The IRS alignment time is;a) 5 minutes at the equator increasing to 10 minutes at 70 degrees latitude.b) 17 minutes at any latitude.c) 10 minutes at the equator reducing to 5 minutes at 70 degrees latitude.d) 10 minutes at the equator increasing to 15 minutes at 70 degrees latitude.
  67. 67. The IRS alignment time is;a) 5 minutes at the equator increasing to 10 minutes at 70 degrees latitude.b) 17 minutes at any latitude.c) 10 minutes at the equator reducing to 5 minutes at 70 degrees latitude.d) 10 minutes at the equator increasing to 15 minutes at 70 degrees latitude.
  68. 68. The IRS alignment time is;a) 5 minutes at the equator increasing to 10 minutes at 70 degrees latitude.b) 17 minutes at any latitude.c) 10 minutes at the equator reducing to 5 minutes at 70 degrees latitude.d) 10 minutes at the equator increasing to 15 minutes at 70 degrees latitude.Normal alignment between 78 degrees 15 minutes North or Southis initiated by rotating the MSU switch from OFF to NAV. The IRSperforms a short power test, during which the ON DC lightilluminates. When the ON DC light extinguishes and the ALIGN lightilluminates, the alignment process begins. Airplane presentposition should be entered at this time. Alignment time varies fromfive minutes at the equator to seventeen minutes at 78 degrees 15minutes North or South latitude.
  69. 69. WHY does it take longer to ALIGN at HIGH LATITTUDES?The IRS alignment time is;a) 5 minutes at the equator increasing to 10 minutes at 70 degrees latitude.b) 17 minutes at any latitude.c) 10 minutes at the equator reducing to 5 minutes at 70 degrees latitude.d) 10 minutes at the equator increasing to 15 minutes at 70 degrees latitude.
  70. 70. WHY does it take longer to ALIGN at HIGH LATITTUDES? EARTHS ROTATIONAL VELOCITY IS SLOWER!The IRS alignment time is;a) 5 minutes at the equator increasing to 10 minutes at 70 degrees latitude.b) 17 minutes at any latitude.c) 10 minutes at the equator reducing to 5 minutes at 70 degrees latitude.d) 10 minutes at the equator increasing to 15 minutes at 70 degrees latitude.Normal alignment should complete within 10 minutes at mostairports.If there is time pressure remember to select HDG/STS on the IRSDisplay panel to see the remaining time for alignment.
  71. 71. The ON DC light on the left IRS mode selector unitcomes on. This indicates that the left IRS is poweredfrom which source?
  72. 72. The ON DC light on the left IRS mode selector unitcomes on. This indicates that the left IRS is poweredfrom which source? The left IRS is operating on DC power from the switched hot battery bus.
  73. 73. During transit or through flight with a brief ground time, afast realignment of the IRS will normally be completed inwhat time?
  74. 74. During transit or through flight with a brief ground time, afast realignment of the IRS will normally be completed inwhat time?
  75. 75. The right IRS is electrically powered from:a) AC transfer bus 1 or the switched hot battery bus for a maximum of 5 minutes.b) AC Transfer bus 2 or the switched hot battery bus for a maximum of 5 minutes.c) AC transfer bus 1 or the hot battery bus for a maximum of 5 minutes.d) AC transfer bus 2 or the hot battery bus for a maximum of 5 minutes.
  76. 76. The right IRS is electrically powered from:a) AC transfer bus 1 or the switched hot battery bus for a maximum of 5 minutes.b) AC Transfer bus 2 or the switched hot battery bus for a maximum of 5 minutes.c) AC transfer bus 1 or the hot battery bus for a maximum of 5 minutes.d) AC transfer bus 2 or the hot battery bus for a maximum of 5 minutes.
  77. 77. The right IRS is electrically powered from:a) AC transfer bus 1 or the switched hot battery bus for a maximum of 5 minutes.b) AC Transfer bus 2 or the switched hot battery bus for a maximum of 5 minutes.c) AC transfer bus 1 or the hot battery bus for a maximum of 5 minutes.d) AC transfer bus 2 or the hot battery bus for a maximum of 5 minutes.
  78. 78. DC BACKUP SUPPLYAircraft on the ground. What indications do you get for IRU on DC only?
  79. 79. DC BACKUP SUPPLYAircraft on the ground. What indications do you get for IRU on DC only? GROUND CREW CALL HORN IN THE NOSE WHEEL WELL!
  80. 80. WHERE ARE IRS MESSAGES DISPLAYED?
  81. 81. WHERE ARE IRS MESSAGES DISPLAYED? CDU Scratch pad
  82. 82. The FMC alerting message VERIFY POSITION indicates:a) The aircraft is off of the flight plan course.b) Entered position information is contradictory.c) IRS position information is INVALID.d) Left FCM disagrees with the right FMC
  83. 83. The FMC alerting message VERIFY POSITION indicates:a) The aircraft is off of the flight plan course.b) Entered position information is contradictory.c) IRS position information is INVALID.d) Left FCM disagrees with the right FMC ORIGIN AIRPORT POSITION entered in the CDU and IRS POSITION DIFFERENT by more than 4 nm.
  84. 84. The END of IRSNow Take the test at www.theorycentre.com

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