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### 1 -efis

1. 1. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 AFD 31202 AV2250 ELECTRONIC FLIGHT INSTRUMENTATION SYSTEM
2. 2. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 CHAPTER 1 FLIGHT INSTRUMENTATION
3. 3. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Table of Contents LEARNING OBJECTIVES INTRODUCTION Angle of Attack System Pitot Static System Central Air Data Computer (CADC) ALTITUDE INDICATOR SYSTEM Altimeter principle Encoding Altimeter Altitude Alerter AIRSPEED INDICATOR Airspeed Indicator principle Maximum Allowable Airspeed / Mach Indicator True Air Speed (TAS) / Static Air Temperature Indicator
4. 4. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Table of Contents (cont’d) VERTICAL SPEED INDICATOR Vertical Speed Indicator Principle Instantaneous Vertical Speed Indicator (IVSI) COMPASS SYSTEM Magnetic Compass Compass Errors Flux Gate Compass ATTITUDE DIRECTOR INDICATOR (ADI) TURN AND BANK INDICATOR HORIZONTAL SITUATION INDICATOR (HSI)
5. 5. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Learning Objectives Upon completion of this chapter, you will be able to: State the functions of the flight instrumentation. Explain the principle of Altitude instrument system, - Radio/Barometric encoding altimeter system - Altitude Alerter. Explain the principle of airspeed instrument system, - Airspeed Indicator - Maximum-allowable airspeed/ Mach indicator - TAS (true airspeed)/SAT (static air temperature) indicator. Explain the principle of vertical speed instrument system - Instantaneous Vertical Speed Indicator
6. 6. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Learning Objectives (cont’d) Explain the principle of compass instrument system. - Magnetic Compass - Flux Gate (Flux Detector) Compass. Explain the principle of Horizontal Situation Indicator.
7. 7. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Introduction There are two group of basic instruments commonly found in aircraft: – Navigation instruments – Provide information which enables the pilot to guide the aircraft accurately along a given course. – Flight instruments - Aiding the pilot in controlling the altitude, attitude, airspeed, and direction of the aircraft. Navigation instruments consist of: – The Automatic Direction Finder (ADF) – Very High Omni Range (VOR) – Instrument Landing System (ILS) – Distance Measuring Equipment (DME) – Weather Radar Flight instruments consist of: – The Barometric Altimeter (Alt) – Airspeed Indicator (ASI) – Turn-and-Slip Indicator / Turn Coordinator – Magnetic Compass – Artificial Horizon (AH) / Attitude Director Indicator (ADI) – Horizontal Situation Indicator (HSI)
8. 8. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Aircraft Instrument Panel
9. 9. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Angle-of-Attack System The angle-of-attack indicating system: – Detects the local angle of attack of the aircraft from a point on the side of the fuselage – Provide reference information for the control and actuation of other systems in the aircraft Signals from the angle-of-attack transmitter are used: – For continuous visual indication to pilot – provides electrical signals to the stall warning system which operate the stick shaker when the aircraft is approaching stall Electrical switches are actuated at the angle-of-attack indicator at various preset angles-of-attack. The angle-of-attack indicating system consists of: – An airstream direction detector / AOA transmitter – AOA indicator
10. 10. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Angle-of-Attack System (cont’d) AOA indicator AOA transmitter Airstream direction detector sensing element measures local airflow direction relative to the true angle-of-attack by determining the angular difference between local airflow and the fuselage reference plane. The sensing element operates in conjunction with a servo-driven balanced bridge circuit which converts probe positions into electrical signals.
11. 11. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The operation of the angle-of-attack sensing element is based on detection of differential pressure at a point where the airstream is flowing in a direction that is not parallel to the true angle-of-attack of the aircraft. – This differential pressure is caused by changes in airflow around the probe unit which extends through the skin of the aircraft into the airstream. The exposed end of the probe contains two parallel slots which detect the differential airflow pressure. Air from the slots is transmitted through two separate air passages to separate compartments in a paddle chamber. Angle-of-Attack System (cont’d)
12. 12. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Any differential pressure, caused by misalignment of the probe with respect to the direction of airflow, will cause the paddle to rotate. Angle-of-Attack System (cont’d)
13. 13. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The moving paddles will rotate the probe, through mechanical linkage, until the pressure differential is zero. – This occurs when the slots are symmetrical with the airstream direction. Two electrically separate potentiometer wipers, rotating with the probe, provide signals for remote indications. Probe position, or rotation, is converted into an electrical signal by potentiometers which are the transmitter component of a self- balancing bridge circuit. When the angle-of-attack of the aircraft is changed:- – The position of the transmitter potentiometer is altered. – An error voltage exists between the transmitter potentiometer and the receiver potentiometer indicator. Angle-of-Attack System (cont’d)
14. 14. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Current flows through a sensitive polarized relay to rotate a servomotor in the indicator. The servomotor drives a receiver/ potentiometer in the direction required to reduce the voltage and restore the circuit to an electrically balanced condition. The indicating pointer is attached to, and moves with, the receiver/potentiometer wiper arm to indicate on the dial the relative angle-of-attack. Angle-of-Attack System (cont’d)
15. 15. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Some of the Flight instruments that operate using Pitot and Static pressure are:- – Altimeter – Airspeed Indicator – Rate-of-Climb Indicator Static air pressure is the ambient air pressure around the airplane Pitot air pressure is the air pressure in the Pitot probe tube as a result of the forward motion of the airplane. ICAO standard atmosphere state that at Sea Level (0 ft):- – Press 29.92 in Hg / 1013.25 Mb / 14.7 psi – Temp 15°C Atmospheric pressure and temperature decreases as altitude increases. Pitot-Static System
16. 16. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Pitot pressure provides impact air pressure; – The pressure of the airstream against the aircraft as it flies through the air. – Is called dynamic pressure [(Q = ½ ρV²), Q - Dynamic Pressure, ρ (rho) - density of air, V – velocity of aircraft] The head is mounted : – On the outside of the aircraft in a forward direction parallel to the aircraft's line-of-flight. – In an area where the air is least likely to be turbulent, such as the leading edge of the wing or the nose section. Pitot-Static System (cont’d)
17. 17. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Figure above show a pressure head which sense pitot and static pressure. Baffle plate - to prevent moisture and debris from entering the pitot tube. Drain hole – remove moisture and located at the bottom of the unit. The pitot tube leads back to a chamber near the rear of the assembly. A riser, or upright tube, routes the air from this chamber through tubing in the aircraft to all the instrument that required it. Small openings on the top and bottom surfaces of the pressure head allows still (static) air to enter into the static air chamber. Pitot-Static System (cont’d)
18. 18. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 A riser tube in the static chamber provides a sample of this atmospheric pressure to all the indicator that required Heating element is located within the head to prevent the unit from becoming clogged due to icing conditions experienced during flight. The heater is controlled by means of a switch in the cockpit. An alternate method of deriving pitot and static pressure may be obtained from separate pitot tubes and static vents installed in different locations on the aircraft. – left and right static ports are paralleled together to compensate for any variation in static pressure due to erratic changes in the aircrafts attitude. Pitot-Static System must be tested for leaks upon installing equipment that requires connection to pitot or static lines. Pitot-Static System (cont’d)
19. 19. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The method of testing consists basically of: – Applying pressure and suction to the pressure heads and static vents respectively, – Using a leak tester and coupling adapters – Measuring the rate of leakage to within the prescribed tolerances for the system. Pitot-Static System (cont’d)
20. 20. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
21. 21. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 When performing leak test, pressure and suction should be applied and released slowly to avoid damage to the instruments. Should an electric flight instrumentation system be installed, standby altitude and airspeed instruments must be provided – It operated from the pitot-static source in the event a failure should occur in the ADC or aircraft electrical system. Pitot-Static System (cont’d)
22. 22. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Aircraft that operate at high speeds and high altitudes can have significant errors in the pitot-static system instruments if it uses a simple system. – An Air Data Computer (ADC) is used to operate: Airspeed indicator Altimeter VSI Any other systems that require this data The air data computer is placed in the system between the sensor ports and the instruments to automatically apply corrections in order to increase accuracy. Central Air Data Computer (CADC)
23. 23. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The air data computer has three inputs; – Pitot pressure from the pitot tube – Static pressure from the static ports – Total air temperature (TAT) from a special TAT probe TAT measurement is needed to: – correct the instrument indications for friction heating of the air at high speeds. – TAT probe also permits the calculation of SAT (static air temperature) which is used to apply corrections for non-standard temperatures for any flight altitude. The outputs of the air data computer is supplied to a number of aircraft systems. Central Air Data Computer (cont’d)
24. 24. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 High speed jet airplanes require a machmeter; this could be a separate instrument or included with the airspeed indicator. Aircraft with an air data computer usually have a digital display on the instrument panel which gives: – Calculated true airspeed – Total air temperature or static air temperature. TAT includes the heating effect of the friction at high speed whereas SAT is just ambient outside air temperature. Central Air Data Computer (cont’d) An air data computer provides more accurate readings on the pitot-static instruments for high performance aircraft
25. 25. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The temperature indications are especially important for turbine engines – They are affected by the temperature of the intake air. The air data computer system automatically compensates for both temperature effects and the compressibility of the air at higher Mach numbers. – This helps to ensure accurate instrument readings throughout a wide range of altitudes and airspeeds. The altitude outputs supplied by the CADC are corrected for instrument scale error and static defect correction is provided as a function of mach. Central Air Data Computer (cont’d)
26. 26. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 A typical CADC supplies the following outputs in accordance with ARINC specification 565: 1. An encoded digit pressure altitude output, in increments of 100 feet, for use by an ATC transponder for automatic altitude reporting. 2. A dual-synchro coarse and fine altitude output for driving an electric servo altimeter. 3. Altitude rate output for driving an electric vertical speed indicator. 4. Outputs for operating electric mach, true airspeed, and static air temperature indicators. 5. Altitude, airspeed, and mach hold functions for use by the flight director system in computing vertical guidance steering commands for driving the autopilot elevator servo. 6. A failure monitor signal to actuate a malfunction indicator flag in the systems receiving information from the CADC. Central Air Data Computer (cont’d)
27. 27. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The Kollsman model 621 is a typical example of a standard ARINC CADC unit presently being used on large corporate and commercial transport aircraft. The principle functional components of the Kollsman CADC consist of – two servo-operated diaphragm displacement transducers, – a mach follow-up servo, and – the associated servo amplifier/failure monitor cards. Central Air Data Computer (cont’d) Central air data computer
28. 28. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The altitude transducer servo drives: – Fine and coarse output synchros – An altitude digitizer encoder – An altitude scale error and function potentiometer used in computing mach. The altitude hold functions are also geared to this servo shaft. The airspeed transducer servo positions an airspeed scale error potentiometer and an airspeed function potentiometer, also used in computing mach. The airspeed function potentiometer provides the signal for the mach servo. The mach servo shaft positions the potentiometer which provides the static source error correction as a function of mach. – It also provides the drive for the mach hold and the mach output synchros. Central Air Data Computer (cont’d)
29. 29. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 A change in static pressure produces an error signal in the altitude transducer. In repositioning the transducer to null the error signal, there are components to be driven to provide the desired outputs such as: – The altitude potentiometer – Coarse and fine synchros – Two clutched synchros – The digitizer The potentiometer provides an output for the computation of mach to: – The altitude scale error, – Linear altitude, and – Altitude function potentiometers. Central Air Data Computer (cont’d)
30. 30. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Summed into the input network of the altitude servo is a static source error correction signal which is supplied by the mach servo. The airspeed transducer has a follow-up servo similar to the altitude servo. – This servo produces a shaft output linear with airspeed. The shaft positions the potentiometer, accepts the airspeed scale error correction and supplies an output to the linear airspeed potentiometer and the airspeed function potentiometer used in computing mach. – Also geared to this shaft is the airspeed hold clutch servo. Mach is computed by altitude and airspeed functions to provide the shaft position for the static source error correction signal, which is used in the correction of altitude. – Also geared to the mach shaft are the mach output synchro and the clutched synchro for mach hold. Central Air Data Computer (cont’d)
31. 31. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Altitude Indicator System Although there are many different types of Altimeters in service, all pneumatic altimeters operate on the principle of an aneroid capsule, which expands or contracts with changes in atmospheric pressure. As the aircraft altitude increases, the static source senses the decrease in atmospheric pressure and causes the aneroid to expand. – This movement of the aneroid actuates mechanical linkages which drive the pointer to the proper altitude scale reading on the indicator. A bi-metallic yoke surrounding the aneroid compensates for inaccuracies caused by variations in temperature. Altimeter Principles
32. 32. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The most common source of altimeter error is caused by the scale not correctly oriented to the standard pressure conditions. Since the atmospheric pressure continually changes in level flight, the Altimeter scale must be calibrated to the local barometric setting before the Altimeter will indicate the correct altitude of the aircraft above sea level. When the barometric correction knob on the face of the instrument is turned, the pointer and aneroid mechanism move to the new altimeter setting. Two other types of error are also common: – Hysteresis error – Static port alignment error Altimeter Principles (cont’d)
33. 33. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Hysteresis error is induced by sudden changes in altitude which results in a lag in altimeter response due to the elastic properties of the materials which comprise the instrument. – This error will eliminate itself after a new altitude has been maintained. Another source of error is caused by the change in alignment of the static port with regard to the relative wind. The magnitude of error caused by static port misalignment will vary with the aircraft's speed and angle-of-attack. An unpredictable erroneous indication will be caused by installation of a static port on the fuselage where a disturbed air pressure field exists. Altimeter Principles (cont’d)
34. 34. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
35. 35. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Typical pneumatic altimeter mechanism
36. 36. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The Kollsman RADBAR (RADio-BARometric) Electropneumatic Encoding Altimeter System is designed to provide both barometric and radar altitude information in a single instrument. RADBAR Encoding Altimeter System RADBAR altimeter system
37. 37. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The barometric section of the Altimeter: – Measures and displays static-defect-corrected pressure altitude – Encodes that altitude into a binary code output It is sent to the onboard radio beacon Transponder for automatic altitude reporting (when operating in Mode C). Synchro outputs of the baro-corrected altitude are provided for: – Altitude Alerter – Flight Management System – Long-Range Navigation System An altitude rate signal is provided to drive an electric Vertical Speed Indicator. RADBAR Encoding Altimeter System (cont’d)
38. 38. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The basic mechanism of the barometric section of the RADBAR indicator is: – a servo operated, – diaphragm displacement, – follow-up transducer. By sensing the diaphragm motion through an inductive pickoff, very accurate repeatable altitude measurements are made and presented on the altimeter counter-drum pointer display. RADBAR Encoding Altimeter System (cont’d) RADBAR altimeter
39. 39. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The pointer makes one revolution per 1,000 feet and graduations are at 20-foot increments. The counter reads altitude in thousands and hundreds of feet. The knob located in the lower right-hand corner of the RADBAR Altimeter permits setting of the local barometric pressure in both inches of mercury and millibars. Setting of the barometric scale knob does not affect the reported altitude information sent to the Transponder, but only the indicated altitude reading on the Altimeter. Reported altitude is always the altitude relative to standard barometric pressure at sea level (29.92 inches of mercury). RADBAR Encoding Altimeter System (cont’d)
40. 40. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Depressing the decision height (DH) knob on the top right-hand comer of the RADBAR indicator will cause the radio altitude display to readout the preset decision height. Depressing and rotating the knob allows the new DH to be set into the system. Whenever the DH knob is depressed to display the DH altitude, the visual and aural DH warning circuit is self-tested. A self-test button is also included to test both the barometric and radio altitude sections of the altimeter. Depressing the self-test button displaces the pointer approximately 300 feet, and causes the digital readout to display all “8s". Releasing the button initiates a test of the complete radio altimeter system. RADBAR Encoding Altimeter System (cont’d) Decision Height and Self-Test
41. 41. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The optical encoder in the barometric section of the altimeter uses light-emitting diodes as light sources and photo-Darlington transistors as light sensors. An encoding disk with nine concentric tracks of clear and opaque sections is positioned between the LEDs and photo sensors. As the disk is rotated by the altimeter aneroid mechanism, the light passing through the clear sections of the disks tracks the altitude changes. For every 100 feet of altitude, a new combination of light patterns reaches the sensors to produce the coded altitude information which is processed into a binary code output and sent to the Transponder. RADBAR Encoding Altimeter System (cont’d) Altitude Digitizer
42. 42. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
44. 44. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The localizer and glideslope signals are also converted to provide voice output warnings of excessive localizer and/or glideslope deviation from center on ILS approaches. In actual operation, when the aircraft is on the ground: – the radio altitude section will display zero feet, and – a placard will show the legend "RADIO ALT'. After take-off, the radio altitude display will indicate the height of the aircraft above the terrain up to 990 feet. The voice function remains silent during take-off unless a negative radio altitude rate is sensed. The illuminated placard, "RADIO ALT", will remain on up to an altitude of 2,500 feet above ground level (AGL) and then turn off. Radio Altitude Readout with Voice Terrain Advisory (cont’d)
45. 45. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 As the aircraft descends to the approach altitude, – the placard will illuminate at 2,500 feet AGL, and – the radio altitude converter synthesized voice output will announce "TERRAIN" at 2,000 feet AGL. Radio Altitude will be displayed in 100-foot increments down to 1,000 feet AGL. The "TERRAIN" announcement will be repeated at the 1,000-foot level, and shortly thereafter, the radio altitude numerical display will illuminate at 990 feet above the terrain and begin to count down in 10- foot increments. At 900 feet AGL, the VTA will announce "NINE HUNDRED"; At 800 feet AGL, the announcement "EIGHT HUNDRED" will be heard. The announcements will continue at each 100-foot interval (700, 600, 500, etc.) until touchdown. Radio Altitude Readout with Voice Terrain Advisory (cont’d)
46. 46. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 When the aircraft reaches the minimum decision height (DH), or the altitude at which the pilot must declare a missed approach (“go- around") and abort the landing if the runway is not yet visible: – the external DH warning light will illuminate, – the aural warning from the external tone generator will sound, and – the VTA announcement "MINIMUM" will be heard over the cockpit speaker. The system also provides voice advisories for reminding the pilot to extend the flaps and lower the landing gear. If the aircraft deviates below the glideslope less than one dot on the CDI or HSI, the announcement "GLIDESLOPE" will be heard at a nominal voice level at two second intervals. Should the aircraft deviate below the glideslope more than one dot, the announcement "GLIDESLOPE" will be heard at above nominal voice levels at one second intervals. Radio Altitude Readout with Voice Terrain Advisory (cont’d)
47. 47. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The altitude alerter is an optional instrument used to alert the pilot of an approach to, or departure from, a preset flight level by means of automatic audio and visual signals. The input signals required to operate the altitude alerter consist of: – a two-speed, baro-corrected, synchro altitude signal from a servoed altimeter – a 26-volt AC 400-Hz reference voltage from the aircraft electrical bus instrumentation transformer. Altitude Alerter Altitude alerter/preselector
48. 48. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The altitude alerter incorporates a five-digit display to indicate the preset flight level. – It can be adjusted by means of a knob located in the lower right- hand corner of the instrument. A three-digit counter displays thousands and hundreds of feet. – Fixed zeros are placed in the tens and units digits. An altitude alert light is located on the left side of the instrument to indicate approach to or departure from the preset flight level. In addition to altitude performance data, the alerter displays an "OFF" flag to indicate a loss of either the altitude valid signal from the altimeter or 26-volt AC power. The alerter also contains dual coarse and fine differential resolver synchros to provide an altitude preselect output for the flight control system. Altitude Alerter (cont’d)
49. 49. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Typical altimeter/alerter wiring diagram
50. 50. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 In actual operation, as the aircraft approaches within 1,000 feet of the preset flight level, – the altitude alert light comes on and an aural tone is momentarily heard (for approximately two seconds) through an external tone generator. The light, however, remains on until the aircraft crosses 300 feet of the preset altitude, at which time it extinguishes. Should the aircraft deviate from the preset altitude by more than plus or minus 300 feet, the aural tone and alert light will again be activated. The light will then remain on until the aircraft returns to within 300 feet of the preset altitude, or until the pilot selects a new altitude setting on the alerter indicator. Altitude Alerter (cont’d) Flight Test Procedures
51. 51. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Airspeed Indicator System The airspeed indicator is basically a differential pressure gage which measures and indicates the difference between pitot and static air pressures. The airspeed indicator consists primarily of a sensitive metallic diaphragm that responds to pitot- static pressure differential and multiplies this movement through mechanical linkages to indicate the aircraft's speed on the dial face in terms of knots or miles per hour. Airspeed Indicator Principles
52. 52. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The majority of airspeed indicators are marked to indicate speed limitations at a glance. – The never-exceed velocity is designated by a red radial line; – A yellow arc designates the cautionary range; – A white arc is used to indicate the range of permissible limits for flap extension. Airspeed Indicator Principles (cont’d)
53. 53. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Airspeed Indicator Principles (cont’d) VSO – stall speed / minimum steady flight in landing configuration (lower limit of white arc) VFE – max. flap-extended speed (upper limit of white arc) VS1 – stall speed in specified configuration (lower limit of green arc) VNO – max. structural cruising speed (top of green arc, bottom of yellow arc) VNE – never exceed speed (upper limit of yellow arc, marked in red) VLE – max. landing gear-extended speed.
54. 54. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Another type of airspeed indicator commonly used is the maximum- allowable airspeed indicator. – This indicator includes a maximum- allowable needle, which shows a decrease in maximum-allowable airspeed with an increase in altitude. The needle operates from an extra diaphragm, – It senses changes in altitude, to provide an indication of the maximum-allowable airspeed at any altitude. Airspeed Indicator Principles (cont’d) Maximum Allowable Airspeed Indicators
55. 55. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Machmeters: – installed onboard high-performance aircraft – indicate the ratio of aircraft speed to the speed of sound at the particular altitude and temperature existing at any time during flight A machmeter usually consists of: – a differential pressure capsule which senses pitot-static pressure – an aneroid capsule which senses static pressure.  The actions of these capsule are mechanically resolved to display mach numbers on the face of the instrument. Airspeed Indicator Principles (cont’d) Machmeters
56. 56. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
57. 57. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Combined airspeed/mach indicators: – usually provided where instrument space is at a premium – it is desirable to present this information on a combined indicator These instruments display indicated airspeed, mach, and limiting mach by means of differential pressure and aneroid diaphragms. The combined airspeed/mach indicator uses a single needle which indicates airspeed on a fixed scale and mach on a rotating scale. A knob, located on instrument is provided to set a movable index marker to reference a desired airspeed/mach setting. Airspeed Indicator Principles (cont’d) Combined Airspeed/Mach Indicators
58. 58. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The Kollsman maximum- allowable airspeed/mach indicator is intended for use in subsonic aircraft to provide: – airspeed – mach – maximum allowable airspeed indications in a single instrument Maximum-Allowable Airspeed/Mach Indicator
59. 59. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The indicator comprises: – two separate capsule mechanisms – a stationary airspeed dial – a moving mach sub-dial – a single airspeed pointer – a maximum-allowable airspeed indication – an index marker which can be rotated by means of a knob in the lower left-hand corner of the instrument Maximum-Allowable Airspeed/Mach Indicator (cont’d)
60. 60. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 A white pointer indicates: – Airspeed against a fixed subdial calibrated from 60 knots to 400 knots – Mach number against a moving mach subdial calibrated from 0.3 mach to 1.0 mach. Maximum-allowable airspeed is indicated on the dial by a yellow and red marker. Maximum-Allowable Airspeed/Mach Indicator (cont’d)
61. 61. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The index marker is basically a manually-set command bug that: – permits the pilot to select a desired approach speed – provides signal outputs to drive the fast/slow speed command needle on the attitude direction indicator The speed command output signals are determined by the difference between the airspeed pointer and index marker. The indicator also provides: – airspeed hold – mach hold – AC and DC airspeed – mach analog outputs for use in the flight control system Maximum-Allowable Airspeed/Mach Indicator (cont’d)
62. 62. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The Kollsman maximum allowable airspeed/mach indicator comprises primarily of two mechanically independent diaphragm- operated mechanisms; – one responding to the differential pressure between pitot and static pressures – the other to static pressure only The airspeed mechanism of the indicator is driven from a diaphragm capsule with pitot pressure introduced into its interior, – while the exterior of the diaphragm is subjected to the static pressure introduced into the instrument case. The capsule expands approximately linearly with the indicated airspeed. Maximum-Allowable Airspeed/Mach Indicator (cont’d) Functional Description
63. 63. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The motion of the centerpiece of the capsule is transmitted to a jeweled rocking shaft by a dual link and lever arrangement. One link is connected to a short lever on the rocking shaft, which is at nearly right angles to the link. – This lever is lengthened or shortened to provide the correct calibration of the pointer on the spread-out linear section of the dial up to 200 knots. At 190 knots, the second link comes into contact with its lever. The second lever is longer than the first, and at 190 knots, is more nearly in line with the link. – This angular relation between link and lever converts the diaphragm's linear motion into rotational movement, linear with the log of differential pressure. – This nonlinear portion of the dial above 190 knots is required in order to correctly indicate mach. Functional Description (cont’d)
64. 64. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Both links are slotted so each can over travel while the other is active. A hairspring on the rocking shaft provides tension on the active link at all times. The rocking shaft motion is amplified by a step-by-step gear pair to turn the jeweled pointer shaft. Damping of the airspeed pointer is accomplished by a capillary tube through which the pitot pressure is fed into the capsule. The indication is compensated for ambient temperature changes by selection of materials for the frame, linkage, and capsule. Static balance is achieved through an adjustable counterweight on the rocking shaft and a balanced pointer shaft. Functional Description (cont’d)
65. 65. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The mach subdial is driven from an evacuated diaphragm capsule through: – a link – lever – rocking shaft – gearup stage The capsule expansion is linear with pressure altitude, and when modified by link and lever, the subdial is rotated in proportion to the log of static pressure. In the manner of a circular slide rule, this causes the correct Mach number for any altitude to appear opposite the corresponding airspeed value. The airspeed pointer indicates both mach and airspeed over the range where the sub-dial is visible. Functional Description (cont’d)
66. 66. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Modern commercial aircraft instrument panels often have installed a true airspeed (TAS) indicator to supplement the information provided by the airspeed/mach indicator. True airspeed is indicated airspeed corrected for variations in pressure altitude and temperature. TAS is always greater than indicated airspeed (IAS), except in extremely low temperatures at low altitudes. TAS/SAT Indicator
67. 67. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 A typical pneumatic TAS indicator consists of: – an aneroid – differential pressure diaphragm – bulb temperature diaphragm A typical pneumatic TAS indicator responds to changes in – barometric pressure – impact pressure differential – free air temperature The actions of the diaphragms are mechanically resolved to show true airspeed in knots on the dial face of the indicator. TAS/SAT Indicator (cont’d) Pneumatic TAS Indicator
68. 68. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The Kollsman TAS/SAT indicator is an electric flight instrument that provides a digital incandescent display of both true airspeed and static air temperature (SAT): – from analog signals received from a TAS/SAT computer, or – from an independent airspeed network contained within the static defect correction module TAS/SAT Indicator (cont’d) Electric TAS/SAT System TAS/SAT indicator
69. 69. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 In poor weather, SAT indicates the potential for icing to occur. During takeoff, it affects the amount of thrust available from the engines and available lift due to air density. The outside air temperature input for SAT computation is derived from a fuselage-mounted total air temperature probe that contains a thermistor. The thermistor has a negative temperature coefficient, or in other words, its resistance increases upon sensing a decrease in outside air temperature. At 0oC, the resistance of the temperature sensing element in the probe is typically 500 ohms. Within the TAS/SAT computer, a matrix of trimming potentiometers, connected to pots on the altitude and airspeed servos, compute the function of mach. The combination of temperature and mach produces the required true airspeed output. Electric TAS/SAT System (cont’d)
70. 70. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Another circuit within the TAS/SAT computer uses the same temperature probe input signal to provide a static air temperature output. The TAS and SAT output signals from the computer are provided to the TAS/SAT indicator. The TAS output is also provided to the long-range navigation system or flight management system for computation of ground speed. The DC SAT voltage from the computer is applied to the indicator where a squaring operation is performed in order to linearize the SAT voltage with temperature. – The computer outputs the square root of SAT. Electric TAS/SAT System (cont’d)
71. 71. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Electric TAS/SAT System (cont’d) Kollsman TAS/SAT indicator functional block diagram
72. 72. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The 20-volt DC SAT reference signal is also squared, and then subtracted, to provide 0 volts at 0oC. The SAT voltage is then applied to a scaling amplifier and measured by an analog-to-digital (A/D) converter. The output results in a seven-segment digital display of plus or minus SAT in degrees centigrade. The DC TAS voltage from the computer is applied to the indicator where a scaling function is performed, and then applied to an A/D converter in conjunction with a 20-volt DC TAS reference signal. – This output results in a seven-segment digital display of TAS in knots. Electric TAS/SAT System (cont’d)
73. 73. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Vertical Speed Indicator System The pneumatic vertical speed indicator is a sensitive differential pressure instrument that measures and displays the rate at which an aircraft is ascending or descending in altitude. The VS indicator is connected to the static system and senses the rate of change in static air pressure. The rate of altitude change, as shown on the indicator dial, is – positive (clockwise rotation of the pointer) in a climb – negative (counterclockwise pointer rotation) in a dive In level flight, the pointer remains at zero. Vertical Speed Indicator (VSI) Principles
74. 74. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
75. 75. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The case of the instrument is airtight, except for a small connection through a restricted passage to the static line. Inside the sealed case is a diaphragm with connecting linkage and gearing to the indicator pointer. Both the diaphragm and the case receive atmospheric pressure from the static line. When the aircraft is on the ground or in level flight, the pressures inside the diaphragm and the instrument case remain the same and the pointer indicates zero vertical speed. When the aircraft climbs, the pressure inside the diaphragm decreases but, due to the metering action of the restricted passage, the case pressure will remain higher which causes the diaphragm to contract. Vertical Speed Indicator (VSI) Principles (cont’d)
76. 76. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The diaphragm movement actuates the mechanism, causing the pointer to indicate a rate of climb. In a descent, the pressure conditions are reversed. The diaphragm pressure becomes greater than the pressure in the instrument case. – This causes the diaphragm to expand which drives the pointer mechanism to indicate a rate of descent. When the aircraft levels off, the pressure in the instrument case becomes equalized with the pressure in the diaphragm causing the diaphragm to return to its neutral position and the pointer to return to zero. Vertical Speed Indicator (VSI) Principles (cont’d)
77. 77. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 When the aircraft is ascending or descending at a constant rate, a definite ratio is maintained between the diaphragm pressure and the case pressure through the calibrated restricted passage. Since it requires approximately six to nine seconds equalizing the two pressures, a definite lag persists before the proper vertical speed is indicated. Also, any abrupt changes in the aircraft's attitude may cause erroneous indications due to the sudden change of airflow over the static ports. Vertical Speed Indicator (VSI) Principles (cont’d)
78. 78. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The instantaneous vertical speed indicator is a more recent refinement of the conventional pneumatic VS indicator. The lVSI incorporates acceleration pumps to eliminate the limitations associated with the calibrated leak. For example, during an abrupt climb, vertical acceleration causes the pumps to supply extra air pressure into the diaphragm to stabilize the pressure differential without the usual time lag. During level flight and steady-state climbs and descents, the instrument operates on the same principle as a conventional vertical speed indicator. Instantaneous Vertical Speed Indicator (IVSI)
79. 79. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The aircraft magnetic direction indicator or compass is a completely independent instrument. – It does not require any electrical or tubing connections. – It contains a compass card with magnets that line up with the magnetic flux lines of the earth. The following basic parts of a magnetic compass: 1. A compass card or float which is mounted on jeweled bearings. It has numbers and direction markings so that the magnetic heading of the aircraft can be read from the instrument. 2. The case is filled with a light oil (usually refined kerosene) which dampens float motion and lubricates the bearings. Magnetic Compass Compass Systems
80. 80. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The parts of a liquid-filled aircraft magnetic compass
81. 81. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 3. A diaphragm or bellows accommodates thermal expansion and contraction of the fluid. 4. The compensator is two small moveable magnets used to adjust the compass for deviation error. 5. The lubber line is a marker against which readings are taken. Magnetic Compass (cont’d) The face of a liquid-type magnetic compass The indicated magnetic heading is 035o
82. 82. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The magnetic compass is subject to a number of errors which affect its operation. – These include variation, deviation, acceleration error, northerly turning error and oscillation error. Variation error is simply the fact that a magnetic compass will give indications based on the magnetic north pole and not the north geographic pole. The normal grid lines on an aeronautical chart are in true directions based on the geographic poles and the equator. The north magnetic pole is hundreds of miles from the north geographic pole. In most locations, there will be a difference between true and magnetic directions. Compass Errors
83. 83. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 13 North Magnetic Pole Geographic North Pole o Isogonic lines Agonic line 20 o 15 o 10 o 5 o o 0 5 o 10 o 15 o 20 o
84. 84. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 TN MN VAR 12 E o 48 60 o o Easterly Variation TNMN VAR 12 W o 72 60 o o Westerly Variation
85. 85. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Lines of variation are drawn on aeronautical charts
86. 86. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 In Figure above shown how the amount of variation is drawn on aeronautical charts for pilots to use. There are some locations where true and magnetic directions are the same. – This would be along the line called the agonic line. Everywhere else the pilot would consult the variation markings on the map and add or subtract the appropriate number of degrees to convert from true to magnetic headings. Acceleration error and north turning error are both a result of compass dip. Compass Errors (cont’d)
87. 87. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
88. 88. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The earth is round so that at high latitudes in the northern hemisphere, the compass card will tilt downward toward the north magnetic pole. – This compass dip causes both of these errors. If an airplane is flying east and it accelerates, the compass will momentarily indicate a turn to the north. If it decelerates, it will indicate a turn to the south. North turning error occurs when the aircraft is flying north or south. If a turn is made from a north heading, the compass will indicate a turn in the opposite direction momentarily and then it will lag behind the actual heading during the turn. Compass Errors (cont’d)
89. 89. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 6 N 33 30 25 21 15 12 Turn Errors Compass briefly gives indication of turn in the opposite direction Compass indicates turn in correct direction but at a faster rate than actually being turned Aircraft heading NORTH Aircraft heading SOUTH Magnetic Dip Magnetic Dip
90. 90. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Turns from south will cause the compass to lead the actual heading or indicate a higher than actual turning rate. Oscillation error is caused by the very delicate bearings in the compass. In rough air, the compass will oscillate back and forth 40o, 50o or more. The compass may never settle down as long as the turbulence persists. – This forces the pilot to have to estimate the actual compass reading. Deviation error is the most important one for maintenance technicians because they usually perform the checks and adjustments for deviation error. – This error is also called magnetic influence error since it is caused by magnetic influences within the aircraft. Compass Errors (cont’d)
91. 91. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 All aircraft have some steel parts that may have some permanent magnetism. Most aircraft also have electrical circuits that can produce electromagnetic fields. Both of these can affect the magnetic compass and cause errors. The compensator magnets in the compass are used to adjust this error to a minimum. This process is called swinging the compass. It should be performed whenever equipment is installed that could cause a change or when a problem with the compass accuracy is suspected. Compass Errors (cont’d)
92. 92. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Earth magnetic field distorted by aircraft
93. 93. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Swinging the compass-the basic procedure is: 1. Locate a compass rose on a ramp area which is accurate and can be used as a reference. A compass rose is a circle with magnetic directions indicated as shown in Figure on the right side. 2. Configure the aircraft for the checks by turning on electrical equipment and radios, running the engines and establishing a level attitude. Compass Errors (cont’d) A compass rose contains the markings and numbers needed for magnetic direction references
94. 94. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 3. Set the compensators to zero (there are two little screws labeled N-S and E-W) 4. Point the aircraft north on the compass rose and adjust the N-S screw to zero error or as close to zero error as possible. 5. Point the aircraft east and adjust the E-W screw to zero error or as close to zero error as possible. 6. Point the aircraft south and remove half the error. 7. Point the aircraft west and remove half the error. Compass Errors (cont’d) A compass rose contains the markings and numbers needed for magnetic direction references
95. 95. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The process so far has averaged the error for all headings. Now you are ready to record the error. 8. Point the aircraft on all headings every 30o, and record the compass heading for each. 9. Prepare a placard which lists the deviation error at least each 30o. Place it on or near the compass and make a logbook entry. Compass Errors (cont’d) A compass rose contains the markings and numbers needed for magnetic direction references
96. 96. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The compass correction card is used to record the deviation error for the aircraft's compass. An example is shown. Compass Errors (cont’d)
97. 97. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 A newer type of compass is called the vertical card compass. It operates like the other types of magnetic compass but the presentation on the face of the instrument is a full compass card which is easier to read. It sometimes eliminates the use of oil and employs eddy current damping. Compass Errors (cont’d) The vertical card compass displays a complete compass card and is easier to read than the older type
98. 98. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The full compass card presentation of the vertical card compass makes it easier to read. If the pilot wants to turn to a heading of 180o, the presentation makes it easier to determine if it is quicker to turn left or right to reach that heading. The compensator screws can be seen at the bottom of the vertical card compass. Compass Errors (cont’d) The vertical card compass displays a complete compass card and is easier to read than the older type
99. 99. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The flux gate compass is a special type of remote mounted compass – It is more stable than a standard magnetic compass – It usually eliminates the problems of acceleration and north turning errors. The sensor used with a flux gate compass system is called a flux valve or flux gate. – It is a wheel shaped device made of a ferrous material with three spokes and the rim cut into three equal parts. Flux Gate Compass The flux valve sensor
100. 100. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The excitation coil is in the center and the pick up coils or output coils are installed with one on each spoke of the flux valve core. The excitation coil is supplied with AC current with a frequency of 400 Hz. It is designed so that when the current flow in the excitation coil is at peak value, the core material is saturated. Flux Gate Compass (cont’d) The flux valve sensor
101. 101. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 When the current falls below peak value, the earth's magnetic flux lines cut across the pick up coils and produce an output signal in each one. The excitation coil in effect alternately blocks out the earth's magnetic field and then allows it to move across the output coils. – This produces an AC output signal from each of the three output coils. Flux Gate Compass (cont’d) The flux valve sensor
102. 102. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Since the angle of the earth's flux lines to the flux valve changes for each different heading, the relative values of the three output voltages will be different for each different heading. Flux Gate Compass (cont’d) The changing angle of the earth's flux lines
103. 103. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 An electronic component measures the three output signals and derives the magnetic heading of the aircraft. In order to give accurate readings, the flux gate sensor must normally be maintained in a level, horizontal position with respect to the Earth's surface. – This leveling can be accomplished in one of two ways. In the first type of flux gate sensor found on aircraft, the sensor is suspended by a pendulous mechanism so that it can remain level when the aircraft attitude is changed. – This type of flux gate has a housing filled with a light oil to dampen the motions of the moving parts. In the second type of flux gate compass system, the flux gate sensor is stabilized by a gyro system to keep it level. Flux Gate Compass (cont’d)
104. 104. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The output signals from a flux gate sensor are sent to an electronic unit which amplifies the signals and calculates magnetic heading. The output of this electronic unit is sent to cockpit indicators that require magnetic heading information and sometimes to navigational systems that require heading information. The two common cockpit instruments that receive signals from the flux gate system are the HSI and the RMI (radio magnetic indicator). The flux valve sensors of HSI and RMI are normally installed near the wing tips to keep them away from magnetic influences in the aircraft. The location of the vertical card magnetic compass is also shown in Figure below. Flux Gate Compass (cont’d)
105. 105. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The location of the various components of a flux valve compass system
106. 106. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The HSI and the RMI both have a compass card which indicates the magnetic heading of the aircraft. The heading information comes from a flux gate compass system. The compass cards on both instruments are driven by a remote mounted directional gyro. The DG receives signals from the flux gate compass that automatically reset it to the correct magnetic heading. The remote DG is slaved to the flux gate compass and the compass cards on the instruments are slaved to the remote DG. Flux Gate Compass (cont’d)
107. 107. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The face of an RMI is shown in Figure below. The compass card in this instrument indicates the magnetic heading of the aircraft as previously described. The RMI can be identified by the two pointers that have a common pivot point in the center of the instrument. – These pointers are connected to radio navigation systems so that they point toward the location of the ground transmitter. The selector switches allow each pointer to be connected to an ADF or VOR radio receiver. Flux Gate Compass (cont’d)
108. 108. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The radio magnetic indicator (RMI) has a compass card which indicates the magnetic heading of the aircraft
109. 109. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
110. 110. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The compass cards in the aircraft HSI and RMI instruments
111. 111. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 1. Must be installed to prevent influence by airplane vibrations or magnetic fields. 2. Maximum deviation in level flight is 10 degrees on any heading. 3. Magnetic non-stabilized may deviate more than 10 degrees due to electric heated windshield etc. if either a stabilized magnetic direction indicator or DG is installed. Deviation over 10 degrees requires a placard. Fares for Compass Systems FAR 23.1327 Magnetic Direction Indicator
112. 112. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 1. Placard must be installed on or near the MDI (compass). 2. Placard must list calibration for level flight with engines running. 3. Placard must state if calibration is for radios on or off. 4. Calibration increments must be 30 degrees maximum. 5. More than 10 degrees deviation for electric heated windshield etc. must be placarded. FARs for Compass Systems (cont’d) FAR 23.1547 Magnetic Direction Indicator Deviation Placard
113. 113. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Attitude Director Indicator The artificial horizon indicates the aircraft's orientation relative to the horizon. – The instrument is based on a gyro with a vertical axis. – This provides a reference to the vertical and a measurement for two aircraft attitudes; pitch and roll. A basic artificial horizon contains the gyro inside of the panel instrument. The gyro is mechanically connected to the brown disk (earth) and a blue disk (sky) representing the horizon. Held in a gimbal, the gyro remains vertical for both yaw and pitch. The vertical gyro is designed with a tendency to align with gravity An improvement over the artificial horizon is the Attitude Director Indicator, or ADI (Figure on the right side).
114. 114. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
115. 115. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 Primarily an artificial horizon, the ADI is the obvious place to put glide slope and localizer pointers. The ADI also contains the indicator for the radar altimeter and DME distance. A specialized version of the ADI, when combined with an HSI, is called a flight director and contains other indicators.
116. 116. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The Turn-and-Bank indicators in Figure on the right shows the correct execution of a bank and turn and indicates the lateral attitude of the aircraft in level flight. The turn needle is operated by an electric gyroscope. A gyroscope consists of a rotor mounted on moveable frames. Turn-and-Bank Indicator
117. 117. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 When the rotor spins at high speed, the spin axis on which it turns continues to point to the same direction, no matter how the frames are moved. The spin axis is automatically positioned parallel to the earth's axis. A gyro turns over slowly as the earth rotates. – This turning, called precession can cause the spin axis to change direction. The turn needle indicates the rate, in number of degrees per second, at which an aircraft is turning about its vertical axis. It also provides information on the amount of bank. Turn-and-Bank Indicator (cont’d)
118. 118. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 The gyro axis is horizontally mounted so that the gyro rotates up and away from the pilot. The gimbal around the gyro is pivoted fore and aft. Gyroscopic precession causes the rotor to tilt when the aircraft is turned. Due to the direction of rotation, the gyro assembly tilts in the opposite direction from which the aircraft is turning. – This prevents the rotor axis from becoming vertical to the earth's surface. The linkage between the gyro assembly and the turn needle, called the reversing mechanism, causes the needle to indicate the proper direction of turn. Turn-and-Bank Indicator (cont’d)
119. 119. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 A single needle-width deflection shows when the aircraft is turning at one and one half degrees per second or half standard rate (four minutes for a 360o turn). The slip indicator (ball) part of the instrument is a simple inclinometer consisting of a sealed, curved glass tube containing kerosene and a black agate or a common steel ball bearing, which is free to move inside the tube. The fluid provides a damping action, ensuring smooth and easy movement of the ball. The tube is curved so that in a horizontal position the ball tends to seek the lowest point. During coordinated turns and straight-and-level flight, the force of gravity causes the ball to rest in the lowest part of the tube, centered between the reference wires. Turn-and-Bank Indicator (cont’d)
120. 120. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
121. 121. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 It was developed to assist pilots to interpret and use aircraft navigational aids It displays information obtained from combinations of the heading indicator, radio magnetic indicator (RMI), Course Deviation Indicator (CDI). It may also display VOR, DME, ILS or ADF information. Aircraft heading is displayed on a rotating compass card under the heading lubber line. Course pointer provides magnetic bearing information from the aircraft to the selected ground station (VOR or ADF). Fixed aircraft symbol and course deviation bar display the aircraft's position relative to the selected course (VOR or ILS localizer). Compass card is positioned by the DG, which uses a synchro-based servo system in the same fashion as employed in the RMI. Some HSI also display Glideslope and Localiser. Horizontal Situation Indicator (HSI)
122. 122. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000
123. 123. FOR TRAINING PURPOSE ONLY Subject Code: AFD 31202 Malaysian Institute of Aviation Technology Issue No : 000 HSI display