Instrument Systems (ATA 31) B1 Past Paper PDF

Licence Category B1 Turbine Aeroplane Aerodynamics, Structures and Systems Module 11.5.1 Certification Statement and Objectives These Study Notes comply with the syllabus of JCARC \ EASA Regulation (EU) No. 1321/2014 Annex III (Part-66) Appendix I (as amended by Regulation (EU) No. 2018/1...

Licence Category B1 Turbine Aeroplane Aerodynamics, Structures and Systems Module 11.5.1 Certification Statement and Objectives These Study Notes comply with the syllabus of JCARC \ EASA Regulation (EU) No. 1321/2014 Annex III (Part-66) Appendix I (as amended by Regulation (EU) No. 2018/1142), and the associated Knowledge Levels as specified below: Knowledge Part-66 Levels Objective Ref. A B1 Instrument Systems (ATA 31) 11.5.1 1 2 Pitot static: altimeter, air speed indicator, vertical speed indicator; Gyroscopic: artificial horizon, attitude director, direction indicator, horizontal situation indicator, turn and slip indicator, turn coordinator; Compasses: direct reading, remote reading; Angle of attack indication, stall warning systems; Glass cockpit; Other aircraft system indication. Mideast Aviation Academy 5.1-2 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 ”THIS PAGE INTENTIONALLY LEFT BLANK” Mideast Aviation Academy 5.1-3 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Table of Contents Pitot-static systems 5 Glass cockpit (EFIS) 64 General 6 Introduction 64 Basic aircraft system 6 EFIS overview 66 Large aircraft system 8 Primary flight display (PFD) 66 Pitot-static systems on aircraft with EFIS 10 Multi-function display (MFD) 66 Altimeters 12 MEMS technology 68 Vertical speed indicator (VSI) 18 Attitude and heading reference system 68 Airspeed indicator (ASI) 22 Magnetometer 68 Speed definitions 26 Transponder 68 Mach meter 30 Other system variations 70 Reversionary modes and system failures 72 Gyroscopic instruments 32 Touchscreen EFIS 74 Gyroscopic principles 32 Applications of gyroscopes in aircraft 36 Other aircraft system indications 76 Heading indicator 42 Terrain awareness and warning systems (TAWS) 78 Attitude director indicator (ADI) 48 Ground proximity warning system 79 Attitude and heading reference system (AHRS) 50 Synthetic vision technology (SVT) 96 Turn and slip indicator/turn coordinator 52 Traffic awareness 98 Traffic collision avoidance system (TCAS) 100 Compasses 56 Vibration measurement and indication 106 Direct reading compass 56 Engine condition monitoring 110 Remote reading compass 56 Temperature measurement 112 Instrument layout 58 Flight data recorder (FDR) 116 Fuel quantity measurement and indication 122 Stall warning 60 Standby instruments 128 Angle of attack indicator 62 Flight management system (FMS) 130 Commercial aircraft EFIS 132 PFD and ND 134 EICAS and ECAM 150 ECAM (Airbus) and EICAS (Boeing) differences 176 Mideast Aviation Academy 5.1-4 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 ”THIS PAGE INTENTIONALLY LEFT BLANK” Mideast Aviation Academy 5.1-5 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Pitot-static systems General The flight environment data system comprises the pitot-static An altitude encoder (‘blind’ encoder) is also connected to the system and outside air temperature sensing. This determines static pressure line. This converts air pressure signals into a the following data from the atmosphere: digitally encoded altitude and is transmitted to the air traffic control secondary radar, and to other aircraft (for collision static pressure; avoidance) via the transponder. total (or Pitot) pressure; outside air temperature. Water can be drained from pitot-static lines by opening the drain plugs. Draining lines should only be required if the From this raw data, instruments or computers derive: airspeed indicator or altimeter appears erratic. altitude; Both the static ports and the pitot tube are electrically heated, vertical speed; controlled by a switch in the overhead control panel. airspeed; temperature. Basic aircraft system The Pitot tube for a small jet aircraft is connected directly to the airspeed indicator. The two flush static ports, one on either side of the fuselage, are connected and supply pressure to the airspeed indicator, altimeter, and vertical speed indicator. An alternate static air valve is connected into this line to supply static air to the instruments if the outside static ports should ever block with ice. The alternate air is taken directly from the cockpit. Mideast Aviation Academy 5.1-6 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Basic pitot-static system layout Mideast Aviation Academy 5.1-7 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Large aircraft systemould er types of large aircraft have a more complex, but still analogue, pitot-static system. Sometimes a third (auxiliary) pitot tube picks up ram air for the autopilot, overspeed warning system, and flight recorder. Duplicated interconnected pairs (left and right sides of the fuselage) static ports (or ‘vents’) are used. One pair of static port provides primary equalised ambient pressure to the airspeed and vertical speed indicators, and altimeter. The other pair of ports provide the co-pilot instruments. Alternate static ports can be used in the event of blockage by ice or debris of the main ports This is switched by the pilots. Newer types of aircraft, with a digital electronic flight Instrument system (EFIS), have an air data computer (ADC). Mideast Aviation Academy 5.1-8 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Static ports Dual pitot-static system layout Air data computer schematic, inputs and outputs Pitot tubes Mideast Aviation Academy 5.1-9 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Pitot-static systems on aircraft with EFIS A modern aircraft (all sizes) will have a digital cockpit, known as an EFIS installation. These aircraft have pitot tubes and static vents like their analogue counterparts, but the air pressures from the pitot tubes and static vents are connected to an air data computer (ADC) or air data module (ADM) which converts the pressure signals into digital electronic data, and computes the outputs of altitude, airspeed and vertical speed, for indication on the EFIS display units. Mideast Aviation Academy 5.1-10 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Air data computer has pitot and static pressure inputs, and electronic data outputs The primary flight display shows the data from the ADC Pitot static system with air data computer Mideast Aviation Academy 5.1-11 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Altimeters An altimeter is simply a barometer that measures the absolute The aneroid altimeter is calibrated to show the pressure directly pressure of the air. This pressure is caused by the weight of the as an altitude above mean sea level, in accordance with a air above the instrument and, naturally, this pressure constantly mathematical model defined by the International Standard changes. Also, as the aircraft climbs above the earth’s surface, Atmosphere (ISA). Older aircraft used a simple aneroid there is less air stacked on top of the aircraft and the absolute barometer where the needle made less than one revolution pressure decreases. By measuring this change of absolute around the face from zero to full scale. This design evolved to pressure, the aircraft’s altitude can be determined. the drum-type altimeter, where each revolution of a single needle accounted for 1,000 feet, and with thousand-foot The altimeter is one of the oldest flight instruments, and some increments recorded on a numerical odometer-type drum. To of the early balloon flights carried some form of primitive determine altitude, a pilot first had to read the drum to get the barometer which served to indicate the height. The standard thousands of feet, then look at the needle for the hundreds of altimeter used in many of the early aircraft has simple, feet. Modern aircraft use a ‘sensitive altimeter,’ which has a evacuated bellows whose expansion and contraction are primary needle, and one or more secondary needles that show measured by an arrangement of gears and levers that transmit the number of revolutions, similar to a clock face. In other the changes in dimensions into movement of the pointer around words, each needle points to a different digit of the current the dial. The dial is calibrated in feet, and a change in the altitude measurement. On a sensitive altimeter, the sea level barometric pressure changes the pointer position. reference pressure can be adjusted by a setting knob. The reference pressure, in inches of mercury in Canada and the US It is extremely important that the altitude indication is accurate, and hectopascals (previously millibars) elsewhere, is displayed and that the pilot is able to quickly read the altitude within a few in the small Kollsman window, on the face of the aircraft feet. These requirements are complicated by the fact that the altimeter. This is necessary since sea level reference pressure lapse rate, the decrease in pressure with altitude, is atmospheric pressure at a given location varies over time with not linear: that is, the pressure for every thousand feet is temperature and the movement of pressure systems in the greater in the lower altitudes than it is in the higher levels. The atmosphere. bellows are designed with corrugations that allow the expansion to be linear with a change in altitude. A knob on the outside of the instrument case rotates the scale and, through a gear arrangement, the mechanism inside the Principle of operation case. The barosetting is used for the correct altitude In aircraft, an aneroid barometer measures the atmospheric measurement. (QNH, QFE, QNE). pressure from a static port outside the aircraft. Air pressure decreases with an increase of altitude – approximately 100 hectopascals per 800 metres or one inch of mercury per 1,000 feet near sea level. Mideast Aviation Academy 5.1-12 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Principle of the aneroid capsule An altimeter face with Kollsman window showing the current barosetting An altimeter mechanism Mideast Aviation Academy 5.1-13 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Drum-type altimeters A sensitive pneumatic altimeter uses a stack of bellows, as As the aircraft climbs and air pressure falls, the capsules will seen below, to drive the pointers. If, for example, the bellows expand; similarly, as the aircraft descends, the static pressure change their dimensions one-quarter of an inch for the full will increase, and the capsules will contract. Since it is 35,000 feet, the tip of the long pointer will travel more than necessary to allow for different values of mean sea level 300 inches. This amplification requires a rather complex and pressure and also to allow the altimeter to be used for indicating delicate transmission and some very small gears. The friction altitude above the aerodrome, the altimeter is similarly provided inside the altimeter even under near-ideal conditions is such with a means of adjusting the level at which it will indicate zero that there must be the vibration of the instrument for an feet. This is done via a barometric subscale mechanism, which accurate reading. This is no problem in reciprocating engine adjusts the mechanical linkage and operates a set of digital aircraft, as there is enough vibration from the engine, but jet counters, or a calibrated dial. This is displayed in a window in aircraft often require instrument panel vibrators to keep the the face of the altimeter and is the datum pressure setting altimeter reading accurately. above which the instrument is now displaying altitude. The desired setting is again made using the knurled knob at the The sensitive altimeter bottom of the instrument. The sensitive altimeter employs a minimum of two aneroid capsules. This provides for a more accurate measurement of Types of altitude measurement pressure and also provides more power to drive the mechanical linkage. Pressure altitude Pressure altitude is the altitude above the standard datum The capsules are stacked together with one face fastened 1013.25 hPa or mBars (29.92 inches of mercury). down, which permits movement due to pressure changes at the other end. Density altitude Density altitude is pressure altitude corrected for temperature. The movement of the capsules in response to changes in Pressure and density are the same when conditions are altitude (pressure) is transmitted via a suitable mechanical standard. As the temperature rises above standard, the density linkage to three pointers that display (against a graduated of the air will decrease, and the density altitude will increase. instrument scale) the aircraft altitude in tens, hundreds and thousands of feet. The whole assembly is encased in a container, which is fed with static pressure but is otherwise completely airtight. Within the mechanical linkage, a bi-metallic insert is fitted to compensate for temperature changes that could affect the movement. Mideast Aviation Academy 5.1-14 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 A three-pointer altimeter An altimeter mechanism and display Location of altimeter on a Location of altimeter on a Single pointer/drum-type altimeter turboprop aircraft’s basic-T layout commercial aircraft’s primary flight display Mideast Aviation Academy 5.1-15 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 QNH (nautical height) setting An altimeter can measure height above almost any convenient If an aircraft flying at a constant 3,000 feet pressure altitude, for reference point, and for most flying, it measures the altitude example, may vary its height above the existing sea level above sea level. This is called indicated altitude and is read pressure, all of the aircraft flying in this same area will vary the directly from the indicator when the altimeter QNH setting is same amount and the separation between the aircraft will placed in the barometric window. remain the same. When an aircraft is flying with the altimeter set to indicate pressure altitude, it is operating at a flight level. Airport control towers give the pilot the altimeter setting which Flight level 320 is 32,000 feet, pressure altitude. is their local barometric pressure corrected to sea level. QFE (field elevation) setting When the pilot uses this barosetting, the altitude measurement When this baroscale is set, the altimeter shows an altitude of starts at sea level pressure. All elevations on aeronautical zero, with the aircraft on the ground. The baroscale shows the charts are measured from mean sea level (MSL), and therefore local air-pressure of the parking field. with a bit of simple arithmetic, the pilot can easily and accurately find the aircraft’s height above any charted position. If the pilot gets (via radio) the local baro pressure (QFE) of the When the aircraft is on the ground with the local altimeter airfield, during the approach the altimeter shows the height setting in the barometric window, the altimeter should indicate above ground. Touching the ground, the altimeter shows an the surveyed elevation of the aircraft’s parking space. altitude of zero. Indicated altitude gives us a measure of terrain clearance at This barosetting is seldom used and has been replaced by low altitudes. radio altimeters. STD (standard) or QNE (nautical elevation) setting Flight level, altitude, height and elevation For vertical separation between aircraft flying at higher altitudes, pressure altitude or flight level is used. When the Altitude − The altitude is the vertical distance between aircraft barometric pressure scale is adjusted to standard sea level and sea-level. pressure, 29.92 inches of mercury or 1013.2 mBar or hPa, the altimeter measures the height above this standard pressure The barosetting, therefore, is QNH. level. This is not an actual point but is a constantly changing Height − The height is the vertical distance between aircraft reference. The reason is that all aircraft in the upper level have and the terrain. their altimeters set to the same reference. The barosetting, therefore, is QFE. Mideast Aviation Academy 5.1-16 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Pressure measurement reference points Mideast Aviation Academy 5.1-17 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Vertical speed indicator (VSI) The rate-of-climb indicator is more properly called the vertical speed indicator. Its main function is that of helping the pilot establish a rate of ascent or descent that will allow them to reach a specified altitude at a given time. The vertical speed indicator has as its operating mechanism a bellows, or pressure capsule, similar to that of an altimeter, except that rather than being evacuated and sealed, it is vented to the inside of the instrument case through a diffuser which is an accurately calibrated leak. Principle of operation The principle of operation of one type of vertical speed indicator is as follows: When the aircraft begins to climb, the pressure inside the capsule begins to decrease to a value below that inside the instrument case, and the capsule compresses, causing the levers and gears to move the pointer so it will indicate a climb. The pressure inside the case now begins to decrease by leaking through the diffuser. This leak is calibrated so that there will always be a difference between the pressure inside the capsule and that inside the case that is proportional to the rate of change of the outside air pressure. As soon as the aircraft levels off, the pressure inside the case and that inside the capsule will equalise, and the indicator will show a zero rate of change. Mideast Aviation Academy 5.1-18 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 A VSI mechanism A VSI display Location of VSI on a turboprop Location of VSI on a aircraft’s basic-T layout commercial aircraft’s primary flight display Mideast Aviation Academy 5.1-19 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Instantaneous vertical speed indicator (IVSI) The instantaneous vertical speed indicator (IVSI) is also sometimes referred to as the inertial lead vertical speed indicator (ILVSI). The basic construction of this instrument is shown on the next page. It consists of the same basic elements as the conventional VSI, but it is additionally fitted with an accelerometer unit that is designed to create a more rapid differential pressure effect, specifically during the initiation of climb or descent. The accelerometer comprises of two small cylinders or dashpots, which contain inertial masses in the form of pistons that are held in balance by springs and their own mass. The cylinders are connected in the capillary tube system leading to the capsule and are thus open to the static pressure source. When the aircraft noses over to begin a descent, the inertia of the accelerometer piston causes it to move upward, instantaneously increasing the pressure inside the capsule and lowering the pressure inside the case. This change in pressure gives an immediate indication of a descent. At this time, the lag of the ordinary VSI has been overcome it begins to indicate the descent, there is no more inertia from the nose-down rotation, and the accelerometer piston will be centred so the instrument will be ready to indicate the levelling off from the descent. Mideast Aviation Academy 5.1-20 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Basic IVSI display Instantaneous vertical speed indicator mechanism Mideast Aviation Academy 5.1-21 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Airspeed indicator (ASI) The airspeed at which an aircraft is travelling through the air is Pitot pressure (PT) is taken into the capsule and the inside of essential to the pilot, both for the safe and efficient handling of the case is connected to the static pressure source (PS). the aircraft and as a basic input to the navigation calculations. The capsule expands in proportion to the difference between Principle of operation the pitot and the static pressure, and this expansion is When an aircraft is stationary on the ground it is subject to measured by a mechanical linkage is displayed as a pointer normal atmospheric or static pressure, which acts equally on moves over the dial which is graduated in miles per hour, knots all parts of the aircraft structure. In flight the aircraft experiences or kilometres per hour. an additional pressure due to the aircraft’s motion through the air, which is known as dynamic pressure, and is dependent The diagram below shows that the ram air pressure is the upon the forward motion of the aircraft and the density of the difference between total pressure and static pressure. If the air, according to the following formula: airspeed is zero, PT is equal to PS, so the ram air pressure is zero. PT = ½ρV2 + PS Where; PT = total or pitot pressure (also known as total head pressure or stagnation pressure) PS = static pressure ρ = air density V = velocity of the aircraft – true air speed (TAS) Rearranging the formula, the difference between the pitot and static pressures is equal to ½ρV2 (dynamic pressure). The airspeed indicator thus measures the pressure differential between the two sources and provides a display indication graduated in units of speed. An airspeed indicator is a differential pressure gauge that measures the difference between the pitot and the static pressure. It consists of an airtight case in which a thin metal capsule is mounted. Mideast Aviation Academy 5.1-22 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 The airspeed indicator and pitot/static pressure inputs ASI display with VNE ‘barber pole’ Mideast Aviation Academy 5.1-23 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Airspeed The principle of the stagnation point is used in the measurement of airspeed. Refer to the figure below. Air is directed from a pitot tube facing into the airflow to a flexible diaphragm in the airspeed indicator. This flexible diaphragm, in the form of a capsule, in fact, is a stagnation point and will feel the full effect of dynamic pressure. Static pressure is fed to both sides of the capsule so that it cancels out. The resultant movement of the diaphragm can be taken by a suitable linkage to a dial, this indicating airspeed. It should be noted that the airspeed indicator is, in fact, a dynamic pressure indicator but is calibrated suitably in knots. As it measures dynamic pressure directly it is extremely useful when flying the aircraft as most of the aerodynamic functions of the aircraft are directly related to dynamic pressure. For instance, the stalling speed of an aircraft is always measured in indicated airspeed and remains, for the same weight, pretty well a constant figure regardless of altitude. Mideast Aviation Academy 5.1-24 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 The airspeed indicator uses pitot pressure inside the capsule, and static pressure outside the capsule and thus measures dynamic pressure Mideast Aviation Academy 5.1-25 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Speed definitions Indicated airspeed (lAS) – The dynamic pressure of air True airspeed (TAS) – The equivalent airspeed against a vehicle, is equal to ½ ρV2, where ρ density, and corrected for density. V = true airspeed. An airspeed indicator calibrated to ISA mean sea level conditions records the dynamic pressure as a Density at sea level is the ISA sea level density of speed. If, for example, the indicated reading was 200 kts, then 1.225 kg/m3 or 0.00237 slugs/ft3. it means that the dynamic pressure is the same as it would be Note that the ratio is equal to 1 only at sea level, and at a true airspeed of 200 kts at standard conditions at mean sea level. reduces with altitude. Thus TAS increases with altitude if EAS is kept constant. Calibrated airspeed (CAS) – The indicated airspeed, corrected for instrument and position errors (IE and PE). At 40,000 feet, for example, the density ratio is This is sometimes called Computed airspeed, especially approximately 0.25. Since √ 0.25 = 0.5, the TAS is when air data computers are involved. twice the EAS. Memory aids Equivalent airspeed (EAS) – The calibrated airspeed corrected for compressibility (C). It should be noted that ICE-T (iced tea) or Indicated – Calibrated – Equivalent − True. compressibility is always a subtracted quantity. Pretty Cool Drink, giving the errors compensated for between Compressibility becomes significant at airspeeds above the speeds: Position – Compression − Density. 200 knots. It is the airspeed at sea level which represents the same dynamic pressure as that flying at the true airspeed (TAS) at altitude. It is useful for predicting aircraft handling, aerodynamic loads, stalling, etc. Note that instrument error and position error are sometimes neglected and thus EAS is then considered to be the same as IAS, and the two terms are used interchangeably. Mideast Aviation Academy 5.1-26 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Location of ASI on a turboprop aircraft’s basic-T layout An airspeed indicator showing: AS in knots (inner scale); MPH (outer scale); and TAS (knots – white scale) Location of ASI on a commercial aircraft’s primary flight display Mideast Aviation Academy 5.1-27 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Ground speed (GS) – can be determined by the vector Again, these technicalities are overlooked by the pilot who may sum of the aircraft’s true airspeed and the current wind refer to the airspeed as simply indicated airspeed. speed and direction; a headwind subtracts from the ground speed, while a tailwind adds to it. Winds at other Other speeds are indicated on the navigation display, namely angles to the heading will have components of either the true airspeed (TAS) and ground speed (GS). These speeds headwind or tailwind as well as a crosswind component. are useful for navigating the aircraft but not so useful for ‘flying’ the aircraft. An airspeed indicator indicates the aircraft’s speed relative to the air. The air may be moving over the The TAS and the GS are not usually indicated on small aircraft ground due to the wind, and therefore some additional due to the requirement to measure and calculate the air density means to provide position over the ground is required. in order to convert EAS into TAS. A comprehensive navigation This might be through navigation using landmarks, radio system is required to determine GS, a side result from this is aided position location, an inertial navigation system, or the ability to calculate and display wind-speed and wind- GPS. direction. Ground speed is quite different from airspeed. When an The figures below show a simple airspeed indicator as would aircraft is airborne the ground speed does not determine be used in a light aircraft, indicating only IAS, and a modern when the aircraft will stall, and it does not influence the EFIS system of a transport category aircraft, displaying IAS (on aircraft performance such as rate of climb. the PFD) and TAS/GS/wind-speed on the navigation display. Cockpit indications of airspeeds and ground speeds On a light aircraft, usually, only the IAS is shown in the cockpit. In reality, it is usually corrected for position error, so it should be called CAS, but this technicality is usually overlooked by the pilot who is unconcerned with such detail. On a large transport category aircraft, the indicated airspeed (IAS) is the primary indication, this being the airspeed which is of most significance to the pilot as it relates to the performance of the aircraft, especially the stall speed. Again, the IAS is in reality corrected for position error (CAS) and also compressibility (EAS), since the higher airspeeds of this type of aircraft make compressibility more significant. Mideast Aviation Academy 5.1-28 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 A basic airspeed An airspeed indicator with an Airspeed, windspeed and groundspeed relationship indicator, displaying additional outside air temperature IAS only input, displaying IAS (outer scale) when windspeed is head-on (or all headwind) and TAS (inner scale) Airspeed, windspeed and groundspeed relationship when windspeed is partially crosswind, using vector analysis to calculate ground speed A primary flight display (PFD) and navigation display (ND) showing the respective speed indications Mideast Aviation Academy 5.1-29 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Mach meter When aircraft fly at or near the speed of sound, a measurement The position of the ratio arm is therefore dependent on both is needed that compares the speed of the aircraft with the pitot excess and static pressure. Movement of the ratio arm speed of sound. This measurement is called the Mach number. controls the ranging arm. An indication of Mach 1 occurs when the aircraft is flying at the speed of sound. Below the speed of sound, the indication is This turns the pointer and displays the Mach number given as a decimal fraction, and above Mach 1, the indication corresponding to the ratio of pitot excess pressure and static is an integer with a decimal. For example, flight at Mach 1.25 is pressure. flight at an airspeed of 1.25 times the speed of sound at that altitude. Mach 0.75 is flight at an airspeed of 75% of the speed Any increase in altitude and/or airspeed will result in a higher of sound. Mach number. The speed of sound decreases at decreasing outside The critical Mach number is indicated by a specially shaped temperature (TAT). The Mach number increases if the aircraft lubber mark, which is located over the Mach meter dial. It is climbs with constant TAS. adjustable so that the critical Mach number for the particular type of aircraft may be displayed. A typical Mach meter, as shown below, consists of a sealed case containing two capsule assemblies placed at 90° to each other, and a series of mechanical linkages. The first capsule unit is an airspeed capsule and is connected to the pitot pressure pipeline, while the interior of the instrument case is fed with static pressure. The second capsule unit is an aneroid capsule, which responds to changes in static pressure. The airspeed capsule measures the difference between pitot and static pressure and expands or contracts in response to airspeed changes. The airspeed linkage transfers movement of the capsule to the main shaft and causes the shaft to rotate, thus moving a pivoted ratio arm in the direction A-B. The altitude (aneroid) capsule expands or contracts and responds to changes in altitude. Movement of the capsule is transferred to the ratio arm via a spring and pin, thus causing it to move in the direction C-D. Mideast Aviation Academy 5.1-30 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Analogue Mach meter Mach Meter principle Digital Mach information displayed on a primary flight display (PFD) Digital Mach display within an airspeed indicator Mideast Aviation Academy 5.1-31 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Gyroscopic instruments Gyroscopic principles A gyroscope is a spinning wheel or disc in which the axis of The behaviour of a gyroscope can be most easily appreciated rotation is free to assume any orientation by itself. When by consideration of the front wheel of a bicycle. If the wheel is rotating, the orientation of this axis is unaffected by tilting or leaned away from the vertical so that the top of the wheel rotation of the mounting, according to the conservation of moves to the left, the forward rim of the wheel also turns to the angular momentum. Because of this, gyroscopes are useful for left. In other words, rotation on one axis of the turning wheel measuring or maintaining orientation. produces rotation of the third axis. A gyroscope is mounted in two or three gimbals, which are A gyroscope flywheel will roll or resist about the output axis pivoted supports that allow the rotation of the wheel about a depending upon whether the output gimbals are of a free or single axis. A set of three gimbals, one mounted on the other fixed configuration. Examples of some free-output-gimbal with orthogonal pivot axes, may be used to allow a wheel devices would be the attitude reference gyroscopes used to mounted on the innermost gimbal to have an orientation sense or measure the pitch, roll and yaw attitude angles in a remaining independent of the orientation, in space, of its spacecraft or aircraft. support. In the case of a gyroscope with two gimbals, the outer gimbal, which is the gyroscope frame, is mounted so as to pivot about an axis in its own plane determined by the support. This outer gimbal possesses one degree of rotational freedom and its axis possesses none. The inner gimbal is mounted in the gyroscope frame (outer gimbal) so as to pivot about an axis in its own plane that is always perpendicular to the pivotal axis of the gyroscope frame (outer gimbal). This inner gimbal has two degrees of rotational freedom. The axle of the spinning wheel defines the spin axis. The rotor is constrained to spin about an axis, which is always perpendicular to the axis of the inner gimbal. So, the rotor possesses three degrees of rotational freedom and its axis possesses two. The wheel responds to a force applied to the input axis by a reaction force to the output axis. Mideast Aviation Academy 5.1-32 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Gyroscope and gimbals Toy gyroscope Mideast Aviation Academy 5.1-33 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Rigidity Whilst small, the rotor of a gyroscopic instrument must rotate at a very high rpm. Giving them inertia, also called rigidity and they maintain this alignment to a fixed point in space. This basically happens to every rotating object: wheel, propeller, etc. For example, this rigidity gives the moving bicycle its stability preventing it from falling over while riding it. A number of factors have their influence on rigidity: the mass of the rotor, its rpm or angular velocity and finally the distance of the mass to the axis of rotation. The larger the distance the greater the rigidity with equal rotational speed. Again, a bike has large wheels and can rotate slowly to obtain enough stability. Precession When you apply a force to a point around the spinning rim of the gyro, the rotor will tilt as if the force was 90° further in the direction of motion as shown in the image. This apparent displacement of the force is called precession. The amount of precession depends on the following factors: strength and direction of the force applied, the amount of inertia of the gyro (mass concentration on the rim), diameter and the rpm or rotational velocity of the gyro. Mideast Aviation Academy 5.1-34 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Force and resultant movement obstinacy – ‘precession’ Mideast Aviation Academy 5.1-35 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Applications of gyroscopes in aircraft General The gyro instruments include the heading indicator, attitude The direction indicator or makes it possible to fly accurate turns indicator and turn coordinator (or turn-and-slip indicator). The and headings but has their own distinctive features and turn coordinator is not always fitted on an aircraft. characteristics the pilot needs to be aware of. Each contains a gyro rotor driven by air or electricity and each The direction indicator, formerly called the directional gyro, and makes use of the gyroscopic principles to display the attitude also known as the heading indicator, uses the principle of of the aircraft. It is important that instrument pilots understand gyroscopic rigidity to provide a stable heading reference. the gyro instruments and the principles governing their operation. Turn coordinator The turn coordinator indicates the rate of turn of the aircraft. It Artificial horizon does not indicate the angle of bank. The attitude indicator is also known as the artificial horizon. The indicator needle is a miniature aircraft connected to a The purpose of the attitude indicator is to present the pilot with spring-loaded gimbal of the gyroscope inside the instrument. a continuous picture of the aircraft’s attitude in relation to the When the indicator needle is at full-scale deflection (as shown surface of the earth. The figure below shows the face of a below), the aircraft is turning at a rate of 360° per 2-minutes. typical attitude indicator. It should be noted that other attitude indicators differ in the details of presentation. The instrument also includes a slip indicator. This is a simple inertial device sensitive to sideways forces. In a ‘coordinated The small knob near the bottom of the instrument is used for turn’ there should be no sideways forces, so the slip indicator vertical adjustment of the miniature aircraft. During straight- should show in the centre. and-level flight, the miniature aircraft should be adjusted so that it is superimposed on the horizon line. Older aircraft may have a turn and slip indicator in place of the turn coordinator. This has a slightly different presentation but Direction indicator indicates essentially the same information as the turn The magnetic compass is the primary direction indicator in an coordinator. aircraft, but it is prone to a number of errors due to acceleration, turbulence and they are sometimes difficult to read. To solve this problem, we use a direction indicator based on a gyro. These are stable, accurate, easy to read and can be coupled to an autopilot and even synchronised to a magnetic compass. Mideast Aviation Academy 5.1-36 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Vertical and horizontal gyros Mideast Aviation Academy 5.1-37 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Artificial horizon The attitude indicator is also known as the artificial horizon. Once the artificial horizon line is aligned with the natural horizon of the earth during initial erection, the artificial horizon is kept The purpose of the attitude indicator is to present the pilot with horizontal by the gyro on which it is mounted. An erection a continuous picture of the aircraft’s attitude in relation to the mechanism automatically rights the gyro when precession surface of the earth. The figure below shows the face of a occurs clue to manoeuvres or friction. When the older-type gyro typical attitude indicator. It should be noted that other attitude tumbles because of extreme attitude changes, the rotor indicators differ in the details of presentation. normally precesses slowly back to the horizontal plane. Pitch attitudes are depicted by the miniature aircraft’s relative Even an attitude indicator in perfect condition can give slight movement up or down in relation to the horizon bat, also called erroneous readings. Small errors due to acceleration and the gyro or attitude horizon. Usually, at least four-pitch deceleration are not significant because the erection device reference lines are incorporated into the instrument. Two are corrects them promptly; nonetheless, the pilot should be aware below the artificial horizon bar and two are above. of them. Large errors may be caused by wear, dirty gimbal rings, or out-of-balance parts. Warning flags (see Attitude The bank indicator, normally located at the top of the Indicator figure, above right) may mean either that the instrument, shows the degree of bank during turns using index instrument is not receiving adequate electrical power or that marks. These are spaced at 10° intervals through 30°, with there is a problem with the gyro. larger marks; placed at 30°, 60° and 90° bank positions. The nose of the aircraft is depicted by a small white dot located between the fixed set of wings or by the point of the triangle as in the figure (see the bottom centre of the attitude indicator figure, below right). The sky is represented by a light blue and the earth is shown by black or brown shading. Converging lines give the instrument a three-dimensional effect. The small knob near the bottom of the instrument is used for vertical adjustment of the miniature aircraft. During straight- and-level flight, the miniature aircraft should be adjusted so that it is superimposed on the horizon line. Mideast Aviation Academy 5.1-38 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Mechanical attitude indicator Electronic attitude indicator on the instrument panel of a Cessna Citation Electronic attitude indicator using an LCD screen Mideast Aviation Academy 5.1-39 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Operation The attitude indicator uses a vertical gyro. The vertical gyro senses the relationship between the pitch and roll axes of the aircraft and a vertical line through the centre of the earth, and it gives a stable reference, so the actual pitch and bank angle are known to keep the wings level. The vertical gyro has two degrees of freedom. The axle of the wheel is always vertical. Vertical gyros are located inside horizon indicators or they are built into separate units as ‘remote’ vertical gyros. Their roll and pitch signals are used for artificial horizons, autopilots, flight directors and the weather radar antenna stabilisation. Mideast Aviation Academy 5.1-40 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 A vertical gyro used to sense aircraft pitch Attitude indicator mechanism A vertical gyro used as an indicator of pitch and roll (attitude indicator) Mideast Aviation Academy 5.1-41 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Heading indicator The heading indicator, formerly called the directional gyro, uses the principle of gyroscopic rigidity to provide a stable heading reference. The pilot should remember that real precession, caused by manoeuvres and internal instrument errors, as well as apparent precession caused by aircraft movement and earth rotation, may cause the heading indicator to ‘drift’. In newer heading indicators, the vertical card or dial on the instrument face appears to revolve as the aircraft turns. The heading is displayed at the top of the dial by the nose of the miniature aircraft. Another type of direction indicator shows the heading on a ring like the card in a magnetic compass. Because the heading indicator has no direction-seeking qualities of its own, it must be set to agree with the magnetic compass. This should be done only on the ground or in straight- and-level, unaccelerated flight when magnetic compass indications are steady and reliable. The pilot should set the heading indicator by turning the heading indicator reset knob at the bottom of the instrument to set the compass card to the correct magnetic heading. On large aircraft, this function is done using a compass controller. The pilot of a light aircraft should check the heading indicator against the magnetic compass at least every 15 minutes to assure accuracy. Because the magnetic compass is subject to certain errors, the pilot should ensure that these errors are not transferred to the heading indicator. Mideast Aviation Academy 5.1-42 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Mechanical direction indicator Electronic heading indicator on the instrument panel of a Bell 407 Electronic direction indicator using an LCD screen Mideast Aviation Academy 5.1-43 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Operation The heading indicator works using a gyroscope. The heading indicator is arranged such that the gyro axis is used to drive the display, which consists of a circular compass card calibrated in degrees. The gyroscope is spun either electrically or using filtered air flow from a suction pump (sometimes a pressure pump in high altitude aircraft) driven from the aircraft’s engine. Early directional gyros resembled the magnetic compass with its gyro rotor suspended in a double gimbal with its spin axis in a horizontal plane inside the calibrated scale. The caging knob in the front of the instrument could be turned to rotate the entyre mechanism and bring the desired heading opposite the reference mark, or lubber line. The rotor remains rigid in space, as the aircraft turned about the gyro. Vertical card directional gyro The vertical card compass has instead of a simple lubber line in front of the card, a symbol of an aircraft on its face, in front of the dial, with its nose pointing straight up, representing straight ahead. The circular dial is connected to the gyro mechanism, so it remains rigid in space and, as the aircraft turns about it, the dial rotates. The knob in the lower left-hand corner of the instrument may be pushed in and rotated, so the pilot can turn the mechanism to get the dial under the nose of the symbolic aircraft that corresponds to the heading shown on the magnetic compass. Mideast Aviation Academy 5.1-44 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 An old-style directional gyro A directional gyro’s operation on the aircraft Directional gyro mechanism Mideast Aviation Academy 5.1-45 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Horizontal situation indicator (HSI) The horizontal situation indicator (commonly called the HSI) is an aircraft flight instrument normally mounted below the artificial horizon in place of a conventional heading indicator. It combines a heading indicator with a VHF omnidirectional range-instrument landing system (VOR-ILS) display. This reduces pilot workload by lessening the number of elements in the pilot’s instrument scan to the six basic flight instruments. On the HSI, the aircraft is represented by a schematic figure in the centre of the instrument – the VOR-ILS display is shown in relation to this figure. The heading indicator usually slaves to a remote compass and the HSI is frequently interconnected with an autopilot capable of following the heading select bug and of executing an ILS approach by following the localiser and glide slope. On a conventional VOR indicator, left–right and to–from must be interpreted in the context of the selected course. When an HSI is tuned to a VOR station, left and right always mean left and right and “TO/FROM” is indicated by a simple triangular arrowhead pointing to the VOR. If the arrowhead points to the same side as the course selector arrow, it means “TO”, and if it points behind to the side opposite the course selector, it means “FROM”. The HSI illustrated below is a type designed for smaller aircraft and is the size of a standard 3 ¼-inch instrument. Airline and jet aircraft HSIs are larger and may include more display elements. The most modern HSI displays are solid state LCD displays (known as electronic horizontal situation indicator – EHSI) and often integrated with electronic flight instrument systems (EFIS). Mideast Aviation Academy 5.1-46 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 HSI EHSI Mideast Aviation Academy 5.1-47 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Attitude director indicator (ADI) When an attitude director (artificial horizon) also incorporates command bars (operated by the flight director), the instrument is known as an attitude director indicator (ADI). The most modern ADI displays are solid state LCD displays (known as electronic attitude director indicator – EADI) and often integrated with electronic flight instrument systems (EFIS). Mideast Aviation Academy 5.1-48 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 ADI EADI Mideast Aviation Academy 5.1-49 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Attitude and heading reference system (AHRS) An attitude and heading reference system (AHRS) consists of sensors on three axes that provide attitude information for aircraft, including roll, pitch and yaw. They are designed to replace traditional mechanical gyroscopic flight instruments and provide superior reliability and accuracy. The information provided by the AHRS is sent to the attitude and heading sections of an electronic flight instrument system (EFIS). AHRS have proven themselves to be highly reliable and are in common use in modern aircraft. AHRS are typically integrated with electronic flight instrument systems (EFIS) which are the central part of so-called glass cockpits, to form the primary flight display. AHRS can be combined with air data computers to form an air data, attitude and heading reference system (ADAHRS), which provide additional information such as airspeed, altitude and outside air temperature. The AHRS is not, by itself, able to provide a reference to the Earth’s magnetic field. For this capability, it must be connected to a magnetometer. Mideast Aviation Academy 5.1-50 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Typical AHRS sensor diagram The primary flight display (PFD) shows the data from the AHRS AHRS with magnetometer AHRS using MEMS technology Mideast Aviation Academy 5.1-51 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Turn and slip indicator/turn coordinator Turn and slip indicator These are actually two instruments in one housing. The simpler This tilt is opposed by both a dashpot which smooths out the instrument is an inclinometer set into the dial. This is a curved force and by a calibrated spring which restricts the amount the glass tube filled with a damping liquid, and riding in it is a black gimbal can tilt. A pointer is driven by the gimbal in such a way glass ball. When the aircraft is perfectly level and there are no that it indicates not only the direction of yaw but the amount of other forces acting on it, the ball will rest in the bottom centre its deflection is proportional to the rate of yaw. of the tube between two marks. In flight, the ball indicates the relationship between the pull of gravity G and centrifugal force Z caused by a turn. The pull of gravity is affected by the bank angle: the steeper the bank, the more the ball wants to roll toward the inside of the turn toward the low wing. Centrifugal force, on the other hand, pulls the ball toward the outside of the turn. The greater the rate of turn, the greater the centrifugal force. A coordinated or balanced turn is one in which the bank angle is correct for the rate of turn, and the ball remains centred. The gyroscopic part of the turn and slip indicator is a rotor, spun either by air or by an electric motor. This rotor has its spin axis parallel to the lateral axis of the aircraft, and the axis of the single gimbal is parallel to the longitudinal axis of the aircraft. A centring spring holds the gimbal level when there is no outside force acting on it. When the rotor is spinning, and the aircraft rotates about its vertical, or yaw, axis, a force is carried into the rotor shaft by the gimbal in such a way that one side of the shaft is moved forward while the other side is moved back. Precession causes the rotor to tilt, as the force is felt, at 90° to the point of application in the direction of rotor rotation. Mideast Aviation Academy 5.1-52 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Turn and slip indicator Rate Gyro inside Indicator Location of the turn coordinator on a turboprop aircraft’s basic-T layout Mideast Aviation Academy 5.1-53 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Turn coordinator A turn and slip indicator can show rotation about only the Instruments, either the turn and bank indicator or the turn vertical axis of the aircraft yaw. But since a turn is started by coordinator, have the standard rate turn clearly marked. Light banking the aircraft, that is, by rotating it about its longitudinal aircraft are equipped with 2-minute turn indicators while heavy axis, a turn indicator would be of more value if it sensed this aircraft are equipped with 4-minute turn indicators. This is very rotation also. useful to pilots who are out of visual contact with the ground and for air traffic control when appropriate separation of aircraft The mechanism of a turn coordinator is similar to that used in is desired. The pilot banks the aircraft such that the turn and a turn and slip indicator, except that its gimbal axis is tilted, slip indicator points to the standard rate turn mark and then usually about thirty degrees, so the gyro will precess when the uses a watch to time the turn. The pilot can pull out at any aircraft rolls, as well as when it yaws. This is especially handy desired direction depending on the length of time in the turn. since a turn and slip indicator is affected by adverse yaw at the beginning of a turn, but a turn coordinator senses enough roll A rate half turn (1.5° per second) is normally used when flying to cancel any deflection caused by adverse yaw. faster than 250 kt. The term rate two turn (6° per second) is used on some low-speed aircraft. Rather than using a needle for its indicator, the turn coordinator uses a small symbolic aircraft with marks on the dial opposite its wing tips. When the aircraft is turned at a standard rate to the left, the wings of the symbolic aircraft align with the mark on the left side of the instrument dial, the one marked ‘L’. When the rate of yaw is correct for the bank angle, the ball will be centred between the two lines across the inclinometer. Turn rates A standard rate turn for (light) aircraft is defined as a 3° per second turn, which completes a 360° turn in 2 minutes. This is known as a 2-minute turn, or rate one (= 180°/minute). For heavy aircraft, a standard rate turn is a 4-minute turn. Mideast Aviation Academy 5.1-54 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Turn coordinator indication and gyro rotor tilt Turn and slip indicator, and turn coordinator mechanisms Examples of turn coordinator indications Mideast Aviation Academy 5.1-55 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Compasses Direct reading compass Also known as magnetic compass, standby compass, whisky It requires no electrical power, except for its illumination at compass, ‘E’ type compass. night. It is a mandatory requirement for all aircraft under CS-25. Its main body is a cast aluminium housing, and one end is Remote reading compass covered with a glass lens. Across this is a vertical reference A remote reading compass is a device that measures the mark called a ‘lubber line’. Inside the housing and riding on a aircraft’s heading relative to the earth’s magnetic field steel pivot in a jewel post is a small brass float surrounded by electrically and sends the electronic data to an electronic a graduated dial which is part of a cone. Around the full 360° of display unit in the cockpit. the dial are 36 marks, representing the tens of degrees. Above every third mark is either a one or a two-digit number Early analogue devices were called flux valves, or flux gates, representing the number of degrees with the last zero left off. and provided a three-phase signal proportional to the magnetic field direction. The output of the flux valve is used to adjust the Zero is the same as 360° and is north. Nine is east, or 90°, 18 gyroscope which provides the heading change information. is south (180°), and 27 is 270° or west. Two small bar-type The flux valve maintains the gyroscope alignment with the permanent magnets are soldered to the bottom of the float, earth’s magnetic field. aligned with the zero and 18 marks, north and south. Due to the high cost of such a system, the flux valve was fitted The housing is filled with compass fluid, which is a hydrocarbon to larger aircraft only. On small aircraft, the pilot must manually product very similar to kerosene, but with certain additives that adjust the heading indicator by visual reference to the direct keep it clear. reading compass. This must be done before take-off and at least every 15 minutes during flight. The instrument is not very accurate. It is affected by magnetic components in the aircraft. Next to the compass is a compass Modern aircraft use a solid-state device called a magnetometer correction card. This card shows the errors that the particular (or magnetic heading sensor, or electronic compass). Modern compass has, at each of the main compass headings. magnetometers are relatively inexpensive and very reliable. Additionally, the compass heading is correct only if: the aircraft is horizontal; there is no acceleration; and the reading is corrected in accordance with the associated card. Mideast Aviation Academy 5.1-56 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Remote reading compasses (magnetometers) Direct reading compass with compass correction card Data from the flux valve makes corrections to the directional gyro – the gyro drives the indicator Mideast Aviation Academy 5.1-57 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Instrument layout Flight instruments are the instruments in the cockpit of an The magnetic compass will be above the instrument panel, aircraft that provides the pilot with information about the flight often on the windscreen centre post. situation of that aircraft, such as altitude, airspeed and direction. They improve safety by allowing the pilot to fly the aircraft in level flight, and make turns, without a reference outside the aircraft such as the horizon. Visual flight rules (VFR) require and airspeed indicator, an altimeter, and a compass or other suitable magnetic direction indicator. Instrument flight rules (IFR) additionally require a gyroscopic pitch-bank (artificial horizon), direction (directional gyro) and rate of turn indicator, plus a slip-skid indicator, adjustable altimeter, and a clock. Flight into Instrument meteorological conditions (IMC) require radio navigation instruments for precise take-offs and landings. The term is sometimes used loosely as a synonym for cockpit instruments as a whole, in which context it can include engine instruments, navigational and communication equipment. Many modern aircraft have electronic flight instrument systems. Most aircraft have four of the flight instruments located in a standardised pattern called the basic-T arrangement. The attitude indicator is in the top centre, airspeed to the left, altimeter to the right and heading indicator under the attitude indicator. The other two, turn-coordinator (if fitted) and vertical- speed indicator, are usually found under the airspeed and altimeter but are given more freedom in location. Mideast Aviation Academy 5.1-58 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 The four primary instruments in a turboprop aeroplane arranged in a basic-T Mideast Aviation Academy 5.1-59 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Stall warning Lift detector system The stall warning system is sensitive to the aircraft’s angle of When the data indicate an imminent stall, the computer attack. It provides no indication until the angle of attack has actuates both the stick shaker and an auditory alert. reached a critically high level, and the aircraft is close to stalling. The shaker itself is composed of an electric motor connected to a deliberately unbalanced flywheel. When actuated, the The sensor is a ‘lift detector’ switch, located at the leading edge shaker induces a forceful, noisy, and entyrely unmistakable of the wing. In all normal flight angle of attacks, the airflow shaking of the control yoke. This shaking of the control yoke forces the switch paddle down, and the circuit is switched off. matches the frequency and amplitude of the stick shaking that At a pre-defined high angle of attack, the airflow approaches occurs due to airflow separation in low-speed aircraft as they the switch paddle from beneath, which lifts it up, and the switch approach the stall. The stick shaking is intended to act as a closes the electrical circuit. backup to the auditory stall alert, in cases where the flight crew may be distracted. The electrical circuit is connected to a speaker in the cockpit. The audio warning is either a screeching sound or is a recorded In larger aircraft (especially in T-tailed jets that might be voice saying “Stall!” repeatedly. Some aircraft also annunciate vulnerable to deep stall), some stall protection systems also the stall visually on the central warning system. include a stick pusher system to automatically push forward on the elevator control, thus reducing the aircraft’s angle of attack Stick shaker system and preventing the stall. Larger aircraft use a stick shaker system, in addition to an aural and visual annunciator. Both systems have to be tested and armed before take-off and remain armed during flight. A stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke (the stick) of an aircraft to warn the pilot of an imminent stall. A stick shaker is connected to the control column of most civil jet aircraft. The stick shaker is a component of the aircraft’s stall protection system, which is composed of fuselage- or wing-mounted angle of attack (AOA) sensors that are connected to an avionics computer. The computer receives input from the AOA sensors and a variety of other flight systems. Mideast Aviation Academy 5.1-60 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Definition of angle of attack A lift detector switch on the leading edge of a wing Lift detector microswitch Typic stall annunciation Mideast Aviation Academy 5.1-61 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Angle of attack indicator An elaboration of the stall warning system is the simple angle of attack indicator that uses a pickup similar to the electric stall warning vane. But instead of a micro-switch to turn on a light or actuate a buzzer, the vane moves a synchro position sensor that drives the indicator. These vanes are often called ‘alpha’ (α) vanes, and the indicator is called an ‘alpha’ indicator. The angle of attack (alpha angle) is indicated on the EFIS display as shown below. The alpha angle signal can also be supplied to a stall computer which can then display the aircraft’s angle of attack relative to the stall angle and if necessary initiate stall protection systems (known as ‘alpha Prot’ and ‘alpha MAX’) such as stick shaker and/or throttle advance (Airbus A320, etc.) Many modern transport category aircraft have the vane installed on the side of the fuselage. Mideast Aviation Academy 5.1-62 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Alpha vane Angle of attack (alpha angle) display on a PFD Analogue angle of attack indicator Alpha Prot and Alpha Max 11A-9 082 Mideast Aviation Academy 5.1-63 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Glass cockpit (EFIS) Introduction An electronic flight instrument system (EFIS) is a flight deck instrument display system in which the display technology used is electronic rather than electromechanical. EFIS normally consists of a primary flight display (PFD), multi- function display (MFD) and engine indicating system (EIS). On a light aircraft, the EIS is normally (but not always) integrated into the MFD. The first EFIS units were installed on large commercial aircraft and did not attract much interest from the general aviation market. This was because cathode ray tube (CRT) displays were used, which were heavy and required a complex cooling system. Liquid crystal displays (LCD) are now exclusively used. These are light, inexpensive, do not generate excessive heat, and their attraction to the general aviation market is increased by the introduction of EFIS screens that can be fitted without modification of the instrument panel, so retrofitting of EFIS panels is common. Although relatively expensive to make the modification from ‘steam gauges’ to ‘glass cockpit’, the maintenance and upkeep are low, and reliability is high. Furthermore, expandability and options for future upgrades and add-ons are good since normally only a software change is required. Many avionics companies manufacture EFIS systems for light aircraft, both for new aircraft builds and for aftermarket customers. These include L3, Aspen Avionics, Chelton, Avidyne, and the highly popular manufacturer, Garmin. Mideast Aviation Academy 5.1-64 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 MFD (centre display unit) and PFD (left and right display units) of the Garmin G1000 Mideast Aviation Academy 5.1-65 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 EFIS overview The popular Garmin G1000 is used for the following overview stay in both the PFD and MFD to ensure accurate terrain of the EFIS architecture and displays. The system is typical, awareness information. and all other systems are similar. Primary flight display (PFD) The Garmin G1000 is an integrated flight instrument system The primary flight display shows the basic six flight instruments manufactured by Garmin typically composed of two display in ‘Basic-T’ configuration, including the airspeed indicator, the units, one serving as a primary flight display, and one as a altimeter, the heading indicator, and course deviation indicator. multi-function display. It serves as a replacement for most A small map called the ‘inset map’ can be enabled in the corner. conventional flight instruments and avionics. The buttons on the PFD are used to set the squawk code on Beyond that, additional features are found on newer and larger the transponder. The PFD can also be used for entering and G1000 installations, such as in business jets. This includes: activating flight plans. The PFD also has a ‘reversionary mode’ which can display all information normally shown on the MFD a third display unit, to act as a co-pilot PFD (for example, engine gauges and navigational information). an alphanumeric keyboard This capability is provided in case of an MFD failure. an integrated flight director/autopilot (without it, the G1000 interfaces with an external autopilot) Multi-function display (MFD) The multi-function display typically shows a moving map on the The display unit is available in two options, one has autopilot right side and engine instrumentation on the left. Most of the controls built in, the other option does not have autopilot other screens in the G1000 system are accessed by turning the controls. For this option, an autopilot control panel can be knob on the lower right corner of the unit. Screens available purchased separately at a later date. from the MFD other than the map include the setup menus, information about nearest airports and NAVAIDs, Mode-S Both the PFD and MFD each have two slots for SD memory traffic reports, terrain awareness, XM radio (where available), cards. The top slot is used to update the Jeppesen aviation and flight plan programming. database (also known as NavData) every 28 days, and to load software and configuration to the system. The aviation database must be current to use GPS for navigation during IFR instrument approaches. The bottom slot houses the world terrain and Jeppesen obstacle databases. While terrain information rarely changes or needs to be updated, obstacle databases can be updated every 56 days through a subscription service. The top card can be removed from the G1000 system following an update, but the bottom card must Mideast Aviation Academy 5.1-66 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Display unit and LRU installation Audio panel Mideast Aviation Academy 5.1-67 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 MEMS technology The magnetometer provides magnetic heading information to Microelectromechanical systems (MEMS) (also written as the autopilot and the display unit indications (HSI). It is normally micro-electro-mechanical, MicroElectroMechanical or connected to the AHRS (rather than the Integrated Avionics microelectronic and microelectromechanical systems and the Units directly) because the heading gyro (in the AHRS) is the related micromechatronics) is the technology of very small primary heading change sensor, and the Magnetometer devices. provides that gyro with a reference to the earth’s magnetic field. The aviation application of these is solid-state (no moving Transponder parts) transducers and sensors. For example, gyros and The minimum regulatory requirement is for a standard Mode-C pressure sensors utilising piezoelectric technology. transponder which replies to ATC interrogations while the optional Mode-S bidirectional communications with ATC can Attitude and heading reference system indicate traffic in the area as well as announce itself The system uses solid-state sensors (MEMS) to measure spontaneously via ‘squittering’ without prior interrogation. aircraft attitude, rate of turn, and slip and skid. This data is then provided to all the integrated avionics units and display units. A Mode-S transponder is required if any type of traffic The AHRS is the central attitude and heading sensor and awareness system is to be installed. If ADS-B is to be used, provides outputs to both the autopilot and to the display units then a special Mode-S transponder is required. for attitude and heading indication (via the integrated avionics units) Some other EFIS manufacturers combine the AHRS and ADC into one unit. This is called an ADAHRS (air data and attitude and heading reference system). Magnetometer The magnetometer measures aircraft heading and is a digital version of a traditional compass. It does so by aligning itself with the magnetic flux lines of the earth. It uses MEMS technology so has no moving parts. It is located in a remote part of the aircraft airframe, so it is far from any other aircraft electrical components that may cause magnetic deviation. Usually, it is located at a wing tip. Mideast Aviation Academy 5.1-68 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Mode-S transponder Integrated avionics unit Attitude and heading reference system (AHRS) Magnetometer Air data computer (ADC) Mideast Aviation Academy 5.1-69 Issue 02 – Revision 00 © Copyright 2021 FOR TRAINING PURPOSE ONLY May 2021 Module 11.5.1 Other system variations The Genesys Aerosystems IDU 680 EFIS provides all the same The Processor Units are effectively the video drivers. These are functionality as the Garmin G1000, but the architecture is integrated into the back of the display units. Unlike the Garmin slightly different. G1000, the NAV/COM and GPS are separate units. The GPS receiver is a WAAS/SBAS enabled ‘module’ which plugs Each EFIS consists of two display units. An aircraft can be a directly into the back of the processor units/display units. single EFIS or a dual EFIS system (the latter is the normal installation on training aircraft). The AHRS and ADC is a combined unit (ADAHRS) which also plugs directly into the back of the processor units/display units. Each Display Unit has two display areas, an upper and lower The only inputs to this module are the Pitot and Static p