AVIATION METEOROLOGY ATMOSPHERE • It is the envelope of homogenous mixture of gases called Air • It is attached to the Earth due to gravitation • It has no upper limit but it is believed that it extends upto 800 km 1.Characteristics: • It has weight and hence exerts pressure • It is compressible and expandable • It occupies space • It is a poor conductor of heat and electricity 2.Constituents: • Nitrogen – 78.09% • Oxygen –20.95% • Argon – 0.93% • Carbon dioxide – 0.035% • Traces of Neon, Xenon, Krypton, Helium, Methane, Hydrogen, Ozone, Nitrous Oxide, Ammonia, Sulphur Dioxide • In addition, Air contains water vapour and solid particles 3. Nitrogen and Oxygen constitute 99% of the atmosphere • Nitrogen : Oxygen :: 4:1 (by volume) • Nitrogen : Oxygen :: 3:1 (by weight) 4. Supplementary Oxygen is required once above 10,000ft. 5. The atmosphere has similar composition upto 80km known as Homosphere and above it Heterosphere. 6. Layers of atmosphere • Troposphere • Stratosphere • Mesosphere • Thermosphere • Ionosphere • Exosphere BASIC KNOWLEDGE OF TEMPERATURE, PRESSURE, DENSITY AND THEIR RELATIONSHIP 1. The atmospheric pressure at any level is the weight of the column of air of unit cross section extending vertically to the top of the atmosphere. 2. ICAO has adopted hPa as a unit to measure atmospheric pressure. 3. ICAO MSL pressure 1013.25 Pa = 760 mm Hg = 29.92 in 4. Pressure decreases with height. 5. Cold air is denser than warm air so, pressure will fall at a faster pace over a cold column of air than over a warm column of air. 6. Isobars are lines joining places of equal pressure. 7. Diurnal variation of pressure is large at above 3-5 hPa at equator due solar variation and very less over poles. 8. Pressure is measured by mercury barometer, where pressure is balanced by height of mercury column, but more preference is given to aneroid barometer, though not as accurate as mercury barometer, because of its ease of handling and use. 9. Altimeter is an aneroid barometer. 10. The lines joining places of equal height is called Contour. PRESSURE SETTINGS 1. QFE: It is pressure at aerodrome reference point or highest point on the runway. The altimeter reads zero or height of the altimeter from ARP, when subscale is set to QFE. It is also called Zero Setting. 2. QFF: It is the barometric pressure reduced to MSL, assuming the temperature of the place to be the temperature of the column of air extending up to MSL. Used for plotting on Synoptic charts and drawing isobars. 3. QNH: It is the station level pressure reduced to MSL assuming ISA conditions. When QNH is set on subscale, the altimeter indicates station elevation. This setting is useful for vertical separation of aircraft and from terrain. QNH should be updated from time to time as it changes with time and place due change in temperature and pressure. It is also called Absolute Altitude. 4. Regional QNH: This the forecast value of the lowest pressure expected in an altimeter setting region. It is issued every hour and valid for one hour. Correct use of it ensures adequate terrain separation. 5. QNE: It is the altitude indicated on altimeter and when subscale is set to 1013.25hPa .Normally QNE is used for high altitude airfields. Altimeter over reads when flying from a region of high pressure to low pressure. It also over reads when flying from region of high temperature to low temperature. Altimeter under reads when flying from a region of low pressure to high pressure. It also under reads when flying from region of low temperature to high temperature. TEMPERATURE: 1. Temperature is the measure of intensity of heat, measured using thermometer using Celsius and Fahrenheit scale. 2. Absolute Zero 1K= -273.16 3. 4. 5. 6. Surface temperature: The temperature measured at the height of 4ft (1.25m) above ground in shade (inside Stevenson’s Screen) 7. Heat: Sum total of the kinetic energy of all molecules and atoms of a substance. 8. Temperature is the average KE of all molecules and atoms of a substance. AIR DENSITY: 1. Density is defined as the mass of air contained in unit volume. 2. It’s unit is kg/m 3. As pressure increases, density increases, density altitude decreases. 3 4. 5. As humidity increases, density decreases, density altitude increases Factors affecting density: • As altitude increases – air is less dense • As temperature increases - air is less dense • As humidity increases - air is less dense ELEMENTARY KNOWLEDGE OF TERMS Visibility: The greatest distance at which a black object of suitable dimensions situated near the ground can be seen and recognised when observed against a bright background. OR The distance up to which prominent objects can be seen by naked eye and recognised as such under natural light. 1. Haze: Haze is suspension of very fine particles of small dust, water etc. Visibility in haze is 5000m or less. It gives a milky appearance to the atmosphere. • Dust haze: Dust kicked by strong winds in desert areas and semi arid areas is suspended in air called dust haze. It is thicker during day than at night because winds weaken at night. It is a summer hazard. Dust haze may extend from Rajasthan to Punjab, Haryana, UP, Bihar and adjoining states. Vertically it may extend to 6-8km. • Smoke haze: Smoke from industrial areas or domestic sources spread as a haze layer especially when the wind is calm or very light and there is strong ground inversion. 2. Mist: Mist is the suspension of water droplets in the atmosphere. In mist visibility is atleast 1000m but not more than 5000m. In mist relative humidity is almost 100% 3. Fog: It is the suspension of water droplets or ice crystals. In fog visibility is less than 1000m and relative humidity is nearly 100% Fog is divided into 3 categories – thick, moderate, light. It is cloud sitting on ground. Fog occurs due to condensation of water vapour present in the layers of air close to the ground. The condensation can occur either by cooling of air to dew point or by feeding moisture into the air to saturate it. 4. Smog: Smog is smoke and fog. It severely limits visibility and is a health hazard. CLOUDS • Cloud is an aggregate of visible water droplets or ice particles. • Clouds form due to adiabatic lifting and cooling of air until water vapour condenses as water drops or deposits as ice particles. The height at which this occurs is called Lifting Condensation Levels. 1.Classification: There are ten genera of clouds based on form and height. By form: Cumuliform, Stratiform and Cirriform By height: High, Medium, and Low A) High clouds: These clouds form at a height of 6-18km at tropics. They contain ice crystals and some of them may cause precipitation which remains confined to high/medium levels only. b) Medium clouds: In tropics, they occur about 2-8km and contain water droplets and ice crystals. They cause snow and rain. c) Low clouds: These clouds occur below 2km. 2. Types of clouds: High cloud: a) Cirrus [CI] – No precipitation b) Cirrostratus [CS] – Snow at high to medium levels c) Cirrocumulus [CC] – No precipitation Medium cloud: a) Altocumulus [AC] – No precipitation b) Altostratus [AS] – Ice accretion ( Rain and snow ) Low cloud: a) Stratus [ST] – Drizzle b) Stratocumulus [SC] c) Nimbostratus [NS] – Ice accretion, continuous precipitation Clouds with vertical development: a) Cumulus [CU] – Rain b) Cumulonimbus [CB] – Showers, hail 3. Cloud ceiling: The height above the ground or water surface of the lowest layer of the cloud below 6000m (20000ft) covering more than half of the sky (5/8 or more). 4. Flying conditions in clouds: • Stratiform Clouds Flying in Stratiform Clouds (CS and AS) is generally smooth even during monsoon months when cloud layers of AS and NS are thick. In NS visibility is reduced due to continuous precipitation and in the presence of Stratus, reduced slant visibility causes difficulty locating the runway during the landing. Ice accretion occurs in NS and AS clouds above freezing level. • Cumuliform Clouds CC and AC may cause some amount of turbulence. Fair weather CU and SC may cause bumpiness while flying through. Well developed CU, TCU and CB cause serious aviation hazards like severe turbulence, hail, strong up and downdraughts, gusts, ice accretion, lightning etc. Flying through CB is strictly prohibited. Even areas 10 to 20 KM around an active CB cloud are prone to turbulence. Squalls associated with CB adversely affect landing and take-off hence, such operations should be avoided during TS. METAR Aviation routine weather report issued every half an hour or at hourly intervals SPECI- Aviation Selected Special Weather report. Issued at any time. AIR REGULATIONS 1. Aerodrome (AD): A defined area on land or water (including any buildings, installations and Aerodrome equipment intended to be used either wholly or in part for arrival, departure and surface movement of aircraft. 2. Balloon: means a non-power driven lighter than air aircraft 3. Co-pilot: A licensed pilot serving in any piloting capacity other than as pilot-in-command but excluding a pilot who is on board the aircraft for the sole purpose of receiving flight instruction. 4. Director General: means director general of civil aviation 5. Flight time: The total time from the moment an aircraft first moves for the purpose of taking off until the moment it finally comes to rest at the end of the flight. 6. Solo Time: Flight time during which a pilot is the sole occupant of an aircraft. 7. Dual Time: Flight time during which a person is receiving flight instruction from a pilot on board the aircraft. 8. Flight Crew Member. A licensed crew member charged with duties essential to the operation of an aircraft during flight time. 9. Helicopter: means a heavier than air aircraft supported in flight by the reactions of the air on one or more power driven rotors on substantially vertical axis 10. Prohibited Area. Airspace of defined dimensions above the land areas or territorial waters of a State within which flight of aircraft is prohibited. 11. Take off: It is the phase of the flight in which an aircraft goes from the ground to flying in the air 12. Landing: It is the last part of a flight where an aircraft returns to the ground. 13. Mayday: Mayday is an emergency procedure word used internationally as a distress signal in voice procedure radio communication. 14. PAN: Three calls of Pan-Pan are used in radiotelephone communications to signify that there is an urgency onboard ship, aircraft or other vehicle for the time being there is no immediate danger to anyone’s life or to the vessel itself. 15. Aeroplane: A power driven heavier than air aircraft, deriving its lift in flight chiefly from aerodynamic reactions on surfaces which remain fixed under given conditions of flight. 16. Aircraft: Any machine that can derive support in the atmosphere from the reactions of the air other than the reactions of the air against the earth’s surface and includes balloons whether fixed or free, airships, kites, gliders and flying machines. 17. Log Book: It is a record of a pilot’s flying hours. It contains every flight a pilot has flown, including flight time, number of landings and number of instrument approaches. DIFFERENT CATEGORIES OF PILOT’S LICENSES 1. Student Pilot’s License (for aeroplanes, helicopters, gliders, balloons and micro light aircraft) 2. Private Pilot’s License (for aeroplanes and helicopters) 3. Commercial Pilot’s License (for aeroplanes and helicopters) 4. Airline Transport Pilot’s License (for aeroplanes and helicopters) 5. Instrument Rating (for aeroplanes and helicopters 6. Assistant Flight Instructor’s Rating (for aeroplanes and helicopters) 7. Flight Instructor’s Rating (for aeroplanes, helicopters, gliders and balloons) 8. Pilot’s License (gliders, balloons and micro light aircraft) 9. Student Flight Navigator’s License 10. Flight Navigator’s License 11. Student Flight Engineer’s License 12. Flight Engineer’s License 13. Flight Radio Telephone Operator’s License 14. Flight Radio Telephone Operator’s License (Restricted) STUDENT PILOT LICENSE REQUIREMENTS • Age- Applicant shall not be less than 16 years of age on the date of application • Educational Qualification- Shall have passed class 10 • Medical Fitness- Class II medical certificate • Knowledge- He shall pass oral examination in Air Regulations, Aviation Meteorology, Air Navigation and Aircraft and Engines as per the syllabus prescribed by the director general unless he previously held a pilot’s license of a higher category, or is able to produce evidence in a manner prescribed by the Director General that is well versed with the aforesaid subjects. th VALIDITY • 5 years PRIVELEGES • Holder of SPL is entitled to fly within Indian Territory only as PIC in any aeroplane entered in the aircraft rating of his license • He shall fly at all times under the authority and supervision of a flight instructor or an approved examiner • He shall only fly under Visual Flight Rules only • He shall not carry passengers, animals and goods for hire, reward or remuneration of any kind • He shall not undertake cross-country flights unless he has a minimum of 10hrs or solo flight time and has passed the examination in Air Navigation and Aviation Meteorology. Student Pilot’s License shall be issued by a flying club/ Government Flying Training School specifically authorised in this regard and subject to conditions as laid down by the Director General. LIGHT AND PYROTECHNIC SIGNALS VISUAL GROUND SIGNALS • Prohibition of landing A horizontal red square panel with yellow diagonals when displayed in a signal area indicates that landings are prohibited and that the prohibition is liable to be prolonged. • Need for special precautions while approaching or landing A horizontal red square panel with one yellow diagonal when displayed in a signal area indicates that owing to the bad state of the maneuvering area, or for any other reason, special precautions must be observed in approaching to land or in landing. • Use of runways and taxiways A horizontal white dumb-bell when displayed in a signal area indicates that aircraft are required to land, take off and taxi on runways and taxiways only. • Maneuvers not confined to runways and taxiways A white dumb-bell with black stripes signifies that take-offs and landing are to be on a runway, but movement on the ground is not confined to pavements • Closed runways or taxiways Crosses of a single contrasting color, yellow or white played horizontally on runways and taxiways or parts thereof indicate an area unfit for movement of aircraft. • Glider flights in operation A double white cross displayed horizontally in the signal area indicates that the aerodrome is being used by gliders and that glider flights are being performed. • Air Traffic Services Reporting Office The letter C displayed vertically in black against a yellow background indicates the location of the air traffic services reporting office. • Direction for landing or take off A white “T” signifies that take-offs and landing shall be in the direction of the shaft of the “T” (as indicated by the arrow). • Right Hand Traffic A red and yellow striped arrow signifies that a righthand circuit is in force. . • QDM Boards A yellow board with two black numbers on is situated on the tower, and indicates the runway direction in use. • Signals Mast The following signals are flown from the signals mast: RUNWAY DETAILS VISUAL FLIGHT RULES (VFR) VFR is only permitted in VMC VMC Criteria Classes A, B, C, D and E Airspace. • At and above 10 000 ft (FL100) the flight visibility requirement is 8 km with 300 m (1000 ft) vertically, and 1500 m horizontally from cloud. • Below 10 000 ft (FL100) the flight visibility requirement is reduced to 5 km. VMC Criteria Classes F and G Airspace • At and above 10 000 ft (FL100) the flight visibility requirement is 8 km with 300 m (1000 ft) vertically, and 1500 m horizontally from cloud. • Below 10 000 ft (FL100) but above 3000 ft, the flight visibility requirement is reduced to 5 km. • Below 3000 ft AMSL and within 1000 ft of the surface (where surface elevation is above 3000 ft) the flight visibility remains 5 km but VMC would exist if the aircraft was clear of cloud and within sight of the surface. When clearance is obtained from Air Traffic Control VFR flights shall not take off or land at an aerodrome within a control zone or enter the aerodrome traffic zone or traffic pattern- a. When ceiling is less than 450m, or b. When ground visibility is less than 5 km. VFR flights shall not be operated- a. Above FL150 b. At transonic and subsonic speeds c. More than 100NM seaward from the shoreline within controlled airspace. To operate VFR above FL290 a vertical separation of 300m (1000ft) is maintained VFR flights shall not be flown – a. Over congested areas, towns, settlements, assembly of people at a height less than 300m above the highest obstacle within a radius of 600m from the aircraft. b. Shall not be flown at a height less than 150m above water or ground. AIR NAVIGATION ➢ General Navigation • Earth’s shape is commonly described as an oblate spheroid, that is, a sphere which is slightlyflattened at its poles. • The flattening is called compression and in the case of the Earth is approximately0.3% (1/300th). • ICAO has adopted WGS 84 as the world standard. • Great Circle: A circle on the surface of the Earth whose centre and radius are those of theEarth itself is called a Great Circle. It is called ‘great’ because a disc cut through the Earth inthe plane of the Great Circle would have the largest area that can be achieved. • The shortest distance between two points on the Earth’s surface is the shorter arc of theGreat Circle joining the two points. • Given two points on the Earth’s surface, there will be only one Great Circle joining them(unless the points are diametrically opposed). • The Great Circle whose plane is at 90° to the axis of rotation of the Earth (the polar axis) is called the Equator.It lies in an East-West direction and divides the Earth equally into two hemispheres. For the definition of position on the Earth, the Equator is the datum for defining Latitude. • Meridians are semi-Great Circles joining the North and South poles. All meridians indicate True North-South direction. Every Great Circle passing through the poles forms a meridianand its Anti-meridian. The meridians cross the Equator at 90°. • A circle on the surface of the Earth whose centre and radius are not those of the Earth is called a Small Circle. The main small circles of relevance to position are the Parallels of Latitude. • The latitude of any point is the arc (angular distance) measured along the meridian through the point from the Equator to the point. • The longitude of any point is the shorter distance in the arc along the Equator between the Prime Meridian and the meridian through the point. • A Rhumb Line is a regularly curved line on the surface of the Earth which cuts all meridiansat the same angle - a line of constant direction. Examples of common Rhumb Lines are: • Parallels of Latitude (because they cut all meridians at 90°). • Equator (a special case because the Equator is also a Great Circle). • Meridians (are also Great Circles and the cut angle involved is 0°). IMPORTANT CONVERSIONS 1 meter (m) = 100 centimeters (cm) = 1000 millimeters (mm) 1 centimeter (cm) = 10 millimeters (mm) 1 meter (m) = 3.28 feet (ft) 1 foot (ft) = 12 inches ( ‘in’ or “ ) 1 inch (in) = 2.54 centimeters (cm) 1 yard (yd) = 3 feet (ft) • The Kilometer (km). The definition of the kilometer is 1/10 000th of the average distanceon the Earth between the Equator and either Pole. 1 kilometer (km) = 3280 feet (ft) • The Statute Mile (stat.m). Although the statute mile (5280 feet) is widely used on the groundit is hardly ever used in aviation nowadays. Older airspeed indicators used to be calibrated inmph, and still are for some American light aircraft, but this is now rare. • The Nautical Mile (NM). The nautical mile is the most important large measure of distanceused in aviation because it can be related directly to the angular measurements of the Latitude/Longitude graticule of the Earth. • The ICAO definition of the nautical mile is that it is a measure of distance of 1852 meters. • The Standard Nautical Mile is defined as a length of 6080 feet. • One minute of latitude = 1 nautical mile (NM) One degree of latitude = 60 minutes = 60 NM. • One minute of longitude = 1 NM AT THE EQUATOR ONLY. • The full definition of the length of a nautical mile is that length of arc of a Great Circle whichsubtends an angle of one minute at the centre of curvature of the Earth’s surface. • There are 3 general types of projection surfaces: • Azimuthal/Plane • Cylindrical • Conical WE USE LAMBERT’S CONFORMAL CHARTS • MAGNETIC COMPASS Magnetic North is the horizontal direction indicated by a freely suspended magnet influenced only by the Earth’s magnetic field. • Variation is the angle between True and Magnetic North and is measured in degrees Eastor West from True North. • A line on the surface of the Earth joining points of equal magnetic variation is called anIsogonal. • The line connecting points of zero variation is called the Agonic Line. • The maximum possible value of variation is 180° and this occurs at both the Northand the South Poles. • Deviation is defined as the angle measured at a point between the direction indicated by acompass needle and the direction of Magnetic North. • Isoclinals are lines on a map or chart joining places of equal magnetic dip. • Aclinic Lines is the name given to isoclinals joining places of zero dip. • Compass Swing : • The basic method of determining deviation is to compare the aircraft’s heading compassreading with magnetic heading as defined by a high quality ‘land or datum’ compass. Thiscomparison of aircraft compass and magnetic datum readings is carried out in an area selected specifically for this purpose. Therefore the aims of a compass swing are as follows: • To observe / determine the deviations / differences between magnetic north (observed on a landing compass) and compass north (observed in the aircraft) on a series of headings • To correct / remove as much deviation as possible • To record the residual deviation which is left after the compass has been adjusted. Occasions for Swinging the Compass :• When compass components are installed or replaced. • Whenever the accuracy of the compass is in doubt. • After a maintenance inspection if required by the schedule. • After a significant aircraft modification, repair or replacement involving magnetic material. • When carrying unusual ferromagnetic payloads. • When the compass has been subjected to significant shock. • If the aircraft has been struck by lightning. • After significant modification to aircraft radio/electrical systems. • After the aircraft has been given a new theatre of operations if the move involves a largechange of magnetic latitude. • If the aircraft has been in long term storage standing on one heading. Hard Iron Magnetism :The total force at the compass positionproduced by permanent hard iron magnetismcan be resolved into three components. Thesecomponents will be fixed for a given aircraftand will not change with change of heading. • Soft Iron Magnetism :If the deviations caused by the blue pole in thenose are plotted against compass heading,a positive sine curve is obtained. Had theblue pole been aft of the compass a negativesine curve would have been obtained. This would mean that on a heading of 090° thedeviation would reach a maximum westerlyvalue instead of a maximum easterly value.The changes in directive force would also berevised, the maximum occurring on 180° andthe minimum on 360°. • Correction of Coefficients :Coefficient A - a mechanical problem of a displaced lubber line. Coefficient B - correction required because of magnetic deviating forces acting upon the DRMC or the detector unit and giving errors known as deviation. Done on an easterly or westerly heading. Coefficient C - correction required because of magnetic deviating forces acting upon the DRMCor the detector unit and giving errors known as deviation. Done on a northerly or southerly heading. ➢ Instrument Navigation Airspeed Indicator Principle of Operation An aircraft on the ground in still air is subject only to atmospheric (static) pressure (S). However,in flight, the leading edges of an aircraft are subject to an additional (dynamic) pressure. This results in a total (pitot) pressure (P) on the leading edges of dynamic pressure plus staticpressure. Pitot = Dynamic + Static The pitot head senses pitot pressure and the static/vent senses static pressure. These twopressures are fed to the airspeed indicator, a differential pressure gauge, which measures theirdifference (the dynamic pressure). Dynamic pressure is related to airspeed, because:Dynamic Pressure = ½ ρV² where V is true airspeed (TAS) and ρ is the density of the surrounding air The ASI measures airspeed by measuring dynamic pressure. Construction ASI Errors • Instrument Error. Manufacturing imperfections and usage result in small errors which aredetermined on the ground under laboratory conditions by reference to a datum instrument.A correction card can be produced for the speed range of the instrument. • Position Error. Alternatively known as ‘pressure’ error, this arises mainly from the sensing ofincorrect static pressure, and is described more fully in the section entitled Pressure Heads.Position errors throughout the speed range are determined by the aircraft manufacturer during the test flying programme for a particular aircraft type.It is not unusual to compile a joint correction card for position and instrument errors and placeit in the aircraft near the ASI concerned. • Maneuver-induced Errors. These are associated chiefly with maneuvers involving change inangle of attack, giving transient errors and a lag in the indication of changes in airspeed. IAS is Indicated Airspeed CAS is IAS corrected for Instrument and Position (Pressure) Error. Equivalent Airspeed is CAS corrected for Compressibility Error only. EAS + Density Error = TAS ASI Color Coding The White Arc denotes the flap operating range, from stall at maximum AUW in the landing configuration (full flap, landing gear down, wings level, power-off) up to VFE(maximum flaps extended speed). The Green Arc denotes the normal operatingspeed range, from stall speed at maximumall-up weight (flaps up, wings level) up to VN(‘normal operating limit speed’ or ‘maximumstructural cruising speed’) which should not be exceeded except in smooth air. Operationsat IASs in the green arc should be safe in allconditions, including turbulence. The Yellow Arc denotes the caution range,which extends from VNO (normal operating limit speed) up to VNE (the never exceed speed).The aircraft should be operated at IASs in the caution range only in smooth air. A Red Radial Line denotes VNE, the never exceed speed. A blue radial line denotes the best rate of climb speed for one engine out, maximum weight,at mean sea level (VYSE). With a blocked static source, the ASI over-reads in a descent. ‘Pitot Blocked: – Under-reads in Descent Static Blocked: – Over-reads in Descent’ Pressure Altimeter Principle of Operation The pressure altimeter is a simple, reliable, pressure gauge calibrated to indicate height. The pressure at a point depends on the weight of the column of air which extends vertically upwardsfrom the point to the outer limit of the atmosphere. The higher an aircraft is flying, the shorter is the column of air above it and consequently thelower is the atmospheric pressure at the aircraft. In other words, the greater the height, the lower the pressure, and by measuring the pressurethe altimeter measures height. Unfortunately, the relationship between pressure and height is not a linear one, so thatcalibration of the altimeter scale is not a simple matter. Static pressure is fed into the case of the instrument from the static source. As heightincreases, static pressure decreases and the capsule expands under the control of a leaf spring. A mechanical linkage magnifies the capsule expansion and converts it to a rotational movementof a single pointer over the height scale. Altimeter Errors The errors which affect altimeters are many and the extent of some of them varies withaltimeter type. Much effort is expended on improving instrument accuracy, and the permissibletolerances of modern altimeters are smaller than with earlier types. There are other errors caused by deviation of the actual atmosphere from standard conditions, and also the difficulty in sensing correctly the outside air pressure. A list of the main errorsfollows. Position (or Pressure) Error This is largely due to the inability to sense the true static pressure outside the aircraft, asdescribed in the chapter on Pressure Heads. The error is usually small but increases at high Machnumbers (and, consequently, at high altitudes usually associated with high Mach numbers). Instrument Error Manufacturing imperfections, including friction in the linkage, cause errors throughout theoperating range. The errors are kept as small as possible by adjustments within the instrument,and the calibration procedure ensures that they are within permitted tolerances. Residualerrors may be listed on a correction card. Maneuver-induced Error This is caused by transient fluctuations of pressure at the static vent during change of, mainly,pitch attitude and delays in the transmission of pressure changes due to viscous and acousticeffects in the static pipeline. Barometric Error Providing the altimeter has a pressure subscale, and the local pressure is set on it, the altimeterwill indicate height AMSL (though still subject to the other errors). If the local surface pressurehas changed since the pressure value was set, a ‘barometric’ error of roughly 30 feet perhectopascal will result. If pressure has fallen, the altimeter over-reads. Blockages and Leaks If the static source becomes blocked, thealtimeter will not register any change in height- the height at which the blockage occurredwill still be indicated regardless of any climbor descent. On many aircraft, an alternativesource of static pressure will be available. Should the static line fracture in a pressurizedaircraft, the altimeter will show the (lower)cabin altitude rather than aircraft altitude A fracture in the static line within anunpressurized aircraft will normally result inthe altimeter over-reading, due to the pressurein the cabin being lower than ambient dueto aerodynamic suction. If the aircraft is CLIMBING then the altimeterwill UNDER-READ. If the aircraft is DESCENDING then the altimeter will OVER-READ. The amount of the error will increase as the aircraft moves away from the height at which theblockage occurred. ➢ Radio Navigation VHF Direction Finder (VDF) o The VHF Direction Finder (VDF) is a means of providing a pilot with the direction to fly towards a ground station - a bearing. o Available on 118.0 - 137 MHz (Emission Code A3E). o VHF International Distress Frequency – 121.5 MHz. A VDF station will provide the following as requested: • QDR Aircraft’s Magnetic Bearing from the station (Radial); used for en route navigation • QDM Aircraft’s Magnetic Heading to steer (assuming no wind) to reach the VDF station; used mainly for station homing and let-downs using published procedures • QTE Aircraft’s True Bearing from the station; used for en route navigation • QUJ Aircraft’s True Track to the station; not generally used The accuracy of the observation is classified as follows: • Class A – Accurate within ± 2° • Class B – Accurate within ± 5° • Class C – Accurate within ± 10° • Class D – Accuracy less than Class C Principle of Operation A VHF voice communications radio produces a vertically polarized signal; therefore, the groundantenna is vertically polarized and has an array of vertical elements arranged in a circle Range of VDF • As VDF utilizes the VHF Band (or UHF as required) the range will obey the line of sight formula: the higher the transmitters the greater the reception range Line of sight Range (MTR) = Affected by : Power of Transmitters Intervening High Ground Atmospheric Conditions (Ducting) Accuracy: Propagation Error Site Error Aircraft Attitude Overhead Fading Due to Multi-path Signals Automatic Direction Finder (ADF) Automatic Direction Finder (ADF) equipment in the aircraft is used in conjunction with a simplelow and medium frequency non-directional beacon (NDB) on the ground to provide an aid fornavigation and for non-precision approaches to airfields. The ADF measures the bearing of an NDB relative to the fore/aft axis of theaircraft. The Non-directional Beacon (NDB) is a ground based transmitter which transmits verticallypolarized radio signals, in all directions (hence the name), in the Low Frequency (LF) andMedium Frequency (MF) bands. Frequencies: 190 - 1750 kHz There are two types of NDB in current use: • Locator (L)- These are low powered NDBs used for airfield or runway approach procedures or are co-located with, and supplement, the outer and middle markers of an ILS system. They normally have ranges of 10 to 25 NM and may only be available during an aerodrome’s published hours of operation. • En route NDBs- These have a range of 50 NM or more, and where serving oceanic areas may have ranges of several hundred miles. They are used for homing, holding, en route and airways navigation. The aircraft equipment comprises: • A loop aerial • A sense aerial • A control unit • A receiver • A display Uses of NDB Homing, Holding, Approach, En route nav-aid Errors • Static interference (precipitation and thunderstorms) • Station interference • Night effect • Mountain effect • Coastal refraction • Quadrantal error • Bank angle (dip) • Lack of failure warning VHF Omni-directional Range (VOR) The VHF Omni-directional Range (VOR) was adopted as the standard short range navigationaid in 1960 by ICAO. It produces bearing information usually aligned with magnetic north atthe VOR location. It is practically free from static interference and is not affected by sky waves,which enables it to be used day and night. When the VOR frequency is paired with a co-locatedDistance Measuring Equipment (DME) an instantaneous range and bearing (Rho-Theta) fix isobtained. Principle of Operation Phase comparison of two 30 Hz signals, one is frequency modulated and the other is amplitude modulated. • The reference signal is FM. • The variable phase directional signal is AM. Vice-versa for a Doppler VOR. Uses: Airways Airfield let-downs Holding points En route navigation Transmission Details: VOR beacons operate within the VHF band (30-300 MHz) between 108.0 - 117.95 MHz asfollows: • 40 channels, 108-112 MHz: This is primarily an ILS band but ICAO has allowed it to be shared with short range VORsand Terminal VORs (TVOR): 108.0, 108.05, 108.20, 108.25, 108.40, 108.45 ….. 111.85 MHz(even decimals and even decimals plus 0.05 MHz) • 120 channels, 112 - 117.95 MHz (a channel every 0.05 MHz): The emission characteristics are A9W: A = main carrier amplitude modulated double side-band. 9 = composite system. W = combination of telemetry, (telephony) and telegraphy. Types of VOR: CVOR-Conventional VOR is used to define airways and for en-route navigation. BVOR-A broadcast VOR which gives weather and airfield information between beaconidentification. DVOR-A Doppler VOR - this overcomes siting errors. TVOR-Terminal VOR which has only low power; and is used at major airfields. VOT-This is found at certain airfields and broadcasts a fixed omnidirectional signalfor a 360° test radial. This is not for navigation use but is used to test an aircraft’sequipment accuracy before IFR flight. More than +/-4° indicates that equipmentneeds servicing. VORTAC-Co-located VOR and TACAN (DME) beacons. DBVORTAC-Combination. Accuracy affected by: Site error (less with DVOR) Propagation error Scalloping (bending due to reflections from terrain) Airborne equipment error (+/- 3°) Airborne equip: Aerial, Receiver, Display (CDI/RMI) CDI: 2° per dot; max 10°; relationship between indication and aircraft position. RMI: arrowhead gives QDM; tail gives QDR; Use magnetic variation at station. Instrument Landing System (ILS) The Instrument Landing System (ILS) has been in existence for over 40 years and is still the most accurate approach and landing aid in current use. The system provides pilots with an accurate means of carrying out an instrument approach to a runway, giving guidance both in the horizontal and the vertical planes. ILS Frequencies Localizer The Localizer operates in the VHF band between 108 and 111.975 MHz to provide 40 channels,e.g. 108.1 108.15; 108.3 108.35; 108.5 108.55 -111.95 MHz. This part of the frequency band isshared with VOR: the frequencies allocated are odd decimals and odd decimals + 0.05 MHz. Glide Path The glide path operates in the UHF band between 329.15 and 335 MHz to provide 40complementary channels. e.g. 329.15, 329.3, 329.45, 329.6 - 335 MHz. Markers All markers transmit at 75 MHz. There is no interference problem as the radiation pattern is anarrow fan-shaped vertical beam. The localizer (LLZ) transmits in the VHF band and is located about 300 m from the up-wind endof the runway. The glide path (GP) transmitter operates in the UHF band, and is frequency paired with thelocalizer. It is located 300 m in from the threshold and about 200 m from the runway edgeabeam the touchdown point. Marker beacons transmit at 75 MHz in the VHF band. These include the outer marker (OM),the middle marker (MM) and possibly an inner marker (IM). ILS Principle of Operation Uses difference in depth of modulation between 2 overlapping lobes. Localizer Right hand lobe – 150 Hz modulation Left hand lobe – 90 Hz modulation Glide Slope – Upward lobe – 90 Hz modulation Downward lobe – 150 Hz modulation ILS Coverage Localizer The localizer coverage sector extends from the transmitter to distances of: • 25 NM (46.3 km) within plus or minus 10° from the centre line. • 17 NM (31.5 km) between 10° and 35° from the centre line. • 10 NM (18.5 km) outside ± 35° if coverage is provided. These limits may be reduced to 18 NM within 10° sector and 10 NM within the remainder ofthe coverage when alternative navigational facilities provide satisfactory coverage within theintermediate approach area. Glide Path The glide path coverage extends from the transmitter to a distance of at least: 10 NM (18.5 km) in sectors of 8° in azimuth on each side of the centre line. The vertical coverage is provided from 0.45θ up to 1.75θ above the horizontal where θ is thepromulgated glide path angle. The lower limit may be reduced to 0.3θ if required to safeguardthe promulgated glide path intercept procedure. ILS Categories (ICAO) Category I A category I ILS is one which provides guidance information from the coverage limit of the ILSto the point at which the localizer course line intersects the ILS glide path at a height of 200 ft(60 m) or less above the horizontal plane containing the threshold. Category II An ILS which provides guidance information from the coverage limit of the ILS to the point atwhich the localizer course line intersects the ILS glide path at a height of 50 ft (15 m) or lessabove the horizontal plane containing the threshold. Category III An ILS, which with the aid of ancillary equipment where necessary, provides guidanceinformation from coverage limit of the facility to, and along, the runway surface. TECHNICAL GENERAL • Density- Density is defined as mass per unit volume. The unit for density 3 3 is kg/m or g/m . Sea level density- 1225 g/m . Density varies with static pressure, temperature and humidity. 3 • Pressure- Static pressure is the weight of the atmosphere pressing down 2 on the air beneath. The unit for static pressure is N/m or hpa. Sea level pressure- 1013.25 hpa. • Temperature-It is the measure/intensity of heat. It is degrees Celsius (or centigrade) when measured relative to the freezing point of water, or Kelvin when measured relative to absolute zero. • Humidity-The amount of water vapour contained in a given amount of air. Relationship between the above defined terms is as follows: Density ∝ Pressure ∝ 1/ Temperature ∝ 1/Humidity • Thrust- Thrust is the force needed to overcome the resistance of air (drag) to the passage of an aircraft. Thrust is generated by the engines. To maintain level flight at constant speed, constant thrust is required; to climb or descend the aircraft whilst maintaining constant speed, the thrust must be increased or decreased; to increase or reduce the speed of the aircraft whilst maintaining level flight, the thrust must be increased or decreased. • Drag- Drag is the force which resists the forward motion of the aircraft. Drag acts parallel to and in the same direction as the relative airflow (in the opposite direction to the flight path). • Lift- Lift is defined as the net force generated normal (at 90°) to the relative airflow or flight path of the aircraft. The aerodynamic force of lift results from the pressure differential between the top and bottom surfaces of the wing. • Weight- Weight is the force generated by the gravitational attraction of the earth on the airplane. • Aerofoil- A shape capable of producing lift with relatively high efficiency. • Angle of attack- The angle between the chord line and the Relative Airflow. • Centre of lift- It is the point where the sum total of all lift generated by parts- principally by wings, control surfaces and aerodynamic fuselage parts balances out and the aggregate direction their force will act on an aircraft while in atmosphere. • Stall- Stall is defined as a sudden reduction in the lift generated by an aerofoil when the critical angle of attack is reached or exceeded. • Range- The maximum total distance an aircraft can fly between takeoff and landing as limited by fuel capacity in powered aircraft or crosscountry speed and environmental conditions in unpowered flight. • Endurance- Endurance is the maximum length of time an aircraft can spend in cruising flight. It is different from range which is a measure of distance flown. The forces acting on an aerofoil in level flight are- 1. Lift 2. Drag 3. Thrust 4. Weight Bernoulli’s Theorem In the steady flow of an ideal fluid the sum of the pressure energy and the kinetic energy remains constant. An ideal fluid is both incompressible and has no viscosity. This statement can be expressed as: Pressure + Kinetic energy = Constant or: p + 1/2 ρ V2 = Constant Bernoulli’s theorem is used to explain the flight of an aircraft. The airflow velocity over the top surface of a lifting aerofoil will be greater than that beneath, so the pressure differential that results will produce a force per unit area acting upwards. The larger the surface area, the bigger the force that can be generated. Primary controls of an aircraft 1. Rudder for control in yaw about the normal axis (directional control). 2. Elevator for control in pitch about the lateral axis (longitudinal control). 3. Ailerons for control in roll about the longitudinal axis (lateral control). Trimming ➢ An airplane is trimmed when it will maintain its attitude and speed without the pilot having to apply any load to the cockpit controls. The aircraft may need to be trimmed in pitch as a result of: • changes of speed • changes of power • varying CG positions • changes of configuration ➢ Trimming in yaw will be • • needed: on a multi-engine aircraft if there is asymmetric power. as a result of changes in propeller torque. ➢ Methods of Trimming Various methods of trimming are in use. The main ones are: • the trimming tab. • variable incidence (trimming) tailplane. • spring bias • CG adjustment. • adjustment of the artificial feel unit. ➢ Use of a trim tab A trim tab is a small adjustable surface set into the trailing edge of a main control surface. Its deflection is controlled by a trim wheel or electrical switch in the cockpit.To maintain the primary control surface in its required position, the tab is moved in the opposite direction to the control surface until the tab moment balances the control surface hinge moment. ➢ Variable Incidence (Trimming) Tailplane This system of trimming may be used on manually operated and power operated controls. To trim, the tailplane incidence is adjusted by the trim wheel until the tailplane load is equal to the previous elevator balancing load required. The main advantages of a variable incidence (trimming) tailplane are: • The drag is less in the trimmed state as the aerofoil is more streamlined. • Trimming does not reduce the effective range of pitch control as the elevator remains approximately neutral when the aircraft is trimmed. • It is very powerful and gives an increased ability to trim for larger CG and speed range. The disadvantage of a variable incidence (trimming) tailplane is that it is more complex and is heavier than a conventional trim tab system. ➢ Spring Bias In the spring bias trim system, an adjustable spring force is used to decrease the stick force. No tab is required for this system ➢ CG Adjustment If the flying controls are used for trimming, this results in an increase of drag due to the deflected surfaces. The out of balance pitching moment can be reduced by moving the CG, thus reducing the balancing load required and therefore the drag associated with it. ➢ Artificial Feel Trim If the flying controls are power operated, there is no feedback of the load on the control surface to the cockpit control. The feel on the controls has to be created artificially. When a control surface is moved, the artificial feel unit provides a force to resist the movement of the cockpit control. To remove this force (i.e. to trim) the datum of the feel unit can be adjusted so that it no longer gives any load on the flight deck controls. . Flaps A flap is a hinged portion of the trailing or leading edge which can be deflected downwards and so produce an increase of camber. They are primarily used to reduce the take-off and landing distances. This permits operation at greater weights from given runway lengths and enables greater payloads to be carried For low speed aerofoils the flaps will be on the trailing edge only, but on high speed aerofoils where the leading edge may be symmetrical or have a negative camber, there will usually be flaps on both the leading edge and the trailing edge. Different type of flaps areo Plain flap o o o o o Slotted flap Fowler flap Slotted flap Krueger flap Variable camber flaps Landing gears Landing gear is the undercarriage of an aircraft which may be used for take-off and landing. The functions of the landing gear are: 1. To provide a means of manoeuvring the aircraft on the ground. 2. To support the aircraft at a convenient height to give clearance for propellers and flaps, etc. and to facilitate loading. 3. To absorb the kinetic energy of landing and provide a means of controlling deceleration. Operation of a piston engine An aircraft piston engine, also commonly referred to as a reciprocating engine is an internal combustion engine that uses one or more reciprocating pistons to convert pressure into a rotational motion. It works on the principle of conversion of mechanical energy into heat energy. Otto cycle (an idealized thermodynamic cycle) describes the functioning of a typical spark ignition piston engine. Different types of arrangement of cylinders in a piston engine are- 1. V engine 2. Radial engine 3. In-line engine 4. Horizontally opposed engine A Stroke is defined as the linear distance that the piston moves in the cylinder. When the piston is at the top of the stroke it is said to be at Top Dead Centre (TDC), and when at the bottom of the stroke Bottom Dead Centre (BDC). The internal diameter of the cylinder is called the Bore. The four strokes of an Otto cycle are: a) Induction b) Compression c) Power d) Exhaust ➢ Induction stroke The momentum of the mixture increases as the induction stroke proceeds, and towards the end of the stroke, it is such that the gases will continue to flow into the cylinder even though the piston has passed BDC and is moving upwards slightly. ➢ Compression stroke As the piston moves upwards, the inlet valve closes and the gas is compressed. By squeezing the gas into a smaller space the pressure that it will exert when burnt is proportionally increased. ➢ Power stroke Before the piston reaches TDC on the compression stroke the gas is ignited by a spark, the momentum of the moving parts carrying the piston past the TDC whilst the flame is spreading. ➢ Exhaust stroke Finally the piston moves upward forcing the remaining gases out of the cylinder. The exhaust valve is left open after TDC to permit the gases to scavenge the cylinder as completely as possible by their momentum. Fixed Pitch Propeller ➢ A propeller converts shaft power from the engine into thrust. It does this by accelerating a mass of air rearwards. Thrust from the propeller is equal to the mass of air accelerated rearwards multiplied by the acceleration given to it. A mass is accelerated rearwards and the equal and opposite reaction drives the aircraft forwards. ➢ Fixed pitch propellers have their pitch or blade angle fixed. The blade angle or pitch can’t be changed during the course of flight. ➢ At a constant RPM, increasing TAS decreases the angle of attack of a fixed propeller. ➢ At a constant TAS, Increasing RPM increases the angle of attack of the propeller. ➢ Aerodynamic forces acting on the propeller• Thrust- A component of force at right angles to the plane of rotation. The thrust force will vary along the length of each blade, reducing at the tip where the pressures equalize and towards the root where the rotational velocity is low. Thrust will cause a bending moment on each blade, tending to bend the tip forward. (Equal and opposite reaction to “throwing” air backwards). • Torque- Torque is the equal and opposite reaction to the propeller being rotated, which generates a turning moment about the aircraft longitudinal axis. Propeller torque also gives a bending moment to the blades, but in the opposite direction to the plane of rotation. • Centrifugal Twisting Moment (CTM) - Components ‘A’ and ‘B’, of the centrifugal force acting on the blade, produce a moment around the pitch change axis which tends to ‘fine’ the blade off. • Aerodynamic Twisting Moment (ATM) - Because the blade CP is in front of the pitch change axis, aerodynamic force generates a moment around the pitch change axis acting in the direction of coarse pitch. The ATM partially offsets the CTM during normal engine operations, but the CTM is dominant. However, when the propeller is windmilling, the ATM acts in the same direction as the CTM and will reinforce it. ➢ Disadvantages of Fixed pitch propeller With a fixed pitch propeller being driven by a piston engine, the rpm is dependent on the power setting (throttle position) selected by the pilot and the TAS of the aircraft. It would be possible to overspeed the engine in a dive if the throttle were not backed off (closed). Conversely, with the aircraft stationary on the ground it may not be possible to achieve rated rpm with the throttle fully open.
