Air Pilot’s Manual CAA Recommended JAR - FCL Syllabus & EASA Part-FCL Compliant LAPL & National PPL Syllabus Compliant Includes Question & Answer SectionThe Air Pilot’s Manual Volume 3 Air Navigation ‘Recommended reading’ Civil Aviation Authority POOLEYS Air Pilot PublishingNothing in this manual supersedes any legislation, rules, regulations or procedures contained in any operational document issued by The Stationery Office, the Civil Aviation Authority, the manufacturers of aircraft, engines and systems, or by the operators of aircraft throughout the world. Note that as maps and charts are changed regularly, those extracts reproduced in this book must not be used jor flight planning or flight operations. Jeppesen charts in this manual have been reproduced with permission and are copyrighted by Jeppesen & Co GmbH. Acrad charts in this manual have been reproduced with permission and are copyrighted by Thales Avionics. Copyright © 2013 Pooleys-Air Pilot Publishing, ISBN 1 84336 067 5 First edition published 1987 Second revised edition 1987 Third revised edition published 1997 Fourth edition 1999 Fifth revised edition 2003 Reprinted with amendments 2004 Reprinted with amendments 2005 Reprinted revisions and colour illustrations 2007 Reprinted with amendments 2008, Sixth Edition 2010 Reprinted with amendments 2011 Reprinted with revisions 2013 Alll rights reserved. No part of this book may be reproduced or transmitted in any form by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without permission from the publisher in writing, Origination by Pooleys-Air Pilot Publishing Limited. Printed in England by Portland Print, Kettering NN16 8UN. Published by Pooleys-Air Pilot Publishing Ltd Highdown House Shoreham Airport ‘West Sussex BN43 5PB England Tel: +44(0)208 207 3749 Web: www.pooleys.com e-mail: sales@pooleys.comThe Air Pilot’s Manual Volume 3 Contents Introduction Section One - Basic Navigation Theory The Pilot/Navigator Speed Direction Wind Side of the Navigation Computer Calculator Side of the Navigation Computer Vertical Navigation Time The Earth Aeronautical Charts of od Be be ee Section Two - Flight Planning 10. Introduction to Flight Planning 11. Pre-Flight Briefing 12. Route Selection and Chart Preparation 13. Compiling a Flight Log 44. The Flight Plan Form Section Three ~ En-Route Navigation 15. En-Route Navigation Techniques 16. Navigation In Remote Areas 17. Entry/Exit Lanes and Low-Level Routes vii 3t 49 at 103 131 149 163 197 203 215 221 239 245 291 297Section Four ~ En-Route Navigation with Radio Navaids areas 18. Introduction to Radio Navigation Aids 305 the en route ravigtion requireents 19: Rear 307 Crthe JARCFCL syllabus. 20. DME 323 Refer to the notes on 21. The NDB and the ADF 329 age 304, Section Four 22. The Relative Bearing Indicator (RBI) 345 Nguoi Pr wang 23. The Radio Magnetic Indicator (RMI) 361 syllabus nor tothe LAPL 24. The VOR 379 _Splabus. 25. VHF Direction Finding (VDF) ant 26. Introduction to RNAV and GPS 423 Appendix 1 The Navigation Skill Test 429 Appendix 2 Planning the Climb 435 Exercises and Answers Section One Exercises 445 Section Two Exercises 465 Section Three Exercises 469 Section Four Exercises 471 Section One Answers 479 Section Two Answers 486 Section Three Answers 493 Section Four Answers 495 Index 497Editorial Team Dorothy Saul-Pooley LLB(Hons) FRAeS Dorothy holds an ATPL (A) and a CPL (H), and is both an instructor and examiner on aeroplanes and an instructor on helicopters. She is Head of Training for a school dedicated to running Flight Instructor courses at Shoreham. She is also a CAA Flight Instructor Examiner. In addition, having qualified as a solicitor in 1982, Dorothy acted for many years as a consultant specialising in aviation and insurance liability issues, and has lectured widely on air law and insurance issues. This highly unusual combination of qualifications led to her appointment as Honorary Solicitor to the Guild of Air Pilots and Navigators (GAPAN). Dorothy isa Fellow of the Royal Aeronautical Society, past Chairman of both the GAPAN Instructor Committee and the Education & Training Committee, as well as serving as a Warden on their Court. She is currently Master Elect and will be installed as Master in March 2014. In 2003 she was awarded the Jean Lennox Bird Trophy for her contribution to aviation and support of Women in Aviation and the BWPA (British Women Pilots Association). In 2013 Dorothy was awarded the prestigious Master Air Pilot Certificate by GAPAN. A regular contributor to seminars and conferences, Dorothy is the author and editor of a number of flying training books and has published articles in legal and insurance journals. David Robson David is a career aviator having been nurtured on balsa wood, dope and tissue paper. He won an ATC Flying Scholarship and made his first solo flight in a Chipmunk at Biggin Hill shortly after his seventeenth birthday. His first job was as a junior draughtsman at the Commonwealth Aircraft Corporation in Melbourne. He joined the RAAF in 1965 and served for 21 years as a fighter pilot and test pilot. He flew over 1,000 hours in Mirages and 500 on Sabres. He completed the Empire Test Pilot’s course at Boscombe Down in 1972, flying everything from gliders, the magnificent Hunter, to Lightnings and Argosies. He completed a tour in Vietnam as a forward air controller in support of the First Australian Task Force. After retiring from the Air Force, he became a civilian instructor and lecturer. During 1986-88 he was editor of the Aviation Safety Digest, which won the Flight Safety Foundation’s international award. He was awarded the Australian Aviation Safety Foundation’s Certificate of Air Safety for 1998. He loves aeroplanes, aerobatics and instructing and still dreams of one day, flying a Spitfire.vi Acknowledgements The Civil Aviation Authority; ICAO; Cessna, Piper, and Gulfstream American for technical material; Daljeet Gill, Peter Godwin, Capt. R.W. K. Snell, Lotti Skeen and Dan Robertson; and the many other instructors and students whose comments have helped to improve this manual. A Condensed History of the Air Pilot Manuals For 25 years the Air Pilot Manuals have led the academic training of pilots in the United Kingdom and in many countries around the world. I first met Trevor Thom, a professional pilot and natural teacher, in Melbourne during a visit to Australia in January 1985. He already had his series of PPL Manuals for the Australian market and I asked him to produce a series for the New Zealand market where we had a small aviation business. Having completed this task, Trevor immediately began writing the first of the Air Pilot Manuals for the United Kingdom market and this project began in eamest on 5th December 1985. Both Trevor Thom and Robert Johnson commenced the task in my office at Feldon. By the end of the following year, all four volumes were complete and were published in February 1987. By the end of that year, we estimated that 95% of all the UK Flying Schools were using our manuals. Volumes 5, 6 and 7 followed, so completing the full series. Unfortunately, Trevor Thom had a serious accident at home which prevented him from continuing with the editing of the manuals. His rights were eventually sold to David Robson, another experienced pilot and natural teacher, who progressively improved the drawings and brought colour into the manuals for the first time. Over the years there have been many assistant editors, in particular Peter Godwin, whose help | first asked for in the very early days with Trevor Thom and which continued until quite recently. The rights in the Air Pilot Manuals are now vested with the Pooley family and they continue to be edited and published from our offices and the Flying Instructor School at Shoreham Airport. The Air Pilot Manuals have an outstanding reputation for accuracy and are continuously updated. They are recommended CAA reading material and are referred to extensively in the CAA examination answer booklet. Robert Pooley CSt] FRIN FRAeSUnderstanding makes for remembering vil Introduction lume 3 of The Air Pilot's Manual — Air Navigation — presents V this important area of training for the Private Pilot’s Licence in a logical sequence of theory, preparation and performance. The Cockpit is a Difficult Environment in which to Learn As with the other volumes of The Air Pilot’s Manual, in Air Navigation we have avoided the presentation offacts only’. A thorough understanding of the principles will enable you to gain maximum benefit from your actual navigation exercise flights. This approach will enable you to become a competent pilot/ navigator and will also help to minimise your flight training hours. (It does, however, mean that our book is a little longer than it could be if the aim was only to cram in facts without a reasonable understanding.) In determining the order in which the information is presented, care has been taken to keep things as logical and practical as possible. Consequently, in the first section — Basic Navigation Theory — the simpler, more practical topics of Speed, Direction and Using the Navigation Computer come first, to give you the feel of practical operations, before some more involved subjects: Vertical Navigation, The Earth and Aeronautical Charts. Operational Decisions Navigation of an aeroplane consists mainly of making common sense operational decisions. These decisions are based on knowledge and experience. Very few are difficult to make — most being logical and simple — but occasionally there are difficult decisions (both on the ground and in flight) to be made. These are the ones for which we must prepare for. ‘We have adopted a professional approach right from the start, whether your ultimate aim is to be a private pilot or to go on and make aviation your career. Operational decisions will often have to be taken well away fiom your home base, and to a large extent you will be on your own. They fall into two categories: + those made on the ground during pre-flight planning; and * in-flight operational decisions. Many decisions are so simple and ‘second nature’ that you don’t realise you are making them. Others require a calm, cool but quick assessment, followed by a decision and action. Proceeding into an area of poor visibility could fall into this category.vili The aeroplane will not stand still while you decide what to do in difficult in-flight situations. You cannot just pull over to the side of the road and study your maps. Good pre-flight planning, with many operational decisions taken on the ground — and alternative courses of action considered in the event of in-flight problems occurring — takes a lot of pressure off the pilot/navigator. The Navigation Computer As a pilot/navigator you will become adept at estimating angles, distances, time intervals, fuel consumption, and so on. The art of estimating is an important skill to develop. It is also important that you can calculate these various quantities easily and accurately. To achieve this you will use a navigation computer. It is a simple device (looks complicated but isn’t) that allows us to carry out almost every navigation calculation with speed and accuracy. Electronic navigation computers are available, but we suggest you steer away from them, at least initially, because they do not encourage the pilot/navigator to visualise each situation — an important ability to develop. Once you are adept at the various computing problems involved in air navigation, you might decide to ‘go electronic’. Beware of becoming over-reliant on electronic computers because you are not permitted to use them in the examination. The basic concept of the slide navigation computer dates back to early navigation days. The modern version is an essential piece of equipment for a pilot/navigator. The slide navigation computer has two sides: + a wind side, which enables solution of triangle of velocities problems for flight-planning and en route navigation; and * a calculator side (the main component of which is a circular slide-rule on the outer scales), used to perform the simple arithmetical calculations involved in flight operations, e.g. distance, speed and time; conversion of units; fuel quantities and consumption; true airspeed. Two chapters in the first section describe using the navigation computer ~ one chapter for each side. Although it may appear a little complicated at first, working through the examples and illustrations we have set out will make using the computer logical and simple.gn ai “a wen idee *s fugit EoUey ix ED nema 200%1) CORRECTIONS, Tok FACTORS TOR TAS ‘CALIBNATED AW SL 1 Pibieg hig Hl The wind and calculator sides of a navigation computer The Theory Examination Navigation is part of one of the theory examinations for the UK Private Pilot's Licence (PPL), which you will sit at your flying school. Prior to this you should be achieving considerable success in completing the Exercises at the back of the book. They are mentioned at the relevant places in each chapter, and in this volume some chapters have exercises interspersed through the text to give you practice on a particular aspect of the chapter before moving on. The Exercises form an important part of the course and we recommend that you work through them carefally. This manual is more than just a text to allow you to pass the examination, though this is ‘one of its aims. It is designed to remain as a reference text on your shelf for as long as you fly. In places we have included more information than is required for the Air Navigation examination section. For example,x Appendix 2 shows you how to plan a climb ~ something which, although not required of you in the PPL examination, will enable you to plan longer, higher altitude flights in the future. The En route Navigation Section (PPL Skill Test) This is the province of your flying instructor. The test is carried out at the completion of your flying training and is part of the PPL Skill Test (although with the agreement of your examiner it may be flown as a separate section.) It is designed to assess your ability as a pilot/navigator. This manual, and your navigation cross- country training, will prepare you fully for the Navigation element of the PPL Skill Test. Private Pilot Licences This edition covers the material contained in the JAR-FCL and NPPL training syllabus as well as that required by the new European Part-FCL and Light Aircraft Pilot Licence (LAPL) syllabus. Students should follow one syllabus only. Section Four of this manual is only required for the JAR-FCL or Part-FCL Licence, not for the NPPL or LAPL, although the theoretical knowledge examination may include some of this material for any of the licences. Operational Information For safe flight operations it is essential that all pilots refer to current operational information. This basically involves using latest issues of aeronautical charts, and amended flight information publications, circulars and NOTAM (Notices to Airmen). In the UK, the primary source of operational information is the UK Aeronautical Information Publication (AIP), a large, frequently amended manual produced to an international standard by the Civil Aviation Authority. Your flying school and Air Traffic Services (ATS) units should have amended copies of the UK AIP available for reference, although these days they are often available ona CD rom, or directly on the internet from the AIS website: www.ais.org.uk. As the AIP is a formidable and bulky set of documents for a PPL holder (because the majority covers airline- type instrument flight procedures), there is also available a conveniently sized publication known as Pooley’s Flight Guide, which is revised regularly. You will find references to both Pooley’s Flight Guide and the UK AIP throughout The Air Pilot's Manual. Note that these references are no substitute for referring to current, amended documents. If you are ever in any doubt about operational information, in Pooley’s Flight Guide or the UK AIP, refer to an amended copy of the AIP and current air legislation documents; and always check the latest AIRACs (which detail AIP updates), AIP Supplements and Aeronautical Information Circulars (AICs) and NOTAM prior to flight.Section One Basic Navigation Theory Chapter 1 The Pilot/Navigator Chapter 2 Speed Chapter 3 Direction Chapter 4 Wind Side of the Navigation Computer Chapter 5 Calculator Side of the Navigation Computer Chapter 6 Vertical Navigation Chapter 7 Time Chapter 8 The Earth Chapter 9 Aeronautical Charts 31 49 81 103 131 149 163BASIC NAVIGATION THEORYChapter 1 ‘Sound preparation is the basis for a confident navigation exercise. The Pilot/Navigator Air Navigation Il air navigation involves basic principles that apply to all aeroplanes, from the simplest trainer to the most sophisticated passenger jets. These basic principles are discussed in this manual. Since The Air Pilot’s Manual is a training programme for the Private Pilot's Licence (PPL), we will concentrate on accurate navigation of a light aircraft, flown by a single pilot, in visual conditions. PPL holders, when flying cross-country, act as pilot, navigator and radio operator. They must: «primarily fly the aeroplane safely and accurately; * navigate correctly; * operate the radio and attend to other duties in the cockpit. In short, they must ‘aviate, navigate and communicate’. To conduct a cross-country flight efficiently, navigation tasks must be coordinated with (and not interfere with) the smooth flying of the aeroplane. It is most important that the pilot/ navigator clearly understands the basic principles underlying navigation so that correct techniques and practices can be applied quickly and accurately without causing distraction ot apprehension. Prepare Soundly Being properly prepared prior to a cross-country flight is essential if it is to be successful. Always flight plan meticulously. This establishes an accurate base against which you can measure your in-flight navigation performance. Pre-flight consideration should be given to navigation items such as: * the serviceability of your watch or aircraft clock — time is vital to accurate navigation; + the contents of your ‘nav bag’ — pencils, navigation computer, protractor and scale (or a plotter), suitable maps and charts, and relevant flight information publications; + the preparation of the appropriate maps and charts; * the desired route; * the terrain en route; + the airspace en route (uncontrolled, controlled, special rules advisory etc.); + the suitability of the destination and any alternate acrodromes4 BASIC NAVIGATION THEORY + the forecast weather en route and at the destination and alternate aerodromes (plus any actual reports that are available); + the calculation of accurate headings and groundspeeds; * consideration of fuel consumption, and accurate fuel planning. Tt sounds like a lot, but each item considered individually is simple to understand. After considering them one by one in separate chapters, we will put them all together and see how they fit into a normal cross-country flight. In Flight, Fly Accurate Headings Once the aeroplane is in flight, flying a reasonably accurate heading (which involves reference to both the direction indicator and outside cues) is essential if the aeroplane is to track towards the desired destination. Maintaining cruise airspeed, and comparing your progress and times of arrival at various fixes with those estimated at the flight-planning stage, will normally ensure a pleasant and drama-free joumey. Navigation Tasks are Additional to Flying the aeroplane Our objective in this volume of The Air Pilot’s Manual is to show you navigation techniques that will not increase your workload in the cockpit to an unacceptable degree, but will still allow time to fix your position and navigate the aeroplane safely to your desired destination. We make the assumption that you already know how to fly the aeroplane; the idea here is to add to these flying skills the basic principles of air navigation, Other aspects that have a bearing on the conduct of a cross-country flight are covered in their own sections (for instance, airspace, radio procedures and meteorology in Vol. 2). The Earth All navigation is done with reference to the surface of the earth — starting from the elementary exercise of ‘navigating’ the aeroplane around the circuit during your initial training (which requires visual reference to ground features such as the runway and points ahead of the aeroplane for tracking) and progressing to the large passenger jets using sophisticated instrument navigation techniques to cover vast distances around the earth. Direction on Earth Direction is the angular position of one point to another without reference to the distance between them. It is expressed as the angular difference from a specified reference direction. In air navigation this reference direction is either: * north (for fue or magnetic bearings); or + the heading (or the nose) of the aircraft (for relative bearings).1 — The Pilot/Navigator 7 The simplest means of describing direction is to consider a circle laid flat and then divided into 360 units, called degrees (°). These units are numbered clockwise from 000 in the reference directior all the way around the circle to 360. North ‘000 360 300 060 West 270 090 East 240 120 210 150 180 South 1 Feure 1-1 To measure direction, a circle is divided into 360 degrees (°) Itis usual to refer to direction as a three-figure group to prevent any misunderstanding in the transmission of messages. For example, north is referred to as 360. East is referred to as 090, south-west as 225. Posi non Earth The main method of specifying the position of a place on the surface of the earth is the latitude and longitude system. ‘This involves covering the surface of a reduced earth with an evenly spaced graticule of lines — north-south lines joining the North and South Poles, and east-west lines parallel with the equator. The north-south lines are known as meridians of longitude and the east-west lines are called parallels of latitude. North Pole Parallels North Pole of latitude South Pole ‘South Pole Prime meridian Cross-section of Earth Viewed irom above North Pole Figure 1-2 Position on earth is usually specified with reference to meridians of longitude and parallels of latitude6 Basic NAVIGATION THEORY The position of any place on the surface of the earth can then be specified with reference to the equator and a datunt (or prime) meridian of longitude. The universal base longitude used throughout the world — longitude 0° — is the meridian drawn (north-south) through Greenwich, near London, known as the prime meridian. Distance on Earth The separation of two points on earth is called distance and is expressed as the length of the shortest line joining them. The standard unit of distance in navigation is the nautical 1 nm = 1,852 metres (1.852 km). (nm). The nautical mile is related to the size of the earth in that it is payucalmie equals the length of 1 minute of latitude. It is slightly longer than the 4 minute of latitude familiar statute mile; 1 nautical mile (am) measures 6,076 ft compared to 5,280 ft in the statute mile (sm). One minute of latitude is measured down the side of a chart, i.e. along a meridian of longitude, which is a great circle. A great circle is one whose centre lies at the centre of the earth. All meridians of longitude and the equator are great circles. Thus 1 minute of are of any great circle will be 1 nautical mile. This is explained in more detail in Chapter 8, The Earth eottattude | 5 Great circle | 1 | | | | | | 53°30°N: d> irate asco 1 sondot| ieuteeciee Earth Earth TH Figure 1-3 A great circle, and 1° of latitude on the earth and on a chart There are 360 degrees in a circle and each degree has 60 minutes, ie. a circle has (360 x 60) = 21,600 minutes — which makes the circumference of the earth approximately 21,600 nautical miles Ifan aeroplane travels 1 nautical mile through an air mass, we refer to this as 1 air nautical mile (anm). As well as the aeroplane moving through the air mass, the air mass will be moving across the ground (in the form of a ‘blowing’ wind) and will carry the aeroplane along with it. The wind velocity adds an extra effect to1 — The Pilot/Navigator 7 the passage of the aeroplane over the ground. If an aeroplane travels 1 nautical mile over ground or water, we refer to this as 1 ground nautical mile (gnm). NOTE While navigation distances are measured in nautical miles, other shorter horizontal distances, such as runway length or horizontal distance from cloud, may be referred to in metres. In air navigation we are concerned not only with horizontal navigation but also with vertical navigation (see Chapter 6). The traditional and standard unit for vertical distance, or height, is the foot (fi). Speed Speed is the rate at which distance is covered; in other words, speed is distance per unit time. The standard unit for speed is the knot (Ke). 1 knot =1 nautical mile per hour. Direction and Speed Combined An aeroplane flies in the medium of air. Its motion relative to the air mass is specified by its: * direction (known as heading); and + speed through the air mass (true airspeed). HEADING (HDG). When flown in balance (as it normally is) the aeroplane will travel through the air in the direction in which it is heading, If the aeroplane is heading east (090), then its passage relative to the air mass will be easterly (090) also. TRUE AIRSPEED (TAS). This is the actual speed of the aeroplane relative to the air mass. True airspeed is normally abbreviated to TAS, but occasionally to V when used in aerodynamic formulae. (See Principles of Flight in Vol. 4 of The Air Pilot's Manual.) When considered together, HDG/TAS constitute a vector quantity, which requires both magnitude (in this case TAS) and direction (here HDG) to be completely specified. HDG/TAS is the velocity (direction and speed) of the aeroplane through the air. The HDGITAS vector fully describes the motion of the aeroplane relative to the air mass. HDGITAS is symbolised by a single-headed arrow ———>—— ; the direction of the arrow indicates the direction of movement along the vector line.8 BASIC NAVIGATION THEORY Heading 330° at 80 KTAS Heading 220° at 120 KTAS 4 I Figure 1-4 Examples of the HDGITAS vector An Air Mass can Move Relative to the Ground (a Wind can ‘Blow’) The general movement of air relative to the ground is called wind velocity and is abbreviated to W/V. Like HDG/TAS, W/V isa vector quantity because both direction and magnitude are specified. By convention, the wind direction is expressed as the direction fiom which it is blowing. For example, a northerly wind blows from the north towards the south. W/V is symbolised by a triple- headed arrow ——>3>— . The WIV vector fully describes the horizontal motion of the air mass relative to the earth's surface. —»>—_ gp A vs uissonng —— Asaueny vin of 30 knots, from 030° at 10 knots, of 15 knots, i.e. 270/30 i.e. 030/10 Le. 180/15, Ml Figue 1-5 Examples of the wind vector With a W/V of 230/20, the air mass will be moving relative to the earth’s surface from a direction of 230° at a rate of 20 nautical miles per hour Ina 6 minute period, for example, the air mass will have moved 2nm (6 minute = '/ hour; '/w of 20 am = 2 nm) from a direction of 230°, and therefore towards (230 — 180) = 050°. Heading 180° at 60 KTAS Awind blowing from 210° at 20 knots, ie. 210/201 — The Pilot/Navigator Final position of air mass Initial position} of air mass | Ml Figue 1-6 A wind of 230/20 The motion of the aeroplane relative to the surface of the earth is made up of two velocities: + the aeroplane moving relative to the air mass (HDG/TAS); and + the air mass moving relative to the surface of the earth (W/V). Adding these two together gives the resultant vector of: + the aeroplane moving relative to the surface of the earth. This is the track and groundspeed (TR/GS), which is symbolised by a double-headed arrow ——>>—— . o c a wn — HDG/TAS TRIGS TRIGS is symbolised by a double-headed arrow I J A Figure 1-7 HDGITAS + WIV = TRIGS An aeroplane flying through an air mass is in a similar situation to you swimming across a fast flowing river. Ifyou dive in at A and head off through the water in the direction of B, the current will carry you downstream towards C. To an observer sitting overhead in the branch ofa tree, you will appear to be swimming a little bit ‘sideways’ as you get swept downstream, even though in fact you are swimming straight through the water.10 Basic NAVIGATION THEORY In the same way, it is common to look up and see an aeroplane flying somewhat ‘sideways’ in strong wind situations. Of course the aeroplane is not actually flying sideways through the air, rather it is flying straight ahead relative to the air mass (HDG/TAS). It is wind velocity (W/V) which, when added to the aeroplane’s motion through the air (HDG/TAS), gives it the resultant motion over the ground (track/groundspeed). To fly from A to C in the above situation, the pilot must fly on a HDG of A-B through the air, ic. maintain the nose of the aeroplane in a direction parallel to A~B. The wind will have the effect of B-C.The combined effect of these, known as the resultant, will give the aeroplane a track over the ground of A~C. The TR/GS vector fully describes the motion of the aeroplane relative to the earth's surface. The Triangle of Velocities The two velocities: + HDG/TAS: the aeroplane moving through the air mass; and + W/V: the air mass moving over the ground; when added together as vectors, give the resultant: + TRVGS (track/groundspeed) — the aeroplane moving over the ground. These three vectors form the triangle of velocities. It is a pictorial representation of the vector addition: HDG/TAS + W/V = TR/GS. ive. the combined effect of HDG/TAS plus W/V will give the resultant TR/GS (Figure 1-8). ZL =f HDG/TAS free “TS Drift angle = MH Figure 1-8 The triangle Ml Figure 1-9 Drift is the angle of velocities between heading and track1 ‘The Pilot!Navigator We add the two vectors for HDG/TAS and W/V ‘head to tail i.e. starting from A, the head of the HDG/TAS vector at B is th starting point for the tail of the W/V vector which then ends at C. The resultant effect of the two combined is the TR/GS vecto starting at A and finishing at C. This is the path that the aeroplan would fly over the ground. The angle between the HDG and th track (TR) is called the drift angle (Figure 1-9). You may have already seen this triangle of velocities illustrate: on a navigation computer, as in Figure 1-10 ao Ocpylge Destination 3 Phe an en Wind effect v @eor Poe udston ve f 2 —o ¢ DARRELL ee ‘OAIFFELD} (Track Ba Heading TRIGS ete aph '& state St Tu i LSTREE ‘SAMPLE ONLY Not fo be used for operational purposes F Departure UN AREY 450 lH Figure 1-10 The triangle of velocities laid on the wind side of a navigation computer Do notbe put off by the apparently complicated appearance the navigation computer. It is a marvellous device designed t make navigation tasks easier. Chapter 4 describes using the win side of the computer in detail, so it will become quite clear. At the flight planning stage: + you will know the desired track (track required); and + will obtain a forecast wind velocity.12 BASIC NAVIGATION THEORY Using the known true airspeed, you will be able to calculate: + the heading required to ‘make good’ the desired track; and + the expected groundspeed. Later on during the flight you may find that, even though you have flown the HDG/TAS accurately, your actual track made good (TMG) over the ground differs from your desired track; in other words there is a track error. It is most likely to be caused by the actual wind being different from the forecast wind that you used at the flight planning stage. You will then have to make some adjustments to the HDG to carry out the navigation task of rejoining your desired track and continuing to the destination. This is what air navigation is all about. The essential principles are simple and have now been covered. All we have to do is expand on them in the following chapters and combine them into practical navigation operations. Summary of Terminology HpaTas: Heading (HDG) is the actual heading of the aeroplane in degrees steered by the pilot. It may be related to true north, magnetic north or compass north. True airspeed (TAS) is the actual speed of the aeroplane through the air. It will differ significantly from the airspeed indicated on the airspeed indicator (the indicated airspeed) due to the air being less dense the higher the aeroplane flies. The pilot will need to complete a small calculation to convert indicated airspeed (IAS) to true airspeed (TAS) when flying at altitude. The normal unit for airspeed is the knot. IAS is useful for aerodynamics, but TAS is necessary for navigation. The normal unit of distance for navigation is the nautical mile (nm) and if it is distance relative to the air, we call it an air nautical mile (anm). tris: Track (TR) is the path of the aeroplane over the surface of the earth, and is usually expressed in degrees true or magnetic. Groundspeed (GS) is the actual speed of the aeroplane over the ground and is measured in knots. A GS of 120 kt means that 120 ground nautical miles would be covered in 1 hour at that GS. DRIFT is the difference between the HDG steered by the pilot and the track of the aeroplane over the ground. The wind blows the aeroplane from its HDG/TAS through the air onto its TR/GS over the earth’s surface. Drift is measured from the HDG (the nose of the aeroplane) to the TR, and is specified in degrees left (port) of HDG or right (starboard) of HDG.The Plot/Novigator Drift angle 410° right I Figure 1-11 Drift is the ongle between heading and track wiv: Wind direction is expressed in degrees trve or magnetic an is the direction from which the wind is blowing. Wind speed measured in knots (kt). 1 kt = 1 nm per hour. TRACK ERROR: The actual track made good (TMG) over th ground will often differ from the desired track. The angule difference between the desired track and the TMG is called trac error and is specified in degrees left (port) or right (starboard) c the desired track. o” Desired TR FT Actual TR (TMG) Track error 5° right @ figure 1-12 Track error is the angle between desired track and the track made good (TMG) NOTE Track error is totally different from drifi. LATITUDE: The distance of a place north or south from th equator, measured in degrees. LONGITUDE: The distance of a place from the prime meridian (0° through Greenwich, also measured in degrees. NAUTICAL MILE: The length of 1 minute of latitude measure along a meridian, ie. down the side of a chart. KNOT: Unit of speed equal to 1 nautical mile per hour. GREAT CIRCLE: Intersection of the earth's surface and a plan passing through the earth’s centre. Now complete Exercises 1- The Pilot/Navigator. Exercises and Answers are at the back of the book.14 Basic NAVIGATION THEORYChapter 2 Speed Airspeed Age: understanding of the factors involved in airspeed i important if you are to become a competent pilot, navigator. The true airspeed (TAS) of an aircraft is its rate 0 progress or speed through the air mass in which it is flying Whether the air mass is moving over the ground or is stationary is irrelevant to the true airspeed. TAS is simply the speed of th« aircraft through the air. In contrast, a hot-air balloon or a cloud has no horizonta driving force of its own and so just hangs in the air. This means the TAS ofa balloon or a cloud is zero because it is not moving relativ. to the air mass. Figure 2.1 An air mass can be stationary or move as If the air mass is moving relative to the ground (ie. the winc velocity is other than zero), then the balloon or cloud will be carried by the air mass across the ground. Being static in the ai mass, the balloon or the cloud could theoretically be used as : point against which to measure the true airspeed (TAS) of ar aircraft. In other words, an aircraft will fly past a balloon, or : cloud, at its true airspeed.16 Basic NAVIGATION THEORY The actual speed of an aircraft relative to the ground is called the groundspeed (GS). The resultant groundspeed is a combination of: + the true airspeed (TAS — the movement of the aircraft relative to the air mass); and + the wind velocity (W/V — the movement of the air mass relative to the ground). This is familiar from the ‘triangle of velocities’ in Chapter 1. 2 2 ; wi TAS : i 6s MH Figure 2-2 The groundspeed is the resultant of the true airspeed (TAS) and the wind velocity (WIV) At this stage we are only interested in airspeed — the speed of the aircraft through the air, (Groundspeed comes later in the book.) International Standard Atmosphere (ISA) A standard atmosphere has been defined as a ‘measuring stick” against which we can compare the actual atmosphere that exists at a given place on a given day. The standard atmosphere has: + A standard mean sea level (MSL) pressure of 1013.25 hectopascals (hPa), which decreases by about 1 hPa for each 30 ft of altitude gained. For practical purposes, we use 1013 hPa. + A standard MSL temperature of + 15°C, which decreases by about 2°C for each 1,000 ft of altitude gained. + The ISA MSL air density is 1,225 gm/cubic metre, and this also decreases as altitude is gained. NOTE The hectopascal (hPa), a standard unit of pressure for aviation, equivalent to millibars, has been adopted in many countries, Because 1 mb = 1 hPa, only the name change is significant. The UK recently adopted the hPa but many places still use millibars (mb) and the USA still uses inches and you will see hPa in the Republic of Ireland and in Europe.2 -Speed 1 Pressure ‘Temperature Density decrease decrease decreases thPaper 30 ft 2°C por 1,000 ft wit! (approximately) (approximately) altitude [Mean sea level] |_| _ [Standard pressure] __ [Standard temperature ‘Standard density 1013 hPa +15°C (+59°F) 1,225 g/m? I Figure 2-3 The International Standard Atmosphere (ISA) Speed Measurement To measure the speed of an aircraft is a little more complicate: than you might expect. The basic instrument used is the airspee: indicator (ASI) which is a pressure-operated instrument. Th airspeed displayed is given the logical name indicated airspee: (IAS). Due to the nature of the atmosphere — in which air pressur and air density decrease with altitude — and the design of th airspeed indicator, the indicated airspeed (IAS) is usually less tha the true airspeed (TAS). I Figure 2-4 Airspeed indicator with a TAS correction scale18 BASIC NAVIGATION THEORY ‘The indicated airspeed shown on the airspeed indicator in the cockpit and the true airspeed of the aeroplane through the air will only be the same value when International Standard Atmosphere mean sea level (ISA MSL) conditions exist. Such conditions are usually not experienced In conditions other than ISA MSL, pilots must make simple calculations (either mentally or by navigation computer) to convert the IAS they read on the airspeed indicator to the TAS needed for navigation. The fact that the word airspeed has a number of meanings in aviation may be confusing at first but you must understand the differences. * Performance of the aeroplane is related to indicated airspeed (IAS) (i.e. whether the aircraft will stall or not, its rate of climb performance, lift/drag ratio etc.), and is a function of TAS. Indicated airspeed is related to dynamic pressure. + Navigation and flight planning depend on true airspeed (TAS), wind velocity (W/V) and groundspeed (GS). True airspeed is the actual speed of the aeroplane through the air. To understand the difference between the two basic airspeeds: indicated airspeed (IAS), and true airspeed (TAS), we need to consider briefly certain properties of the atmosphere and the principles of fluid flow. Static Pressure Static pressure at any point in the atmosphere is exerted equally in all directions. It is a result of the weight of all the molecules composing the air above that point. At this very moment, static pressure of the atmosphere is being exerted at all points on the skin of your hand Low static pressure at altitude Static pressure Static pressure acts ‘equally in all directions Static vent Partially evacuated High static pressure . He capsule at mean sea level I Figure 2-5 Static pressure2- Speed 19 As its name implies, static pressure does not involve any motion of the body relative to the air. Dynamic Pressure If you hold your hand up in a strong wind or out of the window ofa moving car, then an extra wind pressure, or ‘moving pressure’, is felt due to the air striking your hand. This extra pressure, over and above the static pressure which is always present, is called dynamic pressure, or pressure due to relative movement. It is felt by a body that is moving relative to the air, i.e, it could be moving through the air, or the air could be flowing past it. Relative airflow HH Figure 2.6 Dynamic pressure Just how strong dynamic pressure is depends on a number of things, the two main ones being: 1, The speed of the body relative to the air. The faster the car drives or the faster the wind blows, then the stronger the extra dynamic pressure that you feel on your hand. This is because of the greater number of air molecules that strike it per second. 40 knots, hig) dynamic pressure MH Figue 2-7 Dynamic pressure increases with airspeed 2. The density of the air. In outer space, no matter how fast you travelled, you would not feel any dynamic pressure because there are practically no molecules to strike you. In contrast, at sea level, where the atmosphere is densest, your hand would be struck by many molecules per second — certainly many more than in the upper regions of the atmosphere. Even though you might be travelling at the same speed, you will feel a much lower dynamic pressure in the higher levels of the atmosphere, where the air is less dense, than in the lower levels.20 BASIC NAVIGATION THEORY Outer space: no molecules of air strike a moving body High altitude: many molecules of air per second strike a moving body Low altitude: many, many molecules of air per second strike a moving body Ml Figure 28 Air density decreases with altitude So, for an aircraft moving at a constant true airspeed, less dynamic pressure is experienced the higher the altitude. The actual measure of dynamic pressure is written: Dynamic pressure = '/%, x rho x V-squared 2 + tho represents air density, which decreases with altitude. + Vrepresents the speed of the body relative to the air, ive. the true airspeed. (It does not matter whether the body is moving through the air, or the air blowing past the body, or a combination of both — as long as they are moving relative to one another there will be an airspeed and a dynamic pressure.) Total Pressure In the atmosphere some static pressure is always exerted, but only if there is motion of the body relative to the air will any dynamic pressure (due to relative motion) be felt by the surface exposed to the airflow. Thus: Total pressure consists of static pressure plus dynamic pressure.2- Speed 1 Flexible = Diaphragm = Pitot tube Statice | Total pressure (pitot) pressure (dynamic and stalic pressure) Static vent Figure 2-9 Total pressure is measured by a pitot tube Much of this theory about pressure was developed by the Swiss scientist Daniel Bernoulli, and is expressed in Bernoulli's equation, which, in simplified form, is: Static pressure + Dynamicpressure = Total pressure measured by static line Vp tho x V-squared measured by (barometer or altimeter) pitot tube An expression for dynamic pressure can be obtained by sub- tracting the term static pressure from both sides of this equation: Dynamic pressure = total pressure — static pressure Indicated Airspeed (IAS) A measure of dynamic pressure can be found by starting with the total (pitot) pressure, and subtracting the static pressure from it. This is done using a diaphragm with total pressure from the pitot tube fed onto one side, and static pressure from the static line fed onto the other side. ‘The diaphragm in the airspeed indicator (ASI) system positions itself according to the difference between the total pressure and the static pressure, i.e. according to the dynamic pressure. A pointer connected to the diaphragm through a gearing mechanism then moves around the ASI scale as the diaphragm responds to these pressure variations, If we assume that the density of air (rho) remains constant at its mean sea level value (which it does not), the scale around which the pointer moves can be graduated in units of speed. This results in an airspeed indicator that displays the airspeed accurately only under ISA MSL conditions, ie. when the air density is 1,225 grams per cubic metre (the same as at + 15°C, pressure altitude zero). If the air density (rho) is precisely 1,225 gm/cubic metre, then the airspeed indicator will show an indicated airspeed that is the same as the true airspeed of the aeroplane through the air.22 BASIC NAVIGATION THEORY Expandable diaphragm Pitottube __ Airflow Appropriate gearing system Static L ‘Total pressure pressure (pitot pressure) Static vent I Figure 2-10 The flexible diaphragm in the airspeed indicator drives the pointer to display indicated airspeed (IAS) NOTE Airspeed indicators are usually calibrated in knots but you may sce indicators graduated in statute miles per hour, the familiar mph. Indicated airspeed (IAS) is what we read on the airspeed indicator (AS!). Rectified Airspeed (RAS) A particular pitot-static system and its cockpit airspeed indicator (ASI) will experience some small errors. The main two are: 4. Instrument error — resulting from poor design and construction of the AST itself, or from friction within it. 2. Position error — resulting from sensing errors inherent in the position on the aircraft of the static vent and the pitot tube, Their position with respect to the airflow is critical and may lead to somewhat incorrect readings when the airflow pattern is dis turbed at certain airspeeds, angles of attack, or wing flap settings. The pilot can correct the reading, of indicated airspeed shown on the ASI by using a calibration table (found in the Pilot's Operating Handbook for the aeroplane) to obtain a value known as rectified airspeed (RAS) or calibrated airspeed (CAS). NOTE Rectified airspeed is the term commonly used in the United Kingdom, whereas calibrated airspeed is used in the United States of America, many European countries, Australia and New Zealand. Navigation computers may be labelled with either RAS or CAS, or both. The calculated RAS figure is what the ASI would read if the particular airspeed indicator system was perfect. RAS is therefore more accurate than IAS and, if you have taken the trouble to calculate RAS, it should be used in preference to IAS in navigation calculations.2- Speed 23 The instrument and position errors of an airspeed indicator system are usually no more than a few knots and, for our purposes at PPL level, we can generally assume that indicated airspeed (TAS) and rectified airspeed (RAS) are equal. To remind you we will occasionally write [AS (RAS). Now complete Exercises 2 - Spee: By Relating True Airspeed to Indicated Airspeed The aeroplane will rarely be flying in an air mass that has the same density as that under ISA MSL conditions (1,225 gm/cubic metre), the basis of the calibration of the airspeed indicator. Generally an aeroplane flying at altitude will be experiencing an air density significantly less than this, because air density (sho) decreases with altitude. This will also be the case when there is an increase in temperature. The indicated airspeed (even if it has been corrected for instrument and position errors to give rectified airspeed) will need to be further corrected for density error if the pilot is to know the exact speed at which the aeroplane is moving through the air — the true airspeed. Whereas the position and instrument error (if any) will be different for each ASI system, the density error applies equally to all systems because it is a function of the atmospheric conditions at that time and place. Air density varies for two main reasons: 1, Temperature. Cold air is dense, warm air is less dense, so on a warm day an aircraft must travel faster through the air for the same number of molecules per second to strike it, and for the same IAS to be indicated. TAS varying with temperature (for a constant IAS) is one reason why, on a warm day, an aeroplane requires longer take-off and landing distances. The TAS is higher to give you the same IAS, and the IAS is what you ‘fly by’. Colder Warmer Dense air Less dense air IAS 80 Q IAS 80 kt TAS 80 TAS 84 kt ISA MSL +15°C MSL Pressure altitude 0 ft Pressure altitude 0 it 445°C = ISA430 IM Figure 2-11 Constant IAS (RAS): TAS varies with air temperature24 BASIC NAVIGATION THEORY 2, Pressure. The greater the pressure altitude (Le. the lower the air pressure), the fewer the molecules per unit volume. For two aircraft with the same true airspeed (TAS), the higher aircraft will have a lower indicated airspeed (IAS) because it will strike fewer molecules of air per second than the lower aircraft. {ns7m IAS 80 Ee TAS 93 kt TAS 93 Pressure altitude 12,000 ft Pressure altitude 10,000 ft Outside air temperature -5°C Outside air temperature ~5°C Figure 2-12 Same TAS: the aircraft in less dense air has a lower IAS (RAS) Remember that [AS (RAS) is only equal to TAS under ISA MSL (International Standard Atmosphere mean sea level) conditions. At higher altitudes the IAS (or RAS) will be less than the TAS because the aircraft will be flying through the thinner air with an airspeed well in excess of that indicated on the ASI. What Happens When We Climb at a Constant IAS? ‘Asan aeroplane gains altitude, the air density (rho) decreases. If we adopt the usual climb technique of maintaining a constant TAS (a constant dynamic pressure "4 x rho x V-squared’), the decrease in rho is made up by an increase in V (the true airspeed). The higher we climb, when flying at a constant IAS, the greater the TAS. IAS {00 TAS 100 BH figure 2-13 The higher we climb, the greater the TAS for a constant IAS (RAS) Using the Navigation Computer to Find TAS from IAS Finding TAS from IAS is simple with a navigation computer. The principles illustrated here apply to most types available.2- Speed 25 On the calculator side of most navigation computers is an airspeed correction window, which allows us to: + match up the pressure altitude and the air temperature (the main factors determining density); and then * from IAS (or RAS/CAS) on the inner scale, read off TAS on the outer scale. NOTE On many navigation computers the inner scale is labelled RAS or CAS (or IAS) and the outer scale TAS. Check your own. computer. Ensure that you use the Celsius temperature scale, as all tem- peratures in UK meteorology forecasts (and those for most other countries) are given in degrees Celsius (formerly centigrade). EXAMPLE 1 1, Temperature is -10°C at pressure altitude 8,000 ft. 2. RAS (CAS) 115 kt gives TAS 127 kt. JAS (RAS) and ir temperature on the navigation computer As a further example, line up the ISA MSL conditions of +15°C and pressure altitude 0. The computer will then show that under these conditions IAS (inner scale) and TAS (outer scale) are the same. Variation of TAS with Altitude Assume that the recommended climb speed for your aeroplane is 100 kt IAS. Using your navigation computer, see if you can come up with similar answers for the TAS as we have in Figure 2-15, for26 BASIC NAVIGATION THEORY a climb at IAS 100 kt from MSL to 20,000 ft. (Assume standard atmosphere conditions, where temperature decreases by 2°C for each 1,000 ft climbed.) 20,000 ft SPC 100 Ke 137 kt 15,000 ft 15°C 100kt 126 kt 10,000 ft “5° 400kt 117 kt 5,000 fe +5°C 100kt 108 ke 1SA MSL 415°C 100kt 100 kt TAS 100 ———> True airspeed Altitude x 1,000 ft Mean sea level pay I Figure 2-15 IAS 100 kt: TAS increases with altitude NOTE At 5,000 ft, TAS exceeds IAS by about 8%. At 10,000 ft, TAS exceeds IAS by about 17%. These are handy figures to remember for rough mental calculations and also for when experienced pilots are talking about the speeds at which their aeroplanes ‘true-out’. If you are cruising at 5,000 ft with IAS 180 kt showing on the airspeed indicator, then your TAS will be approximately 8% greater (8% of 180 = 14), ive. 194 kt TAS. Now complete Exercises 2 ~ Spee By For a Constant TAS, What IAS is Required? Icis interesting to compare what indicated airspeed will be shown in the cockpit if a constant true airspeed is required at various2- Speed 27 levels. See if you can obtain the same answers as we do for IAS with a constant true airspeed of 200 kt at various pressure alti- tudes. Once again, assume a standard atmosphere to be present. Presureance [Teno [ras ASRas | 20,000 ft -25°C 200 kt 146 kt 15,000 ft 15°C 200 kt 159 kt To fly the same TAS, 70.000 St OK A7Ze. JAS wil decrease with higher ctitudes as the 5,000 fi #5°C 200k: 185k ir density decreases (SA MSL. +1S'C 200 kt 200 kt So, for the same TAS, the greater the pressure altitude, the lower the IAS. The higher an aircraft flies, the more the TAS exceeds the IAS. Variation of TAS with Outside Air Temperature (OAT) Temperature at the one level in the atmosphere will vary from place to place and from time to time. Since temperature affects air density, it will also affect the relationship between IAS and TAS. 4. The mean sea level situation if temperature varies: iene Coca ISAF20=+35°C 100k 104 kt_—_ (less dense air) Pressure GAHIO=+25°C —100kt—« 102 kt se ISA = 415°C 100k —-100kt f BASS WO S00 GAHO=+5% 100k Bt ISA-20 = -5°C 100 ke 96k (more dense air) The less dense the air, the greater the TAS, compared to IAS (RAS). 2. The situation at pressure altitude 10,000 ft, if temperature varies: Tem Conon (AH20=+15°C 100k 121 kt_—_—_ (less dense air) Pressure ISA+10 = +5°C 100 kt 119 kt T , Ee 100k T17ke GA10=-15°C 100K ‘115k 1SA-20=-25°C 100 kt 113 ke (more dense air) True airspeed is important for navigation and flight planning because TAS is the actual speed of the aeroplane through the air mass.28 Basic NAVIGATION THEORY More IAS to TAS Computer Calculations EXAMPLE 2 At FL70, OAT —5°C, IAS (RAS) 105 kt. Find the TAS. Working: Set the pressure altitude 7,000 ft against -5°C OAT in the true airspeed (TAS) window. Then, against RAS 105 kt on the inner scale, read off TAS 115 kt on the outermost scale. TAS is 115 kt. HH Figure 2-16 Example 2 In some situations the required pieces of information are not always given directly, but have to be derived first from other information which is provided. We will take an example from a high flight level to illustrate the widening gap between IAS (RAS) and TAS as an aeroplane climbs. EXAMPLE 3 A turboprop plans on flying at flight level 280 (FL280), where the temperature is forecast to be ISA+10°C. Ifits rectified airspeed (RAS) will be 150 kt, what TAS can be expected? Working: FL280 is pressure altitude 28,000 ft. At FL280, ISA = +15 —(2 x 28) = +15-56 = -41°C soISAH10 = —41+ 10 = 31°C2- Speed 29 In the computer airspeed window, set pressure altitude 28,000 against OAT -31. Against RAS 150 kt, read off TAS 240 kt on the outer scale. Finding the Required IAS to Achieve a Particular TAS The usual in-flight problem is to determine the TAS from the indicated airspeed read off the ASI. Sometimes, however, you need to be able to work these problems in reverse, say to achieve a certain desired TAS or GS for flight planning purposes, when you will start with these and work back to find the IAS (RAS/ CAS) necessary to achieve this. EXAMPLE 4 Cruising at FL100 and temperature ISA~10, what is the required RAS (CAS) to give you a true airspeed of 200 kt? Working: Pressure altitude is 10,000 ft, where ISA = +15 ~(2x 10) = +15-20 = -5°C so ISA-10 = 5-10 = -15°C In the computer airspeed window, set pressure altitude 10,000 against OAT -15°C. Against TAS 200 on the outer scale, read off RAS 175 kt on the inner scale. ° Oo e e 0 Ml Figure 2-17 Example 430 Basic NAVIGATION THEORY Airspeed Terminology 1aS: Indicated airspeed. RAS ORCAS: Rectified airspeed or calibrated airspeed. Generally approximately equal to indicated airspeed. ‘tas: True Airspeed. At higher altitudes, TAS is usually greater than IAS/RAS/CAS). Now complete Exercises 2 - Speed. ByChapter 3 31 Direction Dee is obviously of prime importance to accurate navigation, As aircraft navigate with reference to the earth’s surface, we will begin with a brief look at the earth itself. There is a geographical axis passing through two physical points on the surface of the earth about which the planet rotates. These points are the geographic North and South Poles. Any ‘straight’ line drawn around the earth’s surface joining these two points is aligned in a true north-south direction. By convention, the basic reference direction is north, and other directions are measured clockwise from this reference in degrees (°), Since there are 360° in a circle, east is described as 090°, south as 180°, west as 270°, and north as 000° or 360°. Any direction (be it the desired track of an aeroplane, or the direction from which the wind is blowing) can be defined in this way. True Direction If direction is described with reference to true north (the direction to the geographic North Pole), it is called the true direction, symbolised by ‘T’. East is therefore written as 090°T or 090T. The track between town A and town B illustrated below is 327°T. True north pe Tuenorth 3604 000 927°T- West East 270 (090 A 927" South 180 BH Figure 3-1 True direction A more approximate means of describing direction is using the cardinal points, which are the four chief directions of north, south, east and west ~ further divided by the quadrantal points north-east, south-east, south-west and north-west. If necessary, these can be divided even further to give, for instance, NNW (nor-nor-west). Obviously, the 360° method is superior for aeronautical navigation. True direction, however, is a problem for pilots, because most aeroplanes do not have an instrument that can determine the32 BASIC NAVIGATION THEORY direction of true north. The magnetic compass, the prime source of directional information in the cockpit, aligns itself with magnetic north, rather than with true north. NOTE As you will see, this statement does not hold true if there are extraneous magnetic fields, say due to radios or nearby magnetic materials, that are strong enough to affect the magnet within the compass. At this stage, we will assume that the magnet is influenced only by the carth’s magnetic field and none other. Magnetic Direction Near to the true (geographic) North Pole is an area from which the earth’s magnetic field emanates, known as the north magnetic pole to avoid confusion with the geographic pole. Similarly, there is a south magnetic pole located near the true South Pole. A small magnet that is suspended and free to move will seek to align itself with these roughly north-south lines of magnetic force. This is the basis of the magnetic compass. If a compass card is attached to a magnetic ‘needle’, then the magnetic heading of an aeroplane can be read-off against a lubber line, or index, on the compass face. - Magnetic north True north, ‘Axis of. rotation Lines of . magnetic - 333" Figure 3-2 Magnetic direction A direction defined by reference to the north-seeking end of a magnetic compass is known as a magnetic direction. In Figure 3- 2, the direction between the same two towns, A and B, is now described as 333°M. The actual direction between the two towns of course has not changed, only our description of it has, because of the two differ ent reference directions, TN and MN. In the above case, 327°T and 333°M are the same physical direction described differently. Direction Related to Magnetic North Why introduce the complication of degrees related to magnetic north? Because the simple magnetic compass is the most reliable source of directional information. Instruments that display direction relative to true north are both complicated and3 — Direction 33 expensive, and subject to certain operational limitations not associated with the conventional magnetic compass. Even in the most sophisticated aircraft flying today, such as the Boeing 767, Airbus A320 and BAe 146, a simple magnetic compass is installed. In most light aircraft, the magnetic compass is the primary source of directional information, to which other heading or direction indicators (often gyroscopic) are aligned. 6 AMAA MH Figue 3-3 The magnetic compass To obtain accurate directional information from the magnetic compass, you must understand how it operates, and also its inaccuracies while the aeroplane is turning or changing speed. This is covered fully in the Flight Instruments section of Vol. 4 of this series. A summary follows here. A bar magnet that is freely suspended horizontally will swing so that its axis points roughly north-south. The end of the magnet that points towards the earth’s north magnetic pole is called the north-seeking pole of the magnet. N Magnetic pole ‘Small odie | masnet nee a a4 Magnetic pole S“ Figure 3-4 Simple bar magnet The Earth’s Magnetic Field (Terrestrial Magnetism) The earth acts like a very large and weak magnet. Its surface is covered by a weak magnetic field — lines of magnetic force that begin deep within the earth near Hudson Bay in Canada and flow towards a point deep within the earth near South Victoria Land in Antarctica. Because of their proximity to the geographic North and South Poles, the magnetic poles are referred to as the north magnetic pole and the south magnetic pole.34 BASIC NAVIGATION THEORY Variation The latitude-longitude grid shown on charts is based on the geographic poles at either extremity of the earth’s axis of rotation, so the meridians of longitude run true north and true south, and the parallels of latitude run true east and true west. Bi Figue 3-5 The earth has a magnetic field Our small compass magnet, however, does not point exactly at true north and true south. A magnetic compass, if it is working perfectly and is influenced only by the earth’s magnetic field, will point at the north magnetic pole, near Hudson Bay in Canada. At most points on the earth this is a different direction from true north. The angular difference between true north and magnetic north at any particular point on the earth is called the magnetic variation at that point If the magnet points slightly east of true north, the variation is east, If the magnet points to the west of true north, the variation is west. West variation is experienced over the entire UK. Variation at any point on the earth is measured from true north to magnetic north. For example, a magnetic compass in London will point 2° west of true north, i.e. the magnetic variation is 2°W, since magnetic north lies 2° west of true north. In Liverpool the magnetic variation is 3%°W. In the area of the two towns A and. B illustrated in Figure 3-2 it is 6°W; 327°T and 333°M are one and the same direction when the magnetic variation is 6°>W. Variation is the angular difference from true north to magnetic north NOTE Because the earth’s magnetic poles are not stationary, variation changes over time. In the British Isles variation reduces by 7-8 minutes annually (about 1° every 8 years).3 = Direction 35 Isogonals As well as the lines forming the latitude-longitude grids, maps have other lines joining places that have the same magnetic variation. These lines are known as isogonals or isogonic lines. On the UK 1:500,000 aeronautical chart, the isogonals are shown, as dashed lines coloured blue. The 2° west isogonal joins all the places having a variation of 2° west (e.g. Grimsby, Coningsby, Cranfield, Ryde). If you are anywhere on this line, then the message that your compass is giving you about magnetic north can be related to true north; your compass will point at magnetic north, which will be 2° west of true north. Isogonals are lines on a chart joining places of equal magnetic variation. To assist you in choosing the magnetic variation in your area, CAA 1:500,000 UK aeronautical charts show half-degree isogonals. Between these lines you use the appropriate whole number of variation, as shown in Figure 3-6. Z / SW 4.5°W i ~ TEE ie © + ay sR ¥ en x me Sua 4 Between the 2/°W SBY js a = and 814°W isogonals, [BM {Between the 4°W use 3°W variation. ‘and 3}4°W isogonals, > ROSES we use 4°W variation Wa ‘2°W isogonal saat SY 3.5°W_2.5°W A ats 9 I Figure 3-6 Variation is the angle between true and magnetic If magnetic north is to the west of true north (west variation), then °M will exceed °T. Conversely, if magnetic north is to the east of true north (east variation), then °M will be less than °T. An easy way to remember the relationship between true and magnetic is: Variation west, magnetic best. Variation east, magnetic least.36 BASIC NAVIGATION THEORY EXAMPLE 1 While flying on the Continent, you are steering your aeroplane on a heading of 300°M with reference to the magnetic compass. From an aeronautical chart you determine that magnetic variation in the vicinity is 4°W. What is the aeroplane’s heading in true? 4°W isogonal Magnetic ) ) True north )§ north Variation 4°W 1 1 ! 1 | I | ! ht ! | I I 1 I Figure 3-7 Variation west, magnetic best; answer 296°T EXAMPLE 2 Convert 100°T to a magnetic direction in an area where variation is 10°R. 100°T 10°E (Variation east, magnetic least) 090°M (Answer) \ north north 10°E isogonal True } Magnetic \ “| ~ Variation 10°E \ \ \ \ \ \ \ BH figure 3-8 Variation east, magnetic least; answer 090°M The Agonic Line The isogonal that joins places that have zero variation (i.e. magnetic north and true north coincide) is called the agonic line. It passes through Europe. Compass Deviation Unfortunately, the magnet in the magnetic compass is affected not only by the magnetic field of the earth, but by any magnetic field that exists in its vicinity, such as the magnetic fields surrounding3 — Direction 37 the metal structure of the aeroplane, rotating parts in the engine, the radios, etc. The effect of these additional magnetic fields in a particular aeroplane is to deviate or deflect the compass from indicating magnetic north precisely. This imprecision is known as compass deviation. Magnetic \ | Compass north porn ‘Compass deviation Total effect of unwanted magnetic fields of aircraft HDG 090° Bi Figure 3-9 Compass deviation Deviation varies according to the heading that the aeroplane is on, since these unwanted extra magnetic fields are related to the aeroplane itself, If their resultant is diagonal to the longitudinal axis of the aeroplane (Figure 3-10) then, when the aeroplane is steering 045°, or its reciprocal 225°, it will be aligned with the earth’s magnetic field and will not cause the compass needle to deviate. In other words, on these headings, compass deviation is zero. Magnetic = Compass Magnetic = Compass north \ north north \ north Unwanted magnetic fields HDG 045 ee magnetic fields Wl Figure 3-10 Compass deviation nil in this aeroplane on these headings If, on the other hand, the aeroplane is heading east, the alignment of the unwanted magnetic fields will deviate the compass as shown by the deviation card in Figure 3-13. The compass needle will then point towards a compass north that is slightly to the east of magnetic north in this case (by 1°). Even though the magnetic heading might be 090°M, the compass will indicate 089°. ‘An easy way to remember the relationship between magnetic and compass directions is: Deviation east, compass least. Deviation west, compass best.38 BASIC NAVIGATION THEORY EXAMPLE 3 An aeroplane is flying with a heading of 257° indi- cated on the magnetic compass in the cockpit. If, on that heading, deviation is 3°W, what is the aeroplane’s magnetic heading? 257°C. (compass) 3 (Deviation west, compass best) 254°M (Answer) Compass , \ Magnetic Compass \, Magnetic north \ north north \) north Pa Deviation 3°w Deviation 2°W 031°C 029°M 254M HDG 257 HH Fure 3-11 Example 3 Figure 3-12 Example 4 EXAMPLE 4 What compass direction must be steered to achieve a magnetic heading of 029°M, if the compass deviation is 2° west? Deviation west, compass best: 029°M + 2 = 031°C (Answer) The Compass Deviation Card Rather than continually having to carry out deviation corrections to the compass headings, a simpler approach is for each aircraft to have a small placard known as the deviation card displayed near the compass. This card shows the pilot what corrections need to be made to the actual magnetic compass reading (described as °C, for compass) in order to obtain the desired magnetic direction in °M. This correction usually involves no more than a few degrees (and in fact, the correction may be so small that the pilot does not apply it). North DEVIATION CARD FOR 300 30 [60] € [120] STEER oai| ii] West 270: 210] 240] w [300 240 ‘STEER [213] 2a2]273]303]330 ‘ONCE! RADIOS LINO South Figure 3-13 A compass rose and compass deviation card. To achieve a magnetic heading of 270° using this compass, steer 271°C.