Upcoming SlideShare
×

# maps

694 views

Published on

0 Likes
Statistics
Notes
• Full Name
Comment goes here.

Are you sure you want to Yes No
• Be the first to comment

• Be the first to like this

Views
Total views
694
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
14
0
Likes
0
Embeds 0
No embeds

No notes for slide

### maps

1. 1. Recent Changes - Search: Go Recreational Aircraft Association of NZ Freepost 102829 PO Box 15016 Dinsdale 3243 Hamilton Phone 07 825 2800 office@raanz.org.nz Home myRAANZ Pilot info Rules and regs Forms Training Manual Exams Instructors IAs Clubs RecPilot e- zine Marketplace Forums RAANZ (Inc) Contact RAANZ Online Database Miscellaneou s Pages to be updated Upcoming Events Technical Wallpaper edit SideBar View Edit History Print Charts and compass Revision: May 08, 2012, at 05:50 PM Module content 2.1 Latitude and longitude 2.2 Air navigation charts 2.3 Recommended charts 2.4 Map topography 2.5 Magnetic variation and deviation 2.6 Things that are handy to know 2.7 Stuff you don't need to know Ground maps are essential for navigation under the Visual Flight Rules- in fact they are required to be carried on a cross-country. The maps, or charts, used for air navigation are overlaid with a coordinate grid showing the local meridians of longitude and the parallels of latitude. In aviation locations are generally defined in terms of latitude and longitude and chart directions are referenced in relation to true north, but unfortunately the prime navigation instrument – the compass – aligns itself with the magnetic north pole. 2.1 Latitude and longitude Parallels of latitude are imaginary circles drawn around the Earth starting from the equator and reducing in circumference toward the poles. Parallels are identified by the angle which they subtend with the centre of the Earth (measured in degrees, minutes and seconds) and whether they lie north or south of the equator. The equator has a latitude of 0° The North Pole has a latitude of 90°N The South Pole has a latitude of 90°S. New Zealand lies between S34°30' (Kaitaia) and S47°30' (Stewart
2. 2. Island) The equator is a great circle in that it is formed by a plane that passes through the Earth's centre, thus bisecting the Earth's sphere. Meridians of longitude are half great circles, perpendicular to the equator, that extend from pole to pole. The meridians are identified by the angle which they subtend with the centre of the Earth, measured in degrees, minutes and seconds east or west, from the 'prime meridian. The prime or zero meridian – 0° longitude – passes close to Greenwich, England. Subsequent meridians are identified as °East or °West around to 180°. New Zealand lies between E167° (Fiordland) and E178°30' (East Cape) One nautical mile is the length, at the Earth's surface, of one minute of arc of a great circle and the International Nautical Mile is 1852 metres or 6076.1 feet. Consequently one degree of latitude (measured along a meridian) has an equivalent surface distance of 60 nautical miles and one second of latitude is about 31 metres. However seconds of arc are not used in aeronautical publications, latitude and longitude being expressed in degrees plus minutes to two decimal places. For example Te Kowhai airfield north of Hamilton is located at S37°44.42' E175°09.31'. In ultralight navigation accuracies down to one hundredth of a minute (18.5 metres) are generally unnecessary so we round up/down to the nearest minute. 'Lat/long' coordinates should be
3. 3. expressed with the direction from the equator/prime meridian first (S and E), then a group representing the degrees ( S37° and E147°) followed by a group for the minutes ( S37°44' and E175°09'). A knot is a speed of one nautical mile per hour. Back to top 2.2 Air navigation charts A map intended for air or marine navigation is a chart and the chart graticules are latitude and longitude, with the meridians more or less vertical on the sheet. As the Earth is a sphere there has to be a technique to map the image of the surface of the 3-dimensional sphere onto a flat 2- dimensional chart without overly distorting the represented areas. The most suitable method for aeronautical charts is 'Lambert's conformal conic' projection which, although distorting areas a little, allows that the great circle arc, the shortest distance between two points on the surface of a sphere, is accurately represented by a straight line drawn on the chart, and distances anywhere on the chart have the same scale.
4. 4. The meridians on such charts taper towards the poles; on a southern hemisphere chart the meridian spacing at the bottom of the sheet is noticeably less than that at the top. Also you can see that the parallels are slightly curved. If you draw a straight line diagonally across the chart the angle that great circle route subtends with each meridian varies slightly across the chart. All New Zealand aeronautical charts use the New Zealand Map Grid (NZMG) projection. This is a form of conformal conic projection with the following useful characteristics: Centred on New Zealand (Central meridian E173, Latitude origin S41) No distortion of distances between any two points. The central meridian is vertical on the chart, aligned N-S. The shortest distance between any two points is a straight line. For all practical navigation purposes, distances and headings can be taken directly off the chart. The scales used for aeronautical charts are the representative fractions 1:1 000 000, 1:500 000 and 1:250 000. The latter scale means that an actual distance of 250 000 centimetres (2.5 km) is represented by one centimetre on the chart.
5. 5. Directions on air navigation charts are always expressed as the angular distance from the North Pole – true north – in whole degrees from 0° at north clockwise to 360°, i.e. north is both 0° and 360 ° (though usually expressed as the latter), e.g. the direction due east from a particular location is 090°. These directions may be described as bearings, headings, courses or tracks depending on the application. Directions are usually associated with distances expressed in nautical miles thus the bearing and distance of a location 55 nm due east would be expressed as bearing 090°/55. Shape of the Earth For the purposes of aerial navigation the shape of the Earth is defined by a particular model known as the World Geodetic System 1984 [WGS84] which provides the horizontal datum for the chart coordinate systems. Some charts may also show the Geodetic Datum of 1949 [GDA1949] as the datum but this, for all practical navigation purposes, is identical to WGS84. Thus a chart system is built on three basics, which must be defined for use: The projection employed – NZMG projection for New Zealand aeronautical charts. The coordinate system – Latitude and longitude for air navigation. The geodetic datum – WGS84 [or GDA1949] is the standard horizontal datum for New Zealand aeronautical charts. When using a GPS ensure that these three formats have been correctly selected, particularly the WGS84 datum. Chart elevation reference levels New Zealand aeronautical charts use the New Zealand Ellipsoidal Geodetic Datum 2000 (NZGD2000) rather than Mean Sea Level as the reference altitude. As the name suggests, ellipsoidal heights are measured in relation to a reference ellipsoid rather than sea level. For NZGD2000
6. 6. this is the Geodetic Reference System 1980 (GRS80) ellipsoid. Ellipsoidal heights do not relate to the local gravity field of the Earth nor mean sea level (MSL). This means that ellipsoidal heights may be non- zero at sea level and cause water to appear to run uphill. NZGD2000 ellipsoidal heights are approximately equal to MSL near Stewart Island/Rakiura and differ by around 35 metres in Northland. Ellipsoidal heights can be related to the mean sea level datums by using a geoid model (eg, NZGeoid05) The geoid is a notional surface, within the Earth's gravity field, of equal potential gravity which describes the Earth's irregular shape, approximates with msl at the coastline and extends under the continents. The geoid is not the same as the ellipsoid [a smooth, slightly flattened sphere] which mathematically represents the Earth's underlying shape. There are many ellipsoids in use but that of most interest to aviators is the WGS84 ellipsoid used by the global navigation satellite system. The difference in elevation of a particular point on the Earth's surface, when measured against both the ellipsoid and the geoid, can be quite considerable; this is known as the geoid-ellipsoid separation, the extent of which is indicated in the image below.
7. 7. Global navigation satellite systems (eg, GPS) produce ellipsoidal heights. This is because mathematical calculations on the ellipsoid are simpler to carry out than on the undulating mean sea surface. Some GPS receivers will output heights in relation to sea level, however to derive these they will have applied a geoid model to transform the ellipsoidal heights. The International Civil Aviation Organisation specifies that the local value [known as the 'N value'] of the geoid-ellipsoid separation should be shown on aeronautical navigation charts but the values are not shown on new Zealand charts. The local N value is of little significance to recreational aviators (although it should be noted that a GPS instrument may give an apparently incorrect height if the software doesn't adjust for the local 'N' value) but may be of great significance to IFR pilots and designers of GPS approaches when GPS achieves sole-means navigation status. In practical microlighting visual navigation applications, the difference between NZGD2000 reference and Mean Sea Level is not significant. In Northland you may be 35m closer to the ground than you thought you were- just look out the window when you are landing!. Back to top
8. 8. 2.3 Recommended charts The charts recommended for ultralight and light aircraft flight planning, in- flight navigation and sourcing VHF radiocommunications data, are: Visual Planning Charts (VPC). These are two 1:1,000,000 charts on a single double sided sheet covering New Zealand- North and South islands. They are intended for pre-flight planning of routes, distances and time estimates. They do not have detailed low-level and terminal airspace information, and should not be used for in-flight navigation. Visual Navigation Charts (VNC). These are a series of charts of varying scales- 1:500,000 (B series), 1:250,000 (C series) and 1:125,000 (D Series). They contain detailed and complete information on airspace below 9500 feet, and are intended for pre-flight planning and in-flight navigation. The charts are updated on any significant change in airspace or navigation information. It is a good idea to have all the charts covering your intended area of operations- the smaller scale charts (1:500,000) are suitable for less complex airspace areas, but the large scale charts (1:250,000 or 1:125,000) allow you to 'zoom' in on critical areas with great detail and clarity- very useful around CTRs. Christchurch Airport at different map scales
9. 9. Information contained in the VNCs includes: Airspace- boundaries, upper and lower levels, ATS station and frequency, transponder requirements Maximum elevation figures (MEF) for each 15 minute quadrangle. Detailed contours, elevations and spot heights. Main roads, rivers, rail and transmission lines. Certified airfields, frequencies, elevation, length and vector. Special airspace- GFAs, SPAs, MBZs, transit lanes, restricted areas, danger areas, MOAs- and conditions of entry. Reporting points The VNCs are essential flight planning and navigation tools- you are well advised to keep a personal set covering the areas you fly. And it is important that you update on each revision- bad information can be more dangerous than no information. VPCs and VNCs are available from most aero clubs, some microlight clubs, or direct from Airways at the AIP shop. Carriage of flight documentation From Civil Aviation Regulations CAR Part 91: 91.221 Flying equipment and operating information (a) A pilot-in-command of an aircraft must ensure that the following equipment and information, in current and appropriate form, is accessible to every flight crew member of the aircraft: o (1) an accurate means of indicating the time: o (2) appropriate aeronautical charts: