Map Reading Technique

Wg Cdr Rajagopal

Navigation using Maps and Charts

Index

Topographical Maps

  • Topographical Maps show natural and man-made features and are used for basic navigation
  • Used for visual map reading during visual navigation
  • Maps normally do not show radio navigation facilities since they are used for map reading during Visual Navigation
  • Coverage of a maps are generally lesser than that of charts

Aeronautical Charts

  • Charts are used for Instrument or Radio Navigation
  • Aeronautical Charts show Radio Navigation facilities and Air Routes since they are used for Instrument Navigation
  • Coverage of a charts are normally much larger than maps

Depiction of Terrain Elevation in Maps and Charts

  • The height above mean sea level of natural features is called elevation
  • Elevation of terrain can be depicted as Contour Lines, Layer tinting and Spot heights

Contour Lines or Contours

  • Contours are lines joining places of equal elevation in feet or meters
  • Steep slope is indicated by contours close to each other while spread out contours indicate a gentle slope

Layer Tinting

  • Layer tinting is the method of colour filling contour lines with shades of brown and green
  • Colour codes and corresponding elevations are provided in the margins of maps

Spot Heights

  • Elevation of prominent peaks are shown as spot heights
  • Spot heights are indicated inside a white or yellow rectangle for easy identification

Maximum Elevation Figure (MEF)

  • Maximum Elevation Figure (MEF) indicates the highest obstacle in maps or charts
  • MEF is provided for half or full degree rectangle of latitude and longitude
  • Topographical maps generally provide MEF figure
  • Safety margin is not added to MEF printed on maps and hence the required safety margin has to be added during flight planning

Calculation of Maximum Elevation Figure

  • Maximum En-route Figure is calculated in three steps
  • Step 1 – Take highest natural feature and add 300 feet and add 300 feet to cater for features on top of peaks
  • Step 2 – Take the highest man-made feature where elevations are accurately surveyed
  • Step 3 – Select the higher of Steps 1 and 2 and round off to next hundred feet for reporting

Minimum Safety Altitude (MSA)

  • Minimum Safe Altitude (MSA) is obtained by adding safety margin to Maximum En-Route Figure
  • Minimum safety altitude is depiction of safe obstacle clearance altitude in Air navigation charts
  • Safety Margin depends on the calculated Maximum En-route Figure (MEF)
  • For Maximum En-route Figure of less than 5000 feet add a safety margin is 1000 feet
  • Safety margin is 2000 feet for Maximum En-route Figures greater than 5000 feet

Map Colour Codes

  • Standardised colour codes are used to depict features on all Topographical Maps
  • Blue indicates water features like rivers or lakes
  • Green indicates woods or forests
  • Roads are shown as red lines
  • Black lines are used for railways
  • Cities or built-up areas are indicated in yellow colour

Map Reading Technique

  • Map to ground technique is used if aircraft is close to Planned Track
  • Map to Ground means to read features on the map and look out for them on ground
  • When unsure of position, Ground to Map technique is used
  • Look at prominent features on ground and try to locate them on the map

Visual Check Points

  • It is important to select the correct visual check points depending on terrain and season
  • Clearly visible, visual check points must selected during planning stage
  • Large, Unique and check points with a contrast colour would be easily visible from air
  • Tall towers are easily visible, but to be avoided for safety reasons
  • Natural features like Coastlines, Lakes or hills make good check points
  • Man-made features like towns, road or rail crossings can be used but must not be flown over at low altitudes
  • Airfields and maritime beacons can also be good check points during day and night

Visual Navigation Hazards

  • Weather conditions and terrain can cause difficulties in visual navigation
  • Check points may be scarce in deserts, jungles or under snow cover
  • Distance and height assessment are difficult in certain terrains
  • Blowing snow causes earth and sky to blend causing white out
  • Snow, water and desert conditions makes navigation difficult
  • Night flight over seas may cause disorientation

Visual Navigation Techniques

  • Important Visual Navigation Techniques
  • 1. Check and synchronise compass at setting heading from a starting point
  • 2. Synchronise compass during alteration of headings at turning points
  • 3. Check altimeter setting and confirm flight is at safe altitude
  • 4. Start or restart stopwatch to keep track of running time
  • 5. When unsure of position resolve them using navigational aids
  • 6. Check fuel and aircraft systems and follow local lost procedure

Actions when Unsure of Position

  • 1. When unsure of position commence Local lost procedure
  • 2. Check Compass and Air Speed Indicator for heading and speeds
  • 3. Climb higher to increase visual as well as radio horizon
  • 4. Use navigational aids like VOR, DME, VDF, radar to fix position
  • 5. Calculate a Deduced Reckoning position using the last known accurate fix
  • 6. Use track and ground speed and flying time to calculate DR position
  • 7. Draw a circle of uncertainty around the DR position and start map reading
  • 8. Use ground to map technique for map reading
  • 9. Turn towards a good visual line feature and follow it till a known position

General Map Symbols

  • Symbols used in Maps may be natural and man-made features
  • Topographic symbols like contour lines or spot heights
  • Hydrographic symbols like canals and lakes
  • Built up areas like towns, highways and aerodromes
  • Aeronautical Symbols of Radio navigation aids like Non-directional beacons
  • Air traffic symbols like restricted areas or flight information regions
  • Obstacles like transmission cables or high-rise buildings

Best of luck