Navigation: Dead Reckoning, Charts and Radio Aids
The Earth and charts
Know the shape of the Earth (oblate spheroid), the meaning of latitude and longitude, and the properties of map projections. A Mercator chart is conformal - angles are correct and a straight line is a rhumb line - but scale varies with latitude. A Lambert conformal conic is used for many aeronautical charts and has a great circle that is nearly straight.
Dead reckoning
Be able to compute track, heading, groundspeed and wind correction. The triangle of velocities links true airspeed, wind velocity and groundspeed. Remember the difference between true, magnetic and compass headings: variation applies between true and magnetic, deviation between magnetic and compass.
Radio navigation
Understand VOR (radial from the station, line of position), DME (slant range, so indicated distance exceeds true distance at high altitude), NDB/ADF (relative bearing, and the trap of ADF errors such as quadrantal error), ILS (localiser and glideslope, and the meaning of the decision altitude), and GNSS (RAIM, integrity and the difference between accuracy and integrity).
Traps
- Mixing up radial and bearing: a VOR radial is the line from the station outward; your bearing to the station is the reciprocal.
- Forgetting DME slant range error is greatest overhead the station.
- Applying variation in the wrong direction - east is least, so true to magnetic add easterly variation.
Worked example
True course 090, easterly variation 5°: magnetic course is 090 − 5 = 085. If deviation is 3° east, compass course is 085 − 3 = 082. Mnemonic: east is least, west is best, applied from true to compass.