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Navigation Terminology Part 1

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rc2017's version from 2017-08-05 12:08

Section

Question Answer
CourseCourse is the INTENDED flightpath over ground with a specific cardinal direction
TrackTrack is the ACTUAL path covered over ground with wind effect taken into account
Track Made GoodThe actual path of the aircraft over the surface of a track as distinct from the intended track to be flown. It is often indicated by a double arrow on charts and maps.
Drift AngleThe difference angle between Course and Track is called Drift angle. Starboard dift and port drift for example
HeadingHeading is the compass direction the aircraft's nose is actually pointing towards, along it's longitudinal axis. It's measured clockwise from north. If measured from True North - Then True Heading. If Magnetic North - Then Magnetic Heading
Compass HeadingThe direction the aircraft compass needle is pointing toward
True North True North is the direction along the earth's surface towards the geographic North Pole. So it's north directly over the earth's axis
Magnetic NorthSince the earth's axis is slightly tilted.. the north direction a compass needle points corresponds to Earth's magnetic field lines. This is Magnetic North. Currently MN is somewhere in North Canada polar region.
VariationVariation is the angle on the horizontal plane between magnetic north and True North. It is measured from the TN to the MN. If the Magnetic North is west of the True North, variation is west, and vice versa Example:
If MN is 4º west of TN, variation is 4º W or -4º
If MN is 8º east of TN, variation is 8º E or +8º
DeviationDeviation is the angle difference between magnetic north and compass north. Any magnetic or ferrous material or electrical equipment on or near the aircraft compass will affect the local magnetic field and may deflect the compass needle away from the Magnetic North (MN). This means that
the Compass may not show the Magnetic Heading accurately.

Deviation is measured from the Magnetic North to the Compass North. If the Compass North is west of the Magnetic North, deviation is west, and vice versa.
Example:
If CN is 3º west of MN, deviation is 3º W or -3º
If CN is 5º east of MN, deviation is 5º E or +5º.
Wind Correction Angle (WCA)WCA or Crab angle is the amount of correction an aircraft must be turned into the wind in order to maintain/track a course
True HeadingTrue Course -/+ WCA
Magnetic HeadingTrue Heading -/+ Variation
Compass Heading (How to calculate)Magnetic Heading -/+ Deviation
BearingA bearing is the direction from your location (Aircraft) to/from any distant point (Station) given in degrees clockwise. - Either heading to/from the Station. This is called 'Relative Bearing'. The position of an object relative to the longitudinal axis of the aircraft. RB is used mostly on ADF equipment to obtain the station’s relative position.

Or with respect to the magnetic north called 'Magnetic Bearing' or True North called 'True Bearing'.

Basically BEARING is the angular difference between where I *am* going and where/which station I *want* to be going (relative bearing)
or where I am going with respect to the magnetic north (magnetic bearing).
Great CircleA circle on the surface of the earth whose plane passes through the centre of the earth (equatorial plane)
It is also the shortest distance between any two points on the earth. Example: San Francisco to Abu Dhabi would fly great circle over north polar region as faster route compared to SFO> NYC> LON> Abu Dhabi
Rhumb LineA curved line on the surface of the earth that cuts all of the meridians at the same angle. Arc crossing all meridians of longitude at the same angle. It is a path with constant bearing as measured relative to true or magnetic north. Example: London to Barbados would fly a rhumb line track
Isogonal LinesIsogonal lines are lines of constant wind direction. Lines on a map connecting places of equal variation. Labeled East or West according to position relative to True North
Agonic LinesA line connecting places of zero variation. Two agonic lines; one in North America and one on the opposite side of the Earth
One in 60 ruleThis is a rule that can be used to help determine either how far you are off course or how much of a correction needs to be made to regain your course.
The rule states that: An error in the track of one degree will cause an error in position of about one mile in a distance of 60 miles
Wind TriangleThe wind triangle is a vectors representation of the desired course, wind, correction angle and velocities.
Navigational calculation allowing determination of true heading with a correction for crosswinds on course
In air navigation, the wind triangle is a graphical representation of the relationship between aircraft motion and wind. It is used extensively in dead reckoning navigation.

True Course (TC) is the desired ground track measured clockwise from the Geographic True North. The TC is noted by a single arrow.
True Heading (TH) is the heading to be flown to maintain the desired track measured clockwise from the Geographic True North. The TH is noted by a double arrow.
Wind Direction (W) is the direction from which the wind is coming measured clockwise from the Geographic True North. The Wind Direction is noted by a triple arrow.

The Ground Speed (GS) is proportional to the True Course, the True Airspeed (TAS) is proportional to the True Heading (TH) and the Wind Velocity (V) is proportional to the Wind Direction (W)
Dead ReckoningIn navigation, dead reckoning(or deduced reckoning) is the process of calculating one's current position by using a previously determined position, or fixed checkpoint, and advancing from that position using speed, elapsed time and course.

A pilot can plot the 9am position fix (departure station), and then using the current course and speed, estimates the position at 9:30am and 10am. Dead Reckoning uses the basic formal Distance = Speed x Time.

The wind triangle is used to calculate the effects of wind on heading and airspeed to obtain a magnetic heading to steer and the speed over the ground (groundspeed).
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