Grnd-50 Basic Navigation 2 Direction and Distance

Cardinal Points

N, E, S, W

Quadrantal Points

NE, SE, SW, NW

True Direction

The north geographical pole, known as true north, is the datum point for measurement.

All maps and charts use true north as a datum.

When recorded the letter T follows.

Magnetic Direction

The magnetic poles are in the vicinity of the geographical poles, and the lines of force are roughly parallel to the earth's meridians.

A magnetic compass provides a continuous reference to magnetic north and that is the datum point for measuring magnetic direction.

When magnetic direction is recorded, the letter M follows the numerals (e.g. 090°M).

Variation

angular difference between the direction of true north and magnetic north at a given point

variation east - magnetic least

variation west - magnetic best

Isogonals

Lines which connect geographic points with identical magnetic variations

Compass Direction

the compass is affected by various magnetic influences which radiate from the metallic parts and electrical equipment in the aircraft.

the compass needle does not read magnetic north, but takes up a new direction known as compass north

When compass direction is recorded, the letter C follows the numerals

Deviation

angular difference between the directions of magnetic north and compass north and between all magnetic directions and their corresponding compass directions.

deviation east - compass least

deviation west - compass best

Distance units

Nautical mile, statute mile, kilometer

Nautical Mile

The standard unit of linear measurement used in navigation.

6080 feet

distance can be measured by a comparison with degrees of latitude along a meridian. Each minute of latitude is equivalent to a nautical mile.

Statute Mile

is an arbitrary unit of measurement which is set by law at 5280 feet.

The statute mile has no relationship to angular measurement, and it is seldom used in navigation.

Kilometre

is 1000 meters (3280 feet) in length.

1/10,000th part of the average distance from the equator to the north pole, measured along the meridian which passes through Paris, France.

having a complex relationship to angular measurement, is seldom used in navigation.

Distance conversion

66 NM = 76 SM = 122 km

Measuring Speed

Speed is the rate of change of position, or distance travelled per unit of time. Usually, it is expressed in linear units per hour.

Three expressions of speed

knots (kt), which expresses a rate in nautical miles per hour;

miles per hour (MPH), which expresses a rate in statute miles per hour;

kilometres per hour (km/h).

True Air Speed

The speed at which an aircraft moves through the air, whether the air is moving or stationary

Groundspeed

The speed at which the aircraft moves over the ground beneath it.