Home Table of Contents

2.1 Terminology


Back Next

Express direction as a three figure group and in the clock code
Define True (T), Magnetic (M), and Compass (C) North

Heading (HDG) is the direction the nose of the aircraft points relative to magnetic north pole and expressed as a three figure bearing, 000 through to 360 degrees.

The numbers on a runway, is the direction of the runway which match the directions on a compass. Each runway has a 2 digit number representing the first two numbers of the degree the runway faces. Think of a circle and compare it to a compass. East would be 090 degrees, South 180 degrees, West 270 degrees, and north 360 degrees.

In the example runway 33 is facing North North West or 330 degrees. Runway 27 is facing West or 270 degrees. Runway 09/27 is the same strip of pavement but depending on which direction you are flying determines which runway it is.

Runways are identified by a two-digit number that corresponds to its magnetic heading. The direction that your runways are pointing within that circle, dictates which two-digit number it will be assigned. Another interesting fact is: whatever number is determined to the top of the runway, the bottom of the runway will *always* be 180 degrees less. For example, if your runway at the north or top points to 330 degrees, the bottom of the runway would then be... 330 - 180 = 150. Now that you know which way your runway runs, you have to convert the direction into a two-digit number. Drop the zeros in both sums. 330 becomes... 33 and 150 becomes... 15. When there is a letter identifier associated with a runway, there is either 2 or 3 parallel runways that could be used. These are indicated by (L) - left, (C) - center, or (R) - right. Which runway you will be taking off from or landing on depends on the time of day and winds/weather, or if the runway is even operational. You should check with the airfield you'll be operating into/out of for more information.

Distance, Speed and Velocity

State the units used for distance:
navigation - nautical miles(nm)
visibility - metres (m), kilometres (km)
Knot (kt)

The term knot is rate of speed. The knot has a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph and is used in meteorology, and in maritime and air navigation. For example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour.

Wind Velocity (W/V)

A South-Easterly wind direction would be coming From approximately 130 degrees, relative from the true north pole.

A North-North-West wind direction would be coming From approximately 340 degrees, relative from the true north pole.

The speed and direction of the wind is called wind velocity. It is expressed in five or six digits-the first three indicating the true direction from which the wind is blowing and the last two or three digits indicating the speed in knots. Thus, if the wind is blowing at 20 knots from the east, it will be expressed as 080/20. If the wind speed is, however, 110 knots, it will be expressed as 090/110.

Velocity is a branch of classical mechanics which describes the motion of bodies. Velocity is a vector physical quantity of both magnitude and direction and are required to define it. Velocity is the rate of change of the position of an object, equivalent to a specification of its speed and direction of motion, e.g. 30kt (nm/h) from the north. If there is a change in speed, direction, or both, then the object has a changing velocity.


Time is express as a 4, 6 and 8 figure 24 hour group and is mentally convert from local time (EST -10, CST -9.5, WST -8), to UTC and vice versa.

Vertical Measurement

The unit feet (ft) is used for vertical measurement:

The term "Height" is a vertical measurement in feet between to objects. For example, the aircraft is 1000ft above ground level (AGL).

The term "Altitude" is a vertical measurement in feet above mean sea level to an object in the air. For example, the aircraft is 1000ft above mean sea level (AMSL).

The term "Elevation" is a vertical measurement in feet above mean sea level for a land mass. For example, the airport is 1000ft above mean sea level (AMSL).

The units used in aviation are:
Temperature is in degrees Celsius (C)
Pressure is in Hectopascals (hPa)
Weight can be in Kilograms (kg) or Pounds (lb)
Volume is in Litres (l) or US Gallons (USG)
Runway direction is given as a two figure group relative to magnetic north and dimensions are expressed in meters and degrees.