Knots and Nautical Miles
Knots and Nautical Miles All navigation uses the Nautical Mile as
the unit of distance. Traditionally a nautical mile is 6,080 feet but
more precisely 6,076.11549 feet. In metric measurement it is 1,852
meters, which is one minute of arc of a great circle of the Earth.
Even under the metric system, the unit of distance for navigation is
still called the nautical mile. One knot converted to miles per hour
(mph) would be approximately 1.15 mph. One mile per hour would be 0.868
knots. A statute mile is the common "mile" with a length
of 5,280 feet. Therefore a statute mile is not as long as a nautical
mile. One nautical mile would equal approximately 1.15 statute miles.
Making the conversion from nautical miles to statute miles would be
done as 120 nautical miles x 1.15 statute miles = 138 statute miles.
Converting from statute to nautical miles would require dividing by
1.15. Therefore 200 statute miles would equal (200 / 1.15 = 174) 174
Many of the air navigational terms come from our heritage of sea
navigation. In the days of wooden sailing vessels, the speed of a
sailing ship was measured by unraveling a knotted rope into the water
behind the moving ship. The number of knots in the rope that passed
over the railing in a given amount of time would indicate how fast
the ship was moving (its number of knots). It is this same term that
is used in aeronautics and aviation to indicate flight speed, however
without the knotted rope trailing behind the aircraft.
Latitude / Longitude
A reference system is used with which an exact location on the Earth's surface
can be pinpointed. This system uses designated lines of latitude and longitude.
Latitude measures north and south of the equator, and longitude measures
east and west of the prime meridian (located in Greenwich, England).The latitude
of an exact location is expressed in terms of degrees, minutes and tenths
of a minute. One minute of latitude equals 1/60th of a degree. The North
Pole, for example, is 90 degrees north of the equator. This is written as
N9000.0. The South Pole is located at 90 degrees south of the equator and
is written as S9000.0. The longitude of an exact location is expressed in
terms of degrees, minutes and tenths of a minute, also. One minute of longitude
equals 1/60th of a degree. The longitude of the airport at Miami, Florida
is located, for example, approximately 80 degrees west of the prime meridian.
Precisely, this is written as W08016.6, and expressed as 80 degrees and 16.6
minutes west of the zero meridian. The airport at Perth, Australia is located
approximately 115 degrees east of the zero meridian and is written as E11557.5.
This is expressed as 115 degrees and 57.5 minutes east. Combining both latitude
and longitude, the location of the airport in Miami, Florida is N2547.1 and
W08016.6. This measure is used globally and communicates clearly to all pilots
the same locations.
In navigation and surveying all measurement of direction is performed by using
the numbers of a compass. A compass is a 360° circle where 0/360° is North,
90° is East, 180° is South, and 270° is West. Runways are laid out according
to the numbers of a compass. A runway's compass direction is indicated by
a large number painted at the end of each runway. A runway's number is not
written in degrees, but is given a shorthand format. For example, a runway
with a marking of "14" is actually close to (if not a direct heading
of) 140 degrees. This is a southeast compass heading. A runway with a marking
of "31" has a compass heading of 310 degrees, that is, a northwest
direction. For simplicity, the FAA rounds off the precise heading to the
nearest tens. For example, runway 7 might have a precise heading of 68 degrees,
but is rounded off to 70 degrees.
Move Cursor over Runway Designator and Observe Compass Heading
Each runway has a different number on each end. Look at the diagram
at left. One end of the runway is facing due west while the other end
of the runway is facing due east. The compass direction for due west
is 270 degrees ("27"). The compass direction for due east
is 90 degrees ("9"). All runways follow this directional
layout. This runway would be referred to as "Runway 9-27" because
of its east-west orientation.
Applying this to navigation means that pilots do not turn right
or left, or fly east or south exactly. To fly east the pilot would
take a heading of 90° . To fly south, the compass heading would be
180°. Look at the compass at left to note the compass headings for
northeast, southwest and west.