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basic air navigation
Navigation is the art and science of
getting from point "A" to point "B" in the least possible time without
losing your way. In the early days of aviation, navigation was mostly
an art. The simplest instruments of flight had not been invented, so
pilots flew "by the seat of their pants". Today, navigation is a
science with sophisticated equipment being standard on most aircraft.
The type of navigation
used by pilots depends on many factors. The navigation method used
depends on where the pilot is going, how long the flight will take,
when the flight is to take off, the type of aircraft being flown, the
on-board navigation equipment, the ratings and currency of the pilot
and especially the expected weather.
To navigate a pilot needs to know the following:
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Starting point (point
of departure)
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Ending point (final
destination)
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Direction of travel
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Distance to travel
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Aircraft speed
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Aircraft fuel capacity
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Aircraft weight &
balance information
With this information
flight planning can commence and the proper method of navigation can be
put to use.
Basic Navigation
Pilotage
For a non-instrument rated, private pilot planning to fly VFR (Visual
Flight Rules) in a small, single engine airplane around the local area
on a clear day, the navigation is simple. The navigation process for
such a local trip would be pilotage. (Bear in mind, however that the
flight planning and preflight for such a trip should be as thorough as
if the pilot is preparing to fly cross-country.)
The pilotage method of navigation developed naturally through time as
aircraft evolved with the ability to travel increasingly longer
distances. Flying at low altitudes, pilots used rivers, railroad tracks
and other visual references to guide them from place to place. This
method called pilotage is still in use today. Pilotage is mainly used
by pilots of small, low speed aircraft who compare symbols on
aeronautical charts with surface features on the ground in order to
navigate. This method has some obvious disadvantages. Poor visibility
caused by inclement weather can prevent a pilot from seeing the needed
landmarks and cause the pilot to become disoriented and navigate off
course. A lack of landmarks when flying over the more remote areas can
also cause a pilot to get lost.
Using pilotage for
navigation can be as easy as following an interstate highway. It would
be difficult to get lost flying VFR from Oklahoma City to Albuquerque
on a clear day because all a pilot need do is follow Interstate 40
west. Flying from Washington, DC to Florida years ago was accomplished
by flying the "great iron compass" also called the railroad tracks.
Dead Reckoning
"Dead" Reckoning (or "Ded" for Deductive Reckoning) is another basic
navigational method used by low speed, small airplane pilots. It is
based on mathematical calculations to plot a course using the elements
of a course line, airspeed, course, heading and elapsed time. During
this process pilots make use of a flight computer. Manual or electronic
flight computers are used to calculate time-speed-distance
measurements, fuel consumption, density altitude and many other en
route data necessary for navigation.
The estimated time en route (ETE) can be calculated using the flight
distance, the airspeed and direction to be flown. If the route is flown
at the airspeed planned, when the planned flight time is up, the
destination should be visible from the cockpit. Navigating using known
measured and recorded times, distances, directions and speeds makes it
possible for positions or "fixes" to be calculated or solved
graphically. A "fix" is a position in the sky reached by an aircraft
following a specific route. Pilots flying the exact same route
regularly can compute the flight time needed to fly from one fix to the
next. If the pilot reaches that fix at the calculated time, then the
pilot knows the aircraft is on course. The positions or "fixes" are
based on the latest known or calculated positions. Direction is
measured by a compass or gyro-compass. Time is measured on-board by the
best means possible. And speed is either calculated or measured using
on-board equipment.
Navigating now by dead reckoning would be used only as a last resort,
or to check whether another means of navigation is functioning
properly. There are navigation problems associated with dead reckoning.
For example, errors build upon errors. So if wind velocity and
direction are unknown or incorrectly known, then the aircraft will
slowly be blown off course. This means that the next fix is only as
good as the last fix.
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