AERIAL NAVIGATION
“The Art of Getting There”
Or Not!
A Short History
by: Don R. Jordan
R.C. (Bob) Sherman
It is my belief that there were three main
factors that contributed to the high aviation accident rate,
particularly between the years 1940 and 1946. They were: The rush
of war training, the young age of the trainees, and the far too rapid
advancement, or lack thereof, in aviation technology. Much of
what we now know about flying in general (e.g., weather, structural
design, and navigation, etc.) was discovered or first put into practice
during those turbulent years of World War II. Aerial navigation
in particular was in its infancy during this time. The early inadequate
navigation systems were at their worst when the weather was bad and
they were needed most. Add many trainees into the mix and you will find
the combination accounted for many of the accidents laid out in this
book.
There are also a few sad tales of fatal, or near
fatal, accidents in this book that were caused by equipment failure as
well. Engine fires or engine failures were somewhat common in
earlier aircraft engines. With those big old gas-guzzling radials of
that bygone era, which were prone to leaking fuel and oil, or coming
apart for no apparent reason, installed on virtually every U.S. bomber,
and nearly all of the fighter aircraft of World War II, there was bound
to be more than just a few failures.
Navigational issues that cause accidents have pretty
much been eliminated. Modern technology has made aerial
navigation, when done properly, extremely safe and accurate. Now
and then you will still read about an accident that was caused by
equipment failure. However, I don’t consider engine stoppage from
fuel exhaustion as equipment failure! Unless of course you
consider that mass of gray matter between your ears as equipment!
And just for the record there is a difference between “fuel starvation
and fuel exhaustion”. Even though in general they are both caused
by failing to use that same gray matter mentioned above, the outcome is
generally the same. The story entitled “The Fairfield Suisun
B-24” is an example of fuel starvation.
There are many methods of navigation available to
the world traveler, whether on land, sea, or in the air. The
invention and perfection of the radio transmitter spawned a variety of
new very accurate and reliable forms of navigation. Over time some have
become obsolete, and some have faded into history. Others have been
refined to such a point as to allow a traveler to pinpoint his location
to within a few feet anywhere on the earth’s surface. My purpose
here is not to teach the reader the finer details of how these systems
operated, or how to use them. Instead, I just want to give you some
idea of the different methods of navigation available, and to give you
a little idea of how they worked so that you will better understand why
or how an aircraft ended up as it did in the following stories.
I’m sure the experienced pilot will find this chapter boring, or over
simplified. But the non-pilot, or Student Pilot readers may find
some helpful information here. Hopefully when they finish reading
this chapter they will have a better understanding of what is meant
when I later refer to a “Beam”, or a Waypoint, and a DF bearing.
In the early days of aviation there were some pretty
horrendous accidents caused primarily by navigational inadequacies or
errors. But navigational methods and techniques have changed
dramatically over the centuries. I know what you’re going to say,
“But man hasn’t been flying for centuries!” That’s true, but he
has been navigating on land, and the high seas for more than just a few
centuries. The earliest land navigators used a form of ‘Pilotage”
to get around. Pilotage is basically getting to where you want to
go by reference to familiar, or known landmarks. You use Pilotage
every time you use your car to go across town to work.
For example, every morning you go down to the end of
the street (a check point of sorts). Then turn right and go another two
blocks (another check point). Go left and travel for five miles to the
big parking lot on the left (a check point). Pull in and go to
your workstation or desk. Unless you miss one of those check
points, you will successfully navigate to work everyday by reference to
familiar and known landmarks. That is “Pilotage”!
A pilot in the air can also use Pilotage to make a
very safe and successful cross-country flight. When I departed my
home airport at Merced, California, and headed for Fresno to visit my
mother, I would generally fly down highway 99 to the small town of
Chowchilla (a check point) where I would then contact Fresno Approach
Control. Then I’d continue on until I crossed the San Joaquin
River (a check point). At that point I’d turn southeast over the
city and fly until I could see the Air Terminal come into view.
After few more precise turns, over a few more prominent landmarks, and
I was on the ground at FYI (Fresno Yosemite International). I had
successfully used Pilotage as my primary method of navigation.
The primary factor that makes Pilotage useless, is weather. If
you can’t see the landmarks, you can’t get there from here, because you
don’t know where “here” is, and where “there” should be!
Ok! So how did Christopher Columbus, Ponce de
Leon, Sir Francis Drake and other famous early seafarers find their way
on the high seas where there were no landmarks? Well they
actually did use landmarks, except they weren’t on the land (sea). They
were in the sky! They used the sun, the moon, certain planets,
and the stars to determine position. It was a complicated
process, which involved the use of a couple of special “tools” to work
properly. This form of navigation was called Celestial
Navigation. It worked well, but it did have its
limitations. Just ask Amelia Earhart, if you can find her!
With all the new advances in technology almost nobody uses Celestial
Navigation in its original form anymore. I guess I had better
qualify that statement by saying that nobody uses Celestial navigation
in private or commercial aviation anymore. However, it the
primary form of navigation used by the astronauts, and by other long
range space vehicles.
Celestial navigation is extremely difficult for use
in a single pilot aircraft. For one thing it required the use of
a special tool called a sextant. There were much earlier forms of this
instrument that used different names, but I’m mainly dealing here with
Celestial navigation for use in aviation. This instrument measured the
height of a heavenly body above the horizon at the viewer’s
location. Can you imagine getting the precise angle in a bouncing
airplane, or a rolling ship? The next special tool needed was a
Chronometer. A Chronometer is basically a very accurate timepiece
that had been previously calibrated to a time standard at the Royal
Observatory in Greenwich, England. I won’t go into why they use
Greenwich, England as the standard for time around the world, but
Greenwich Mean Time, also called Zulu, GMT, and more recently, UT for
Universal Time. A universal time allows navigators, travelers, the
military, and all affected anywhere in the world, to relate to a common
time standard regardless of local zones. However, local zones
still remain more convenient for those who spend all their time in the
local areas. Everybody reads from the same clock, set to the same
standard, which is UT. Enough said about “time”!
After the Celestial navigator measures the angle of
the sun or star he’s viewing, he reads that angle above the horizon of
that body in degrees and minutes as recorded on the sextant. He
then makes a note of the exact time that he took that reading. He
will then take two more ‘shots’ on other heavenly bodies at a different
azimuth (horizontal direction), “mark” the degree reading and time, and
then retire to his navigational table to plot his location. Three
‘shots’ or bearings are needed for a reliable FIX.
Prior to determining the Az and approx. Hc as above,
[Azimuth & Height] for selected celestial shots, one needs to
consult an [Air or Nautical] Almanac to determine the relationship of
the Celestial sphere to the Terrestrial sphere to synchronize the
timing. One second can make a difference of a mile or two, thus
the need for the exact time. ‘Plotting a position’ is the physical act
of drawing the lines on the chart. Where they cross is called the
FIX. However, since the aircraft or ship is moving right along on
its course, and this whole process may take up to fifteen minutes to
compute, one is well beyond the ‘FIX when all is said and
done.
It takes a lot of work, and a lot of mathematical
calculations. As I said earlier, using Celestial navigation was
very difficult for use in the single pilot airplane. One must
have a dedicated navigator to be able to get and plot accurate
readings. At least now you have a general idea of what Celestial
navigation is, and how it was used.
One of the first forms of early navigation, still
used to some degree today is called “Dead Reckoning”. It involves
the plotting of vectors to predict one’s position, based on the
diagrammatic addition of vectors; [lines equivalent to ones speed,
orientated to the direction traveled], based on distance,
estimated ground speed, time, and heading, to indicate one’s planned
position at any moment in time. You don’t have to see the ground
at all to navigate using Dead Reckoning. But the navigator must find
his actual position from time to time to verify their DR.
Since DR is really an estimate, or an educated guess really, only a
very foolish or daring pilot who would begin to let down from altitude
in mountainous terrain, and in bad weather based on DR navigation
alone. The mountain peaks and hillsides are littered with such
daring pilots! The “Gambler Special”, and the “Western Airlines Flight
23” were both relying on Dead Reckoning navigation when they both hit
an unseen mountain peak in the middle of the night.
The basic problem with DR navigation is that it
requires a flat surface for laying out a map, good light, and several
minutes of uninterrupted concentration to draw the vectors; not a
workable system for a solo pilot. It’s inaccuracies stem from not
holding the heading or speed and not knowing the wind or current.
It was a useful system if there was a dedicated navigator
onboard. The Navy did equip solo pilots with a small lap plotting
board. It was better than nothing. However, both Charles
Lindbergh and Amelia Earhart successfully used DR navigation to find
Ireland, but Amelia made her landfall well north of where she intended.
All ships, and aircraft over the ocean, used DR
between Celestial fixes. Especially a war ship taking evasive
action during a heated battle, added a new vector every time it
turned! After World War I many Army pilots used surplus JN-4
“Jennys” to fly the mail across the United States. Early on the
only forms of navigation were Pilotage and DR. Many pilots got
lost, and many accidents occurred as a result. So in the mid
1920s lighted beacons began to appear all along the mail routes.
This was a dramatic improvement, and worked well as long as the weather
continued to cooperate. In marginal weather, or during nighttime
hours, pilots could just follow the lights to the next landing field.
However, during daylight hours the beacons were generally useless, but
the red course blinkers that gave a code number identified that
particular beacon, provided the pilot with a Fix. Lighted
beacons are still in use today at every civil and military airport in
the world. At night they identify the location of the airports,
and will let the pilot know whether it is a civil or military airport.
It was about this time that somebody got the idea of
putting the names of cities on rooftops, often with an arrow pointing
the direction of the airport. A pilot could fly over a city, and
look down to read the name of the city painted in four-foot high
letters on the top of the most prominent building in the area. In
the San Joaquin Valley of California, just south of the small town of
Merced there is a large, very old barn on the west side of the
freeway. Painted on the roof in four foot high letters are the
words “Merced Tobacco”. This was not only an advertisement for
Merced Tobacco, but also a checkpoint for incoming pilots.
In about 1929 the modern marvel of radio navigation
was introduced. The LF (Low Frequency) radio ranges began to
spread across the country. I won’t go into all the technical
details of how it worked, but I will tell you just enough so that you
will understand how the pilot used the system to navigate with. I
have included several stories in this book where the accident aircraft
was using the LF Radio Range system as its primary method of navigation.
Basically, it used a ground based Low Frequency
transmitter producing a coded “A”, and an “N” from two separate
antennas on the same site. These transmitters were generally spread out
about two hundred miles apart. They would be closer in
mountainous terrain, or where obstacles tended to interfere with the
signals. These transmitters sent out their signals aimed at each
other. This signal, or Beam”, was approximately three degrees in
width, and formed an electronic “Airway” in the sky. Any aircraft
equipped with a Low Frequency radio receiver could navigate along the
Airway to get to their destination. As with most radios before VHF,
heavy rain and especially lightening caused static that made it
difficult to distinguish the A’s & N’s.
The Beam, or Airway, contained three areas of
interest to the pilot, (i.e., Left of course-On course-Right of
course.). The pilot could identify those areas by the use of the LF
radio receiver, and a set of earphones. He would navigate along
the Airway by listening to the signal being formed by the transmitter.
If the aircraft were located on one side of the
three degree wide beam, the pilot would hear the Morse code letter “A”
(Dit-Daaah) in his earphones. If he were on the opposite side of
the beam he would hear the letter “N” (Daaah-Dit). And if he were
directly on the beam, right in the middle, the combination of the
letters produced a steady tone (Daaaaaah). The pilot would fly
outbound on a single airway until he could not reliably hear the
station anymore. Then he would tune in the station in front of
him and use it to continue on his way. Staying on the beam often
required changes in the aircraft’s heading to compensate for variable
crosswinds. Directly over the transmitter there was an area known
as the “Cone of Silence”. This was an area where the signal faded
out completely. Later, a 75 mhz. Z-Marker was located in the cone
of silence to give the pilot a second way to determine the cone.
It emitted an aural signal, and lit a light on the instrument panel to
let the pilot know when he was directly over the cone. That provided an
accurate fix. The same 75 mhz xmtrs. were sometimes placed across
one or more legs of a range near an airport to provide accurate fixes
for an instrument let down to the airport. They were called Fan
Markers because of their fan shaped area. An aural Morse code
dash, and a light on the pilot’s instrument panel identified
them. A fan marker on the #1 leg emitted one dash every few
seconds, # 2 leg 2-dashes, etc
Over time these LF radio stations and their “Beams”
were scattered all across the nation. Pilots could takeoff in
marginal weather, and not see the ground again until they were at their
destination airport hundreds of miles away. These same beams were
used to create Instrument Approaches Procedures to the runway.
This allowed an aircraft to safely descend on instruments to a point
maybe 500 feet above the ground, and in a perfect position to make a
visual approach to the landing runway. It was a dramatic step forward
in aerial navigation, and remained in use up until the mid 1950s.
In the early 1950s an even more advanced achievement
was made in aerial radio navigation. As the new stations were
added, the old ranges were decommissioned. For a time both
systems were in operation at the same time. By the mid 1950s it
became readily apparent that the nation’s pilots much preferred the new
system as apposed to the LF Range system. Soon all
commercial and light aircraft were upgrading their radio navigation
equipment to the new system.
I can remember when in about 1957 my uncle Glenn
Gash had to postpone a cross-country flight from Renton, Washington, to
his hometown of Colusa, California, because the new radio installation
had not been completed in N4036V, his Cessna 170. I can still
remember him telling us about how easy it was to use the new system to
navigate with on the six hundred mile cross-country flight through
three states. Upon his arrival he couldn’t wait to show us the
new “V” shaped antenna mounted on top of his vertical stabilizer, and
the new Narco radio mounted in the instrument panel. The new
radio, though tube type and bulky by today’s standards, had a little
handle that was turned so that the pilots could tune in any VHF radio
signal. This included communications and navigational
signals. Another knob on the face of the radio allowed the pilot
to control or select what frequency he wanted to transmit on.
The radio was a giant leap forward for the light
plane driver, but it did have some drawbacks as well. The
transmitter was crystal controlled, and the crystals had to be
installed before a flight by a radio technician. It could only
hold about six or eight crystals at a time, meaning the pilots could
only transmit of a channel that he had previously had a crystal
installed for.
This new system was called the VHF Omnidirectional
Radio Range or “VOR” for short. The VOR also used ground based
transmitters to send out a signal by which an aircraft could track an
Airway, accurately determine his position, or even make an instrument
approach to the landing runway. In addition to the high accuracy
of the VOR system, a feature of a ‘Naval Omni’, called Distance
Measuring Equipment “DME” was added to the VOR’s. For the first time
ever, the pilot could in an instant, and for every instant, have a FIX
presented in one instrument. It continually gave one’s bearing
and distance from a known point on the earth. VOR was much
more reliable and comfortable for the pilot to use. He no longer
had to wear earphones to listen for the signal from the ground
station. Now he could simply look at one instrument in the
cockpit to stay on course. And, station passage was just as easy
to identify. The story “The Bishop Convair” refers to the Bishop VOR in
its Flight Planning.
VOR navigation still used the familiar Airways
system, but now the pilot was not restricted to a single beam to
track. Now he could actually dial in and track any one of 360
Radials (a very narrow Beam) from each VOR station. The basic principle
of operation of the VOR is very simple: the VOR facility transmits two
signals simultaneously. One signal is constant in all directions, while
the other is rotated about the station. The airborne equipment receives
both signals, looks (electronically) at the phase difference between
the two signals, and interprets the result as a bearing “TO” or radial
FROM the station.
Interpretation of each Radial is made by reference
to an instrument on the instrument panel in the aircraft. Each
instrument has basically three functional parts. The Omni Bearing
Selector, (OBS) is a knob used to rotate a dial, which selects the
desired radial to track. The TO-FROM Indicator indicates whether
you are tracking TO the station, or away FROM the station. If a
red flag appears instead of a TO-FROM indication, this means that the
station is not being received with sufficient strength to be reliable,
or is not being received at all. The last element is the Course
Deviation Indicator, (CDI). The CDI is a pointer mounted
vertically in the center of the instrument that swings left or right
depending upon which side of the selected Radial (Beam) you are
currently on.
Navigation to a VOR station is relatively
simple. The pilot first determines the radio frequency of the
station he wants to use. Then tunes his radio to that frequency
and identifies the station by listening to the Morse Code
Identifier. Once he is sure he is tuned in to the station
desired, he then rotates the OBS until he gets a “TO” indication and a
centered needle on the instrument. At that point the radial he is
currently on is then displayed at the top of the dial. All he has
to do is turn the aircraft to that heading and fly to the
station. He can use the same procedure to track an Airway.
The needle will tell him when he drifts a little off course due to the
winds aloft. One part of the instrument face has a digital
counter for DME. The numbers indicate miles from or to the
station. Check the number displayed and the clock; one minute
later recheck the counter and you have your miles per minute of ground
speed. Had DME been available to the crew of “The Bishop Convair 440”,
they could have easily followed their departure instructions to remain
within 2 miles of the airport boundary until a safe altitude of 8,000
feet had been obtained.
Most aircraft are equipped with dual radio
receivers, and thus can tune in two VOR stations at the same
time. This makes it very easy to determine location, or finding
an Intersection. An “Intersection” on an airway is a point where
two different radials from two different VOR stations cross. On
the Navigational chart they are identified by two little crossed arrows
pointing to the station being used to form the intersection. They are
further identified by a name containing five letters. Some name
examples are: TURLO, DOYLE, and SCAGG, etc. The Airways are
referred to as “Victor Airways [for VHF], and are identified on the
chart as V-23, V-25, or V-105 and so forth.
The story “Gambler Special” later refers to V-105 in its flight
planning. V-105 is an Airway running north and south along the
California-Nevada border, and was the route this aircraft was required
to fly by company policy on the return trip to Burbank, California
after a fun filled night in Hawthorne. The route would allow the
DC-3 to safely circumnavigate around the treacherous mountains
bordering the Owens Valley. At the time of this accident the VOR
station at Bishop had not yet been installed. Had the VOR been
installed, this aircraft could have safely navigated down the Owens
Valley from Bishop, and not have ended up as it did on Hogback Ridge.
Another less popular form of aerial navigation
called DF, used the directional qualities of a loop antenna to
determine the bearing to the station. Unfortunately
the loop did not indicate if the station was in front of the loop or
behind it. This problem, called the “180 degree ambiguity”,
required some procedures to solve. Nevertheless it was a step
forward. Soon the DF was improved so that a motor would
drive the loop and a cockpit indicator would point to the
station. Thus the name “Automatic Direction Finder” was applied.
The DF or ADF method of navigation can be used by the flight crew, or
the ground crew, to help a pilot determine his position.
Equipment on the ground or mounted in the aircraft
essentially shows the operator which direction a particular signal is
coming from. In the story of the “Wauhab Ridge B-29” DF equipment
at the ground station in California helped the lost aircrew of this war
weary B-29 find their way to the San Francisco Bay area on the
mainland. The station took repeated “Bearings” on the aircraft
when the B-29’s navigator got lost some seven hundred miles out to sea
while on a ferry flight from Hawaii to the Fairfield-Suisun Army
airfield. Unfortunately this story has a tragic ending for all but the
feline member of the crew. However, it wasn’t the fault of the DF
equipment.
In the air, once a particular station is tuned in a needle on the
instrument panel points directly at the station transmitter generating
that signal. The needle reacts automatically to the incoming
signal. Very early equipment used for direction
finding was not automatic. The operator had to manually turn a
big loop antenna mounted on top of the aircraft until he got a Null, or
very weak signal in his earphones. Then he had to solve the
above-mentioned 180-degree ambiguity problem to obtain a direction to
the station. Later that same loop antenna was mounted inside of a
non-metallic “Football” shaped housing on the outside of the aircraft
fuselage. Today the antenna has been greatly reduced in size, and
is generally mounted on the underside of an aircraft. It is now much
smaller and much more aerodynamic.
Arguably the most famous early DF Loop Antenna was
mounted on top of NC16020. This aircraft was the Lockheed 10E
flown by Amelia Earhart on her attempt to fly around the world in the
summer of 1937. Look at any picture of that airplane and you’ll notice
the big loop antenna mounted directly over the cockpit opening.
Unfortunately she was unable to use her equipment to obtain a bearing
on Howland, which was to be her mid-Pacific fuel stop. The rest is
history, and one of the last century’s greatest aviation
mysteries.
When ground stations use their equipment to help
locate the position of an aircraft while it’s in flight, it requires
two different stations getting a bearing on the same signal being
transmitted from the aircraft. Where these two bearings cross on
a map is the location of the aircraft when the bearings were
taken. This procedure is seldom if at all used today. But
in the early days of long over water flights it was the only way,
except for Celestial Navigation, for an aircraft to determine its exact
location while over the water. Of course Dead Reckoning was used
in between Celestial shots.
ADF equipment is still used on every Instrument
Certified (IFR) aircraft today. However, it is generally no
longer used as a primary form of navigation. Its primary function
now is to point to and identify the Outer Marker (OM) or
Non-Directional Beacon (NDB) on an Instrument Approach to
landing. There is also a Non-Precision approach procedure
available at many large airports that utilize these same beacons to
help an aircraft find the airport in IFR weather.
Another unique ability of the ADF equipment is its ability to receive
all broadcast stations within range. A broadcast station is your
everyday run of the mill commercial radio station. It can also be
used to get a bearing, and as an aid to finding an airport that does
not have any other electronic guidance. The same stations you listen to
in your car to get the latest baseball scores, get the latest news, or
listen to your favorite music, could be a lifesaver.
However, I don’t recommend using the ADF in an aircraft for purely
entertainment listening purposes. If you’re at the controls of an
airplane you need to be thinking “airplane”, and not baseball, or
mentally arguing with some talk show host like Rush Limbaugh.
Using a regular commercial broadcast station for
aerial navigation was widely used in the early days of radio
navigation. Now days with all of the modern technology available
to the pilot, DF navigation is rarely used. On early
navigational charts the location of the broadcast antenna was
identified with the station’s call letters, the height of the antenna
above the terrain, and the height of the antenna above sea level. If a
pilot was not sure of his position, and thus not quite sure where the
airport was, he could “home” in on the nearest broadcast station, and
then after station passage, take up a heading to the airport from
there. It was a perfectly safe and widely used method at the
time. I have in my collection a VFR navigation chart from
1957. On that chart all of the more powerful radio station
antennas are shown in the above-mentioned format. However, later
charts have dropped this form of broadcast antenna identification.
The fact that the needle on the ADF indicator points directly to the
antenna emitting their signal, and not necessarily to the city where
the station is actually located could get the unwary pilots in
trouble. As an example, in Merced, California the studio for the
most popular radio station is in downtown Merced. But their
transmitting antenna is actually located some 8 miles northeast of the
city, and on flat farmland. To the south about 50 miles,
the antenna for a popular station in Fresno is located some twenty
miles to the southeast of the city, and in close proximity to rapidly
rising terrain. If in bad weather you were “homing” on their
station’s signal, and descended to the pattern altitude of about 1,200
feet while looking for Fresno, (which is only about 336 feet above sea
level), you would most likely hit the top 78 feet of the antenna, and
never see it coming. The last thing you would see would be the
big red light on top of the antenna flashing in the center of your
windshield. This would not be a good thing!
The latest form of navigation to be approved for use
in aviation is the GPS system. There are no stories in this book
of aircraft using GPS navigation, so its description will be very
brief. GPS navigation is a form of Celestial navigation. It
also uses heavenly bodies in the form of man-made satellites instead of
the sun, stars, and planets, to plot a position. It stands for
Global Positioning System. Rather than angles, GPS determines
ones position from the time it takes the signal to travel [thus the
distance] from any 2 or more of the more than 24 satellites in special
orbits above the earth. Since the speed of light, including radio
waves is accurately known, visual sight of the satellite in
unnecessary. It works 24 hrs a day, and is not affected by poor
weather that restricts visibility. The only requirement being reception
of the signals. Since airplanes do not normally fly into tunnels
or inside of steel buildings, they are always “in range”.
Amazingly, the special equipment necessary to use it properly can fit
in the palm of your hand. And all of the difficult mathematical
computations necessary to figure out where on earth you are is now
figured out for you, and updated every few seconds anywhere in the
world. How neat is that?
In an earlier book, which I co-authored with
well-known aviation wreck chaser Gary P. Macha, “Aircraft Wrecks In The
Mountains And Deserts Of California” (3rd edition), there is a detailed
description of how I used a hand-held GPS unit to find the long lost
crash site of ”The Hobart Mills C-47”. In that story I mention
that a modern handheld GPS unit, weighing less than a pound, could
eliminate more than three-hundred pounds of then (1940s)
state-of-the-art radio equipment and instrumentation, while at the same
time giving the pilot more information about his position,
altitude, ground track, and speed than all of that equipment
combined.
My personal GPS unit is one of the most important
pieces of equipment I use when I’m searching for a crash site, or just
plain driving on a cross-country road trip. In the days when GPS
was new or still not well known to the general public, only the
military had such receivers and could use its features. Now
anyone can purchase the latest GPS receiver model at the local sporting
goods or discount store. Even automobile manufacturers are offering
them as standard equipment in their newest model cars.
Most models come standard with a basic mapping
program already installed. But to take full advantage of all that the
GPS unit can do for you, you’ll need to interface it with your personal
computer. You can purchase stand alone mapping programs that can
be installed on the home computer or Laptop to create waypoints, routes
and maps, and then download that information directly into you
hand-held GPS unit for field use. A Waypoint is an electronically
“Marked” point on the earth’s surface that is defined in your GPS unit
as a set of numbers, referred to as coordinates. My unit is a
Garmin GPS III+, and I use both Mapsource, and the TOPO GPS mapping
program from National Geographic when doing my research.
Not only can you find and create Waypoints to help in your searches,
but you can actually track where you’ve been in the field as
well. Perhaps the most valuable feature for me is the tracking
feature. As long as the unit is turned on and set up for tracking this
feature actually keeps track of where you’ve been as you are searching
an area. At the end of the day you can upload that information to
your PC, and save it as a file for later reference. How cool is
that?
Finding one’s position with the GPS is simple and
automatic. All you do is turn the unit on, and allow it to
acquire (electronically find) the appropriate satellites. In the
newer units this only takes a few seconds at best, but can take up to a
full minute or so depending on location, canopy cover, and age of the
unit itself. Once the unit has locked onto and is receiving
satellite signals it automatically displays your current position and
altitude in your choice of formats (i.e., longitude and latitude, or
UTM, feet or meters). It will also display your speed if you’re
moving. It will even show you where you are on a moving color
map. What could be easier?
GPS navigation is widely used in aviation today, and
has made all other forms of navigation somewhat antiquated.
However, for the average light plane driver VOR and Pilotage are still
the most commonly used forms of navigation. GPS units approved
for
use in aircraft are somewhat expensive. The reason they are expensive
is because varying conditions of atmospherics change reception times
that cause the GPS to be up to a hundred or more feet inaccurate in
any, or a constantly changing direction. Not a problem in
navigating airways, but not accurate enough for instrument approaches
to minimum approach altitudes, nor for the land surveyor.
The fix is called Differential GPS. It
requires placing a GPS
with a VHF transmitter over a spot that has been meticulously surveyed
over time to ascertain its location to a centimeter! The GPS then
computes the difference between its received position and its known
position, and then transmits the correction to all GPS’s (with the
special receiver) in the area. Each GPS then has the same centimeter
accuracy. This system is used for GPS approaches.
So even if not every light plane has a GPS system
installed, many civil
aviation pilots will still carry a smaller hand-held unit with them
when on a cross-country trip. These non-aviation approved
hand-held units can be very useful, but somewhat dangerous if they are
the sole means of navigation utilized. These units were designed
for land navigation, and not aerial navigation. They do not show
information critical to a pilot in flight such as Airways, Restricted
areas, and designated airspace.
Even today’s automobile manufacturers are beginning
to install GPS navigation systems in the automobiles and trucks as
standard equipment. Home offices for the long haul truckers can
now keep track of their vehicles on a minute-by-minute basis as they
travel from coast to coast. That round white bowl you see on top
of the truck’s cab is an enclosed GPS and telemetry antenna sending
information back to the home office via satellite.
So there you have it. An over simplified
perhaps, but basic
explanation of aerial navigation, and how it has evolved over the years
to make flying safer for pilots and passengers alike.
Copyright 2007
by Don R. Jordan