Contents:
Very-high Frequency Omni-range (VOR);
...VOR Procedures; …Flying
the VOR Step by Step; ...VOR Lesson;
...VOR Lesson Diagrams; ...VOR
STEPS; Flying from a VOR to intercept
a radial; ...Finding Position by VOR radials;
Where am I?; ...Time
to fly to a VOR; ...Half Angle Wind Correction;
...Distance Measuring Equipment; ...Poor man's DME; ...VOR
Disorientation Lesson; ...Using Global
Position System (GPS); GPS procedure;
GPS and Situational Awareness; ...The negative side of GPS; ...LORAN;
...HSI; …Weather
use of ADF; …Navaid Unmonitored;
Very-high Frequency
Omni-range (VOR)
This system is now over 50 years old and will eventually be replaced by the global positioning system (GPS). VOR information only tells you of the VOR radial you are on and which way to turn to get to a specific radial. Situational awareness using the VOR requires considerable training and attention to detail. The most neglected detail is referencing VOR indications to the compass/heading indicator indications.
Your VOR receiver determines position by comparing the phase (time) difference between to different parts of the VOR station signal. One signal is sent out in all directions, line-of-sight much the way an airport beacon sends light. The second signal is used to time the first from north. The Tacan (military) part of a VORTAC is mechanical rather than electronic but nine-times more precise than the civil system. The carrier wave of the signal is coded in a three letter Morse Code identifier. Your knowing Morse Code is a good plus. The Code is at about eight words a minute, which is slow enough for beginners. Some VOR have duplex communication capability. This means that you can talk to a Flight Service Station (FSS) on 122.1 from your radio's com side and hear them talk back to you on the VOR frequency.
At 30 miles from a VOR slight out of tolerance and an OBS off by the allowable 4° you could be 4 nautical miles off the centerline. At best, even with the needle centers from a VOR you are seldom where you think you are. At six miles from a VOR and the needle centered you could be off nearly a mile; at ten miles the error is 1.2 miles. None of these allow the possibility that you mis-set the OBS by a degree. A field that has the VOR centered on it shows 200' error with one dot deflection at the half mile airport boundary. At twenty miles you could be over a mile off the line and still have the needle centered.
You will frequently note that VOR radials, while apparently in a straight line through the VOR, will have differing numbers than would be reciprocal. The lines are using the great circle route that change direction with longitude. Additionally, differences in magnetic variation make for the different numbers.
Aside from an initial introduction to the use of the VOR during a flight from Rio Vista to CCR I make a practice to minimize VOR instruction. I have found that reliance on VORs reduces the efforts of a student to pay attention to terrain and area features. In the real world of emergencies the use of a VOR at any appreciable altitude is very unlikely in a radar environment. In this same world, the use of a VOR at low altitude is very marginal and capable of flying you into intervening terrain. It is essential that the VOR user be knowledgeable as to the altitude and line of sight restrictions to a given VOR. In mountain areas, a VOR may be unusable in certain directions beyond 20 miles regardless of altitude. The Airport/Facilities directory gives this information. Look up CCR VOR.
During the cross-country training phase I teach the use of a VOR radial as a backup to a checkpoint. I minimize this and other uses of the VOR and select flights that are "rich" in visual checkpoints. I feel that over dependence on VOR navigation is likely to cause future problems. VORs fail and are sometimes out of service. This is always at the most inopportune times such as during bad weather or reduced visibility. Skill in pilotage can be taught. It improves with use and is the most reliable last resort of navigation. Knowing where you are is a unique kind of brain food. Just note how poorly the brain functions when you are lost. It is unwise to rely on a device that may lose capability at just the wrong time.
Unfortunately, the average VOR user just sets the frequency and the OBS. Good practice recommends that you check the Morse code identifier every time you use the station. Some pilots keep the code on at a low level as an additional precaution. Most pilots seem to not identify. Such a practice will eventually bite you and it will be at the worst possible time. Besides, if you are lost your brain will have stopped working and you will not use the correct and proven procedures. Use of the steps to good VOR navigation requires constant practice. I teach the complete VOR process only during the proficiency phase of instruction.
The essential of good VOR tracking is accuracy of settings and precision of headings. Since the OBS is in divided into spaces of 5 degrees, such as 340 to 345, it is difficult to set 342 and 343. Just centering between the marks is the best choice. It is possible to track to or from a radial without an accurately set Heading Indicator. However, it is much less confusing to judge the wind if the H.I is properly set. The ability to fly and hold headings both VFR and IFR is gradually acquired. Once acquired, it makes flying the VOR or Localizer relatively simple and a no-brainer. It does take practice. Fly the heading, not the needle.
Flying TO a VOR is much like trying to guide a ball with a stick between two very long boards placed at a 20 degree angle. The idea is not to let the ball touch either board while moving it toward the vertex. You may weave some at the very beginning but it is important that as the angle narrows the precision required greatly increases. Inversely, if rolling the ball from the vertex the ever-widening space makes keeping the ball relative near the centerline becomes easier. This analogy very aptly explains flight TO and FROM a VOR. The full deflection of a VOR needle pegs out at 10 degrees to each side. That of the Localizer does so in 2.5 degrees it is four times as sensitive.
The course reversal used in ground reference can be used effectively in practicing VOR tracking. Find an isolated VOR that will allow legal flight below 1000' and track directly into the wind to the VOR and then two minutes from it. Perform a 90/270 course reversal and during the 270 part reverse the OBS and track inbound again. Do this several times and then do it with a 90-degree cross wind several times. A good study of needle action is to fly a rather large circle around the VOR with a few steep 360s every 90 degrees. Don't change the OBS until you get back to the initial point.
Two specific regions of flight near a VOR provide unreliable signals. The most common area is the cone of confusion that projects upward from the VOR. As a cone its zone of confusion becomes greater with altitude so that you can get rather precise TO/FROM reversal as below 1000' but at three thousand feet and higher it may take twenty seconds or longer.
The second region exists to both sides of the VOR in 20-degree fans as determined by the OBS setting. If the OBS is set to 360 and the flight transitions the VOR area on a 360 heading toward but to the left or right of the 180/360 radials you will fly through a region of ambiguity. This region extends from the VOR to the sides in a 20-degree fan. Approaching from the south you will have a FROM reading until reaching either the 260 or 100 radials. Inside these radials the TO/FROM will waver back and forth until it changes to OFF and then to FROM on exceeding the zone fan at the 280/080 radials. This can best be understood by drawing it out over a VOR compass rose.
The VOR indication is according to the aircraft position relative to the station, not the heading. If there is disagreement when flying through a VOR (TO or FROM) between your heading number and the heading indicator as set with the compass you will experience "reverse sensing". With 'reverse sensing' flying toward the needle just makes it go further from the center. Once the needle is at full 10-degree deflection you can no longer detect reverse sensing.
One of the major difficulties with the VOR is in interpreting ATC directions for what you are to do relative to radials. Radials begin at the VOR and extend out from the station. ATC always names the radial from the VOR. Use the reciprocal of the radial if ATC includes the term 'inbound'. If an intercept is expected they will usually include an intercept heading. This is true whether they want to fly to, from, or intercept. The problem mainly exists when the pilot confuses bearing and radial.
One thing to understand about a VOR, it does not read differently
as you turn the airplane around in a tight circle (assuming you
are 30 miles from the VOR). Another way of saying it, is, the
VOR doesn't care which way you are heading.
There are four modes of the VOR head and airplane direction.
1. Flying towards the station with a TO flag (Normal sensing)
2. Flying away from the station with a TO flag. (Reverse sensing)
3. Flying away from the station with a FROM flag. (Normal sensing)
4. Flying toward the station with with a FROM flag. (Reverse sensing)
Most ATC and charts use FROM radials. Tell an ATC guy that you
are on a TO heading in identifying your location and they get
confused.
Second Opinion:
The VOR Receiver quite simply is incapable of reverse sensing,
any reverse sensing that goes on is in the mind of the interpreter.
The VOR receiver is a dumb machine and does what it is told. If
the aircraft is on a heading of 090 and the person using the VOR
inputs a heading of 270 the VOR correctly interprets this as if
the plane were heading 270 and gives corresponding course corrections
that are accurate for the situation. This type of situation arises
usually in conjunction with holding .
Flying outbound in the pattern to intercept the holding course
inbound. If the inbound course is i.e.. 270 the outbound in no
wind conditions is 090 the OBS is set to 270 and you are to the
090 radial. The CDI indication would be a left needle deflection
which would be correct if you were flying 270 which is what the
pilot told the VOR. In other words the needle does NOT
tell the pilot which way to turn , it indicates which way the
selected course is from your present position. In the case of
the holding pattern if the pilot stopped his actions on a heading
of 090 what would be the shortest direction to turn to intercept
the 270 course( 090 Radial) You guessed it ,turn right even though
the needle showed a left deflection , This is not a case of reverse
sensing on the instruments account. Try this exercise and look
at the relationship of the DG and the OBS,CDI indications. Do
you notice the 45 degree hack marks on the DG ? They help with
interpretation and course intercept.
R.Wallace CFIAIM
Flying
the VOR Step by Step
---Crossing the VOR, you should initially parallel your new
course before planning your intercept.
---A radial is always FROM.
---Fly THROUGH rather than TO.
---Always check your VOR accuracy.
---You can only track a VOR radial if you can fly a heading.
---Fly your needle within a needle width.
---Nibble at your heading corrections to keep the needle centered.
---Large heading changes should never be required to keep the
needle centered.
---Large heading corrections will only be required at low airspeeds.
--- It takes a direct crosswind of 1/2 true airspeed to require
a 30-degree crosswind correction.
---On station passage
..Note time of passage
..Change OBS
..Turn to new course
..Report to ATC
..Confirm your climb/descent limits.
After a student has read about the VOR and its theory of operation, I like to take a flight of about an hour to actually watch the needle and flag movements as a flight is made in the vicinity of the VOR. The flight altitude is best to be at a safe altitude that is within 3000 feet of the surface. The lower and closer to the VOR that this can be done the more precise will be the needle and flag changes and reversals. To best understand this process you might wish to follow the diagram or the flight as I tried to illustrate it below.
The demonstration that is an exception to this is the 360 turn on a radial. For lesson efficiency this maneuver is best performed more than three miles southeast from the VOR. The needle is centered on a radial that corresponds with the aircraft heading from the VOR, preferably on the 135 radial. As immediate tight 360 is performed. (Station #1) It should be noted that the needle will remain inside the 'doughnut' regardless of the direction of the aircraft. To emphasize the validity of aircraft heading having no relationship to the immediate centering of the needle the turn should be done again in the opposite direction. This concept is important. Everything is not correct just because the needle is centered. Where the intent is to keep the needle centered, the pilot must fly an appropriate heading to keep it centered. Now proceed toward the VOR until about one-mile to the southeast side of the VOR.
Set the OBS to 0 (North) and turn the aircraft to fly due North. The flag will read TO and the needle will be at full left deviation toward the VOR. At the flight proceeds northward to the needle will always full left but when we get within ten degrees of due east the TO will gradually go to RED and then to FROM. Continue North for about a mile and turn quickly to due West. While proceeding west the needle will remain to a full left deflection until you arrive within ten degrees of North. Gradually the needle will move toward the center and then move away to full deflection to the right. This movement is characteristic of approach, interception, and passage beyond any radial that might be used as a checkpoint reference on a cross-country flight. After the needle has moved to full deflection to the right continue again for about a mile and turn due South.
We have deliberately set up a reverse sensing situation. The OBS is set to North but we are heading South. The needle points away from the VOR The TO/FROM flag will give a false indication except when passing within ten degrees of due west, at which time the RED flag will indicate a region of ambiguity. Again at one mile to the south you should turn due East and again the needle will begin to move toward the center when you are within ten degrees of the 180 degree radial and toward the VOR as you pass beyond 180. At one mile out do a 90/270 course reversal and fly the rectangle again in the opposite direction. On completion of the second rectangle try to determine the wind direction from surface indicators or by contacting a nearby FSS.
Now we are preparing to practice flying TO and FROM the VOR with course reversals. Initially we will fly as nearly upwind and downwind as we can. The process begins proceeding upwind. We center the OBS needle and determine that the heading indicator and compass are in near agreement. Proceed to the VOR and note that there is ever increasing sensitivity in the needle movement. Try making small corrections by using and holding the rudder. Once the needle begins to move quickly maintain present heading that you have determined will fly you out of the cone rising from the VOR. The higher you are above the VOR the larger will be the cone and the more time it will take for the needle to settle down on the other side of the VOR. Find a remote VOR if you really want to see how quickly it can reverse from TO to FROM when crossed at a low altitude.
Once the needle has settled down fly upwind from the VOR so as to distance yourself far enough from the VOR to execute a 90/270 course reversal. While in the 270 part of the reversal be sure to turn the OBS needle 180 degrees to the direction you will be returning to the VOR. Since you will be flying downwind now, try to anticipate any heading adjustments by timing the last few degrees of your turn. Correct your heading as needed for keeping the needle centered. If the tail wind is substantial, expect things to happen more quickly. Complete at least two full crossings with minimum required wind corrections before doing the procedure at 90 degrees to the wind.
Flying a VOR radial at 90 degrees to the wind requires that you set the radial into the OBS and after confirming the HI and compass agreement, make an estimate of the heading correction required to keep the needle centered. It is unlikely that your initial estimate will be accurate. You then must make a new heading correction estimate. This estimate will be a specific heading number that you believe will cause the needle to move to the center of the 'doughnut'. If you guess correctly and the needle moves to the center, now you must make another estimate of the heading that will stop the needle and keep it centered. The selection of both the corrective heading and the stopping heading requires repeated practice. Since the process may need to be done more than once it wise to get somewhat further from the VOR before beginning the process. Ideally you will get the needle stopped and have determined the heading that keeps it stopped as you cross the VOR. Even though the needle begins to move and flip quickly, hold the heading until leaving the ambiguity cone. If the needle remains centered as you fly from the VOR, all is well. If the needle moves from the 'doughnut' you must again repeat the process of finding a heading that re-centers the needle and a heading to stop it and keep it centered.
The course reversal in this situation requires that the direction and the bank of the reversal be carefully planned so as to allow you to come out of the turn with a heading correction that will either correct or hold the needle in the 'doughnut'. The sooner you get the needle in the center the sooner you can find the heading required to keep it there. Since you are flying as nearly 90 degrees to the wind only in a reverse direction, very nearly the same upwind correction will work in both directions. If time becomes a factor this last procedure might be delayed for another time.
One very useful exercise to become acquainted with the workings
of the VOR is to 'box' it. By this, I mean fly a square around
the VOR from about a mile away. Select the four cardinal directions
for your 'box' and set in 360 on the OBS. Begin your flight at
the southeastern corner of you 'box' on a 360 heading.
Fly the entire 'box' and watch the way the needle acts. After
completing the 'box' make a course-reversal and go around the
other way. Try to anticipate just what the needle will do this
time around. Use a safety pilot if you can. Otherwise do it at
700' AGL which should be below any other likely traffic.
North, centered needle, Reverse sensing, side, Region of ambiguity,
Region of flag reversal, VOR flag reversal ,
#1 360's on 135 radial
#2 Begin heading North around the two square mile square.
Wind correction angle
Draw in instrument face and needled position and then fly to confirm
drawing.
For a checkpoint For flying to a VOR
1. Set the frequency 1. Set the frequency
2. Ident the code(volume up/down) 2. Ident the code(volume up/down)
3. Set the OBS(FROM ) 3. Center OBS From
4. Confirm that the needle 4. Center OBS To
is on the side toward 5. Turn to heading of OBS
the station 6. Compare, OBS, HI, compass
7. Fly (through) the needle
1. Set frequency either to or from
2. Ident code(volume up/down) 1. Set frequency
3. Center OBS From 2. Ident code(volume up/down)
4. Turn to OBS Heading 3. Set OBS To or From
5. Confirm HI, OBS, compass 4. Turn toward needle on
6. Fly to the needle heading to give 30 to 45
7. You have flown through the VOR degree intercept angle off OBS
setting
5. When needle centers turn to OBS heading/
6. Check OBS, HI, compass
7. Fly to needle
This procedure is best done with two VORs but can, with practice be done using only one. Have your sectional folded so that both VORs are showing. Confirm that you have sufficient altitude for line of sight reception from both. Use of three VORs will give a triangle which should include your location.
Where
am I?
1. Select frequency and IDENT
2. Set OBS CDI needle to center and FROM
3. Draw line from center of VOR compass rose on that bearing
4. Distance may be determined by DME, if available
5. For greatest position accuracy using single VOR fly the course
line in or outbound.
6. Repeat steps 1, 2, 3, and 4 using a different VOR as nearly
90° to your original chart line as you can find and receive.
7. Where the two lines intersect is your position for a moment.
8. Doing steps 1 through 5 with dual VORs can be used to give
you a series of positions and a flight line with wind effects
without recourse to compass or E6B.
9. You are (were) at the point of intersection.
10. The longer this procedure takes the more you must figure into
present position your airspeed and course.
11. A third VOR will usually form a small triangle of position.
Time
to Fly to a VOR?
Simplified it requires only that you locate yourself on any
VOR radial. Turn to right angle to that radial and time the number
of seconds it takes to intercept a radial 10 degrees further ahead.
Drop the last digit from the total number of seconds.
The remaining digit(s) is the number of minutes it will take you
to track to the station. No wind factored in.
Determine your radial on a VOR. Fly at right angles to that radial. Determine what radial will be 10 degrees ahead of your present radial. Set the OBS for that radial. Time in seconds how long it will take you to fly across the 10 degrees. Drop the last digit of that time. The remaining digits are the number of minutes it will take you to fly to the VOR without regard to wind. This should be practiced several times before you can rely on your figures.
Set in any radial from a VOR. Turn 90 degrees to that radial
and take a time hack. Reset the OBS to lead your aircraft by 10
degrees. The number of seconds divided by 10 that it takes you
to center the needle at the new OBS setting is the number of minutes
(disregarding wind) it will take you to fly to the VOR.
1. Turn to right angles of the CDI centered course line and start
timing in seconds.
2. Fly in this right angled direction until CDI has moved 10°.
3. Note time to nearest ten seconds. Drop the zero.
4. The remaining number is how long it will take you to turn and
fly directly to the VOR without considering the wind.
Opinion
The question is a deliberately simplified application of the one-in-60
rule with the special rule-of-thumb case for 10 degrees. I think
any CFI applicant who can't recognize a question based on the
1:60 rule doesn't have a full understanding of the art.
(The rule is that a one degree deviation makes the legs of
the triangle about 60:60:1. For small angles you can simply multiply,
so 10 degrees is 6:6:1. Hence 8 mins becomes 48 mins. 130kt is
2 miles a minute plus about
10%.)
I feel that it's important to be able to do this kind of mental arithmetic, even if you argue that (a) any time you're in the situation described, you're going to have DME (b) by the time you've remembered the 60:1 rule and done the right multiplication's you're in the next state.
Half Angle
Wind Correction
The process of correcting for wind when flying a VOR or Localizer
is similar to the guessing of a number between 1 and 30. The better
you guess the correct heading to compensate for wind the fewer
adjustments and guesses required. Even in strong winds a 30-degree
correction will bring in a needle. Once the angle of heading required
to bring in the needle has centered the needle, a new guess is
required to select the heading that keeps the needle centered.
Half angle method begins with the aircraft heading, OBS, and compass
in agreement either to or from the VOR. As the VOR needle moves,
say to the right, it is showing that the aircraft is moving to
the left of the selected radial. The pilot now must make the first
of his guesses. From estimates or forecasts he chooses a heading
no more than 30 degrees of intercept that will bring in the needle.
Once the needle is centered a second guess is made that may keep
the needle centered. If once again the needle moves off center
another pair of guesses is made. Even the worst 'guesser' who
begins with a 15 degree WCA (wind correction angle) should require
no more than three pairs of guesses to keep the needle centered.
Be aware that winds do change so that even a WCA that works from one checkpoint may not work from the next. Changes of altitude can have the same effect. It is important that the pilot realize that the four times greater sensitivity of the Localizer than the VOR requires greater concentration to selection and heading holding. The basic process remains the same, however.
DME can give erroneous readings. This means in addition to the normal slant range errors. Remember DME will read 5000' as one mile from the VOR. Using the Pythagorean theorem we find that at three thousand feet and a DME reading of one-mile (5000') we are actually only 4000' from over the station. At four thousand feet and a one-mile reading we would only be 3000' from over the station. The closer we are to the station the greater will be the slant range errors of speed, time and distance. The DME should be crosschecked with LORAN or GPS, another DME, a VOR cross bearing or a known geographical point for accuracy. LORAN and global positioning system (GPS) do not have slant range errors inherent in DME.
A high pitch identifier every third or fourth time the navaid
identifier is heard can confirm DME operation. If the navaid is
out of service the DME identifier will be heard every 30 seconds.
6076 feet per nautical mile
5270 feet per statute mile
806 feet difference
If you are flying to a VOR without DME, it is possible to utilize a second VOR as an arrival aid. The requirements are that you must be able to receive the second VOR and know the radial OBS setting from that VOR. Try to get as near a 90-degree angle as possible.
The procedure requires that you set in the #2 frequency, ident, and set the OBS to read FROM the #2 to the #1 VOR. By noting the movement of the #2 needle you can determine your arrival over the #1 when the needle centers. This also makes it possible to plan a leading turn to another radial before actual arrival.
Instructor or examiner may have student put head down and close
eyes. During this period the heading indicator is rotated at least
90 degrees. Student is then give a frequency (unfamiliar) to set
the VOR and is told to track to the VOR. Unless the victim immediately
goes through the process of confirming the correspondence of the
compass with the heading indicator, nothing will work as it should.
Disorientation occurs. This is even worse if
it is done under the hood.
The accuracy of GPS is unsurpassed. Newer installations have
the ability to measure their degree of accuracy by giving an estimated
position error or EPE. It is the programming of the system by
the pilot that poses potential problems and dangers. The system
software is relatively complex to program. This is especially
true for the computer illiterate. GPS will replace all ground
based navigational systems and LORAN. The latest improvement to
GPS is a wide-area augmentation system (WAAS). IFR approaches
will be possible to any airport with accuracy within seven meters.
The Navstar GPS is a constellation of orbiting satellites (24
+ 2 reserve) providing navigational data to military and civilian
users around the world. Provides 24-hour services. These include
accurate three-dimensional (latitude, longitude, and altitude)
velocity and precise time, passive all-weather operations; continuous
real-time information; support to an unlimited number of users
and areas; and support to civilian users at a slightly less accurate
level. The signals are so accurate that time can be figured to
within one-millionth of a second, velocity within a fraction of
a mile per hour, and location to within a few feet. Except for
GPS and LORAN all other modes of electronic navigation degrade
in accuracy as distance from the station increases.
GPS as used by civil aviation has a built in inaccuracy to
prevent bad-guys from targeting the U. S. Civil limits are about
100 meters with 99% assurance as compared to within one foot for
the military. Military signals are accurate so that time can be
computed within one-millionth of a second, velocity within a fraction
of a mile. This variation of accuracy is called 'selective availability
(SA). With SA you are assured of 20-meter accuracy 50% of the
time and 75 meters almost always. Groundspeed error in a hand-held
GPS will be less than two knots. With SA off the error is less
than one knot. The system has 24 satellites circling at 7500 knots
at 10,898 nautical miles high. They complete an orbit every 12
hours while continuously transmitting their position. They are
line of sight but each satellite can see 40% of the earth. When
a GPS receiver locks on four satellites a multi-dimensional fix
is possible. GPS satellites get new data every hour. Receiver
Autonomous Integrity Monitoring (RAIM) checks the minimum signals
required for a fix.
The military has the capability of distorting the GPS signal to
prevent use of the system against the U. S. When distorted, the
signal would not be useable for navigation.
The FAA has contracted for 35 ground based wide-area augmentation system (WAAS) to improve error detection, 7 meters accuracy and availability. By the year 2000 GPS will be the only aircraft navigation system.
GPS is going to change the way instrument navigation and approaches are flown. Every runway can have a straight in approach. Alternate arrivals will be easily possible. There is no VOR cone of confusion or DME slant range errors. The course deviation indicator (CDI) can be programmed for scaled deviation according to use for navigation, non-precision, or precision use. GPS can be used to confirm information from heading indicator, altimeter, airspeed indicator, VOR, ADF or DME. During airport arrivals or approaches the GPS can even show the runways. You can fly a serpentine river with a properly programmed GPS. With GPS as an aid you will be able to locate an airport eight times more quickly and accurately than a pilot without GPS.
In October of 1994, Stanford research showed that a small and
inexpensive addition to the surface of any runway and to the aircraft
could allow accurate landings at any airport and any runway. Accuracy
was to within one inch of location and altitude. It was tested
with 110 landings. A processor on the plane compares GPS signals
to those of the runway transmitter to give relative runway position.
Aircraft instrumentation remains the same in function and appearance.
In 1995 Category 3 level instrument approaches have been flown
using differential GPS systems. This requires a local ground-based
GPS antenna that allows correction of GPS errors. The accuracy
of the differential system is within one foot.
The moving map indication makes situational awareness less of
a problem since the active waypoint, the track and next waypoint
can be mapped as well as altitude minimums. How well any of this
can be done depends on the installed database. We are well on
the way to a paperless cockpit.
I recently flew from CCR to YUM non-stop. This is a straight-line distance of 485 nautical miles. I had forecast 33Kt tail winds for the route at 9,500'. Under non-GPS conditions I have always stopped at BFL for fuel. This time I made BFL in 1.5 hours and my GPS said that I could make YUM with VFR reserves. For the remainder of the flight the GPS kept me advised of ETE so that I could manage my fuel in case tail winds did not continue.
I would recommend that a handheld GPS be considered in preference to Panel installed. In the event of total electrical system failure or emergency landing in an isolated area, the handheld GPS can become a very useful aid. A recent 1994 development allows the placement of a GPS transmitter on the runway surface that will allow precision landings regardless of aircraft type.
If your aircraft has GPS or LORAN you will be expected to be able to use it for navigation and emergency purposes. You should be able to get time, speed and distance information. The student should be trained in programming, and storing flight plans, waypoints and direct operations. Later skills in airport information, nearest-airport, airspace, malfunction, and emergency use should be covered. Additionally you will be expected to be able to navigate without GPS by using other traditional aids. This means a student must be competent in the use of the sectional, VOR, E6B, and approximate headings as required by the Practical Test Standards. Special emphasis should be make regarding pilotage, since GPS and other aids tend to reduce skilled and practiced usage of surface orientation. A further warning is that GPS is under military control. At any time they may use GPS jamming procedures that will cause your GPS to give errors of 20 miles in course position, thousands of feet in altitude and 20 percent errors in distances and speeds. A VFR GPS, unlike an IFR GPS will not have a receiver autonomous integrity monitoring RAIM ability. This means in a VFR GPS you will have no way of knowing about the error unless you have used other aids, including pilotage, to maintain positional awareness.
GPS signals can get occasional bad signals or electronic interference
that cause inaccuracies. IFR units have RAIM--receiver autonomous
integrity monitoring--that warns the user that inaccuracies exist.
In an aircraft, the use of any of the following frequencies may
cause GPS problems. 121.15, 12l.175, 121.200, 13l.250, 131.275,
and 131.300. GPS can be used if it does not interfere with any
radio frequencies (See AC 80-34 for frequencies).
A DME site that is not in your GPS data base can be used by calculating
a distance from any fix that is on the same course and maeasures
from the same source as your unnamed fix. Use of the GPS from
the airport reference point, usually near the middle of the airport,
means that you must calculate for end of runway according to its
length. No existing GPS has the required 'integrity' that exists
in present VOR and ILS components. No existing GPS equipment is
upgradable to LNAV. GPS greatest negative is cost of data bases…NOS
is considering providing data bases.
GPS handheld must be put on aircraft without tools.
Current accuracy 329 horizontal and altitude 460' + 780'
WAAS will give non-precision approaches to military criteria in
2002
EWAAS is extension of WASS in 2002 300' and 1/2 mile accuracy
LNAV is stand alone GPS that requries short range ground facility.
The GPS system requires a computer than is capable of receiving
both user and satellite input. The user is required to do only
five things to the GPS for an IFR approach:
1. Select an approach
2. Set up approach
3. Set up course reversal if required
4. Enable the approach within 30 miles of destination
5. Confirm RAIM is available
6. Start the missed approach
7. Enter complete flight plan into GPS before takeoff
Flying
1. Pilot should be able to accept vectors
2. Fly holding patterns
3. Keep the needle centered
4. Descend at waypoints (timing)
5. GPS Emergency Approach Lesson:
This could be programmed as a VNAV that will activate automatically.
1. Fly initial approach above pattern altitude at right angles
to selected runway directly over the Airport Reference Point.
(ARP). If able fly entire distance at distance at approach speed.
2. At .6 GPS of a mile from the ARP, execute turn to downwind
and descent to pattern altitude while flying downwind until GPS
reads 1.3.
3. Turn base and initiate descent to pre-determined MDA but not
lower than 500' of threshold height
4. Turn final after having flown 1/2 or 1.3 GPS of ARP. Angle
with shallow turns toward runway so as to fly directly to ARP.
GPS
and Situational Awareness
GPS is soon to be a part of the Practical Test Standards.
The test is surely to include a pilot's ability to transition
from GPS awareness to supplemental electronic awareness to pilotage.
This transition is probably more important to the IFR pilot.
The GPS is usually the first introduction the average private pilot has to the 'glass cockpit'. Use of the GPS breeds dependence. In a low workload flight GPS and similar aids are very handy and easy to use. In a high-workload situation the complexity of the procedures is apt to get the pilot so involved that he falls behind the basics of flying.
A pilot should use only the instrumentation of the conventional
cockpit when hand flying the aircraft. Coupling the autopilot
and GPS puts an additional load on the situation since all performance
must be verified by more traditional instruments. I
suggest that just a much time be spent flying by hand as by use
of the 'glass cockpit. Rusty dead reckoning skills derive
from use of the GPS
1. Most GPS displays are polarized. A pilot wearing polaroid
glasses must hold his head horizontal to read the GPS display..
2. Certain letters and numerals can be confused one with the other.
Give every display the test of reasonableness. Does my direction
and distance make sense. Every time a new satellite is put into
orbit your GPS will require some time to get it into the database.
Newer IFR units have a Receiver Autonomous Integrity Monitor (RAIM)
which will send an ERROR message if there is a problem.
Should you ever have the experience flying a major cross-country
without full use of a nav/com radio you are in for a joyous learning
experience. I flew to Quebec from California with a radio that
only allowed occasional use of radar facilities. I flew from Seattle
to the S.F. Bay area with only a com and no nav. all of this was
pre-GPS. I have been below nav/com reception altitudes in the
Nevada deserts and saved myself by having a GPS.
I was much happier flying without the GPS because I was using
pilotage and always knew where I was by reference to
landmarks and the charts. With the GPS I was wandering unfamiliar
terrain where nothing on the chart could be identified. Surrounded
by weather and featureless terrain. Couldn't go IFR because of
any communications. I am very much against
being so dependent on GPS. A major navigational concern in instruction
is the tendency to drop all alternate forms of
navigation and use the GPS. In the future we can expect to see
accidents caused by use and misuse of the GPS.
The LOng RAnge Navigation system was developed during WWII by the Navy for ships. Because of vacuum tube size and power requirements ship LORAN was too large for aircraft. By 1943 an airborne LORAN the APN-4 was small enough to be used on large bombers and patrol aircraft. The APN-4 consisted of two units each about 1' x 2' by 2.5'. One unit was the power supply while the other contained the oscilloscope display tube and timing circuits and receiver. Together they weighed about 80 pounds. By 1945 the APN-9 came into use weighing 40 pounds.
The oscilloscope screen was about four inches in diameter and
would display a station master and associated slave signal from
about 1500 miles over water and 600 miles over land. Once the
two signals were received and aligned a timing circuit could be
displayed to measure the microsecond difference between reception
of the two signals. A LORAN chart of the area had numbered parabolic
lines which mapped out the lines of position for each time difference
between the two stations.
Once this was done the process had to be repeated using another
pair of master/slave station signals. The Chart had different
colored parabolas for each pair of stations. With practice a fix
could be determined in about three minutes. The minimum error
for navigating the 1400 miles to Japan from Tinian was about 28
miles. With two successive fixes ground speed, drift, and ETA
could be determined. As more islands were made available a third
pair of stations could be added to improve fix accuracy. The relative
simplicity of LORAN and the fact that it could be used regardless
of weather made it invaluable until landfall on Japan enabled
airborne radar to make a better fix. Fuel savings made possible
by LORAN probably saved more lives than did the capture of Iwo
Jima.
For some unknown reason the Japanese either never tried or failed to jam any of the LORAN systems. Loran - A as this WWII system was called existed worldwide up until 1985. The military sets were over APN-35 and had been reduced in size to less than a shoe box and had completely automated locating the fix while including ground speed, distance traveled, distance remaining, and ETA.
In the late 1980s LORAN - A was being replaced by LORAN - C. Loran - C used a chain of stations and a Loran receiver that programmed the station components of the chain so that multiple LOPs (lines of position could be simultaneously received and translated into longitude and latitude coordinates. Loran -C can compute from your departure point or your present position to a destination a direct bearing, distance, ground speed, and ETA.
The low frequency of Loran removes the VOR line-of-sight problem. 23 stations give an average accuracy of less than 1/8-mile cover the entire U.S. There are limitations depending on the database used. If your database does not have terrain elevations, Loran can fly you a direct route from CCR to Merced via Mt. Diablo. Class C and B airspace may not be included or kept up to date. Your Loran may die of a voltage spike to its power transistor. Use it and trust its accuracy but don't depend on its ability to always be available. Pilotage is the only navigational system that doesn't quit until you do.
On the West Coast we have the 9940 chain. The master is at Fallon Nevada with three slaves stations at George (Central Washington State), Searchlight (Death Valley, and Middleton ( Between Calestoga and Clear Lake). The 9940 designation has to do with the total number of microseconds (99400)it takes for a cycle of signals to go between the stations. At 99400 microseconds the data of the Loran receiver clock is updated about 15 times a second. Your Loran receiver uses the time difference of the signals received from the master and each of the three slaves to get three simultaneous LOPs (Lines of position). As you fly beyond one chain you are going to be in range of another. Just how the change will be made, manual or automatic, depends on the sophistication of your Loran.
One of the displays on the Loran is a Course Deviation Indicator or CDI. More expensive displays may have a moving map indicator. These displays will indicate which direction and how far off the straight-line course original selected you have flown. Some displays will give you headings required to establish yourself back on course. Some databases have about 30,000 waypoints so that you do not need to enter in longitude and latitude. Longitude and latitude does work. Over ten years ago I figured the longitude and latitude of Medford, Oregon and put it into a Loran when leaving Nut Tree. It read 1/2 mile when we were on short final.
Loran - C is operated by the Coast Guard at a price of $25 million a year. With the advent of GPS it is not long for this world except that it is a more viable and inexpensive system than the VOR..
How do I know all this? I taught LORAN-A in India and on Tinian to replacement crews as they arrived from the States. I was assigned to the Wing Training School of the 58th Bomb Wing of the 20th Air Force. (B-29s)
The HSI or Horizontal Situation indicator is a refined VOR/ILS
indicator with a directional gyro plus heading bug. In unison
they provide the pilot with a heading/course reference, course
deviation and glideslope.
The HSI makes it easy to determine via the split needle the difference
between your selected course and the deviation from that course.
There is no reverse sensing even on backcourse approaches. The
markings on the heading indicator have very handy 45 degree; markings
for use in heading intercepts and best of all a heading bug.Only
when the aircraft is on the selected radial will the course deviation
bar been centered. The station pointer always points to the VOR.
There are both vacuum and electrically powered HSIs (Horizontal Situation Indicator}. Check to be sure which you are flying with. The vacuum pump has the highest failure rate per hour of operation of all instruments used in IFR. Fly with a pack of post-its sufficient to cover all instruments of doubtful reliability. The vast majority of uncontrolled IFR flight begins with a loss of roll control. Attitude indicators tend to fail first in pitch.
Weather
use of ADF
1. Tune into the 400 kHz frequency range.
2. Avoid any signal reception of a station
3. Needle should rotate at random
4. Turn up volume control to hear static
5. When you hear loud static crash note needle direction
6. Needle will point toward lighting strike
7. The quickness and directness of needle can be used to determine
distance.
Navaid
Unmonitored
Navaids associated with a particular ATC facility have failure
or fail-safe devices that warn of failure. These warnings are
not available when the facility closes. Even with the facility
open the failure may not be noted, or if noted not passed on to
an aircraft in the vicinity. The best advice is to always identify
the code of the navaid and keep the volume so as to heard should
it suddenly stop. Prior to flight always check NOTAMS to confirm
operation during the period you expect to be using the navaid.
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