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Electronic Navigation
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Electronic Navigation History ; Very-high Frequency Omni-range (VOR); ...VOR Procedures; …Reverse Sensing; …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); ...How GPS Works; ...Selection of a GPS; ...Charts and Data Bases; ...About the Garmin GNS 430.530; ...   GPS Procedure; ...GPS and Situational Awareness; ...The Negative Side of GPS; ...LORAN; ...HSI; …Weather Use of ADF; …Navaid Unmonitored; ..Instructors Only: …The Disappearing VOR; ….VOR Exercises; …Opinion; …VOR Checks; ...What is the 1:60 Rule:  …Revisiting the ADF; …ADS-B ; …Garmin GPS; …Garmin 295 VNAV; …Garmin GPS Technology; …Learning Flight Management Systems; ...Course Reversals; …GPS Items; ...Direction vs Altitude; ...A Better Way to Fold a Chart; …GPS Emergency DataThe VOR the Way It Was Meant to Be;...Garmin 430;  ...About the TACAN VOR; ...Garmin Does Me Right; ...Garmin PDA Hits Market; ...Glossary; ...On GPS and Vectors; ...GPS Updates as Preventative Maintenance; ...

Navigation History
I fought the celestial vs electronics battle through most of WWII. I was with the B-29s initially in India as radar bombardment mechanic. I had learned LORAN at Boca Raton, FL and it became my duty to try to keep the APN-4 in my group (468th) operational. The set was in two units each the size of a 19" TV. 80 vacuum tubes made it operate until higher altitudes caused electrical malfunctions. Only good for 600 miles at night in the best of conditions. Reliability always in doubt due to tube failure, vibration of connections, corrosion and operator skills..

The Identification Friend or Foe (IFF) of WWII had eight codes in a 10"x 10"x 10" case which also included a thermite inertial bomb to destroy the interior on crash impact. British code name was "Parrot" which is why we still squawk. We now have our transponder soon to be all Mode S to tie in with the Automatic Dependent Surveillance
-Broadcast (ADS-B) and Traffic Information Service-Broadcast (TIS-B) which will give you all the information that ATC now has and spells the doom to RADAR as we now know and use it.

By ship to Tinian in the Pacific. Assigned to 58th Wing Training center to teach LORAN. New B-29s coming over with APN-9 which was only the size of one 19' TV and ‘only’ 40 tubes.. New planes were taken over by senior officers and older planes assigned to new arrivals. Result was that I was given the job of training old navigators on the -9 and the new on the -4. As a Corporal instructor I ranked my students none of whom wanted to learn about something they had previously learned not to trust. Tough teaching assignment but made me want to become a teacher.

Much of the 1400 mile flight to Japan was at lower levels with stations on islands like Ulithi. Good LORAN range and accuracy. Flights required passage through weather fronts that reduced use of celestial navigation and increased reliance on electronic. We even had first inertial systems which read out longitude and latitude as an odometer in the newer planes.. My plane has a hard-wired LORAN the size of cigar box. Last military LORANs were in the APN-30s.  Still celestial ruled with electronics a step-child category.

As an instructor on the very newest of electronics I was seeing the birth of DME as the slant range to a bomb release point. RNAV as used to put bearing and distance to radar visible target to hit non-radar target. Even the first German radio controlled bomb was instrumental in sending me to India as a replacement....

At war's end, I was operator/mechanic of a supersonic bombardment simulator that had the Nagasaki Chart installed for practice radar bombing runs in the immediate vicinity of Nagasaki.  (Look at end of IFR for more 7.91 through 7.94)  Device used tank of water with underwater glass maps made of sand and beads to give radar-scope pictures of Japan by using a vibrating underwater crystal to send to-scale transmissions and echoes back to the scope.

At the time it was so secret that I had no idea that I was at the cutting edge of electronic development that with education and time could have been a most rewarding career had I been allowed to know.

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.

The term 'reverse sensing' comes from operational problems using the VOR TO/FROM window and the |
OBS radial selected. In general you are either going TO or FROM a VOR radial. The instructional rule of
thumb is to always fly toward the needle.

If you are going TO the VOR radial and the window shows TO you always fly toward the needle when it is not centered as the process for centering the needle.

If you are going FROM the VOR radial and the window shows FROM you always fly toward the needle when it is not centered as the process for centering the needle.

Reverse Sensing
In general you are either going TO or FROM a VOR radial.

If you are going TO the VOR radial and the window shows TO you always fly toward the needle when it is not centered as the process for centering the needle.

If you are going FROM the VOR radial and the window shows FROM you always fly toward the needle when it is not centered as the process for centering the needle.

If you are going TO the VOR radial and the window shows FROM any flying toward the needle will make the needle move even further away from center.

If you are going FROM the VOR radial and the window shows TO any flying toward the needle will make the needle move even further from center.

In the REVERSE SENSING the foregoing rule of thumb will not work because the needle sense of movement is backwards..

The term 'reverse sensing' comes from operational problems using the VOR TO/FROM window and the OBS radial selected..

If you are going TO the VOR radial and the window shows FROM any flying toward the needle will make the needle move even further away from center.

If you are going FROM the VOR radial and the window shows TO any flying toward the needle will make the needle move even further from center.

In five years (2010), with the removal of VORs, the whole problem is moot.

VOR Procedures:
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.

Revisiting the VOR
--First confirm your frequency and ident.
--Make your from or through decision. Never fly TO a VOR always fly through it.
--Confirm to or through by reference to heading indicator and compass. This prevents reverse sensing.
--Reverse sensing is most disorienting when location of VOR is unknown.
--Any difference between the heading of the aircraft and the VOR radial will be a wind correction angle.

VOR Lesson
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.

VOR Lesson Diagrams
North, centered needle, Reverse sensing, side, Region of ambiguity, Region of flag reversal, VOR flag reversal ,

#1 360's on 135 radial

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

Flying From a VOR to Intercept a Radial
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

Finding Position by VOR Radials
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.

Procedure (time to station)
1. No wind conditions
2. Established needle centered on radial and turn 90-degrees.
3. Center needle again and start timer. Assume 090 from
4. Set OBS ahead of flight direction by 10-degrees. 090 + 10 = 100 as new OBS setting
5. When needle centers stop timer. Assume 150 seconds elapsed time.
6. Drop the 0 and you get 15. It will take you 15 minutes to fly to the VOR.

This is a good exercise to practice at night with a FSS. This is so seldom done that you might call before flying to advise them of what you want to do. They are still required to maintain their proficiency in doing this. The specialist I just spoke to had not had a pilot ask for one in nine years.

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

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.

Distance Measuring Equipment
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

Poor Man's DME
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.

VOR Disorientation Lesson
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.

Using Global Position System (GPS)
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 measures 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 up-gradable 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.

How GPS Works
Every type and model works differently using selected operating conventions. The U.S. Military launched the first of 24 satellites in 1978 and set up ground stations to keep the system working. It was called the Defense Navigation Satellite System.

The Global Positioning System or GPS as it is now called works much as a three legged milk stool, triangulation lathe GPS receiver needs to select three satellites to locate a specific point on the ground or in space. It uses a fourth satellite with an atomic clock system to verify the accuracy of the other three satellites. The radio signal of the satellites is broadcast and received on 1575.42 MHz.

Every one of the satellites has a discrete identification code known as a PRC. Before your GPS receiver can verify its position, it must find a correction factor for all four of the satellites meet at one point. An aircraft GPS should have at least five satellite capability Twelve is now the aviation standard. As the satellites circle the earth in their orbits slight variations of position occur due to other gravitational forces in space. Ground stations are constantly making corrections in the satellite clocks relative to their position at any given moment. Atmospheric differences and reflections can vary a signal but most receivers can adjust to these problems.
GPS receiver come in three forms sequential, multiplex and continuous. Continuous receivers are used in aviation and use a minimum of five satellites and have accuracy within several meters. More accurate GPSs are valid within centimeters.

Tests and/or usage of ground-based jamming equipment. are used often as well as uploads of data to check operation, security and reliability.

Each satellites is checked at least once a day but still provide uninterrupted service. It is not really possible to deny service to specific geographic areas by switching off satellites.

Free how-GPSs-work program available:
Garmin also offers a lesson plans/flight syllabus document for the GNS430:

Selection of a GPS
--Moving map
--Zoom capability
--Different views to be selected.
--Nearest function
--Go to function
--Flight planning function
--WAAS capability
--Substantial database
--Updated data base ($600 per year)

Charts and Data Bases
--Lack of memory makes it so that many systems do not have all holding patterns or only right turns shown.
--Databases are not intended as substitute for charts.
--Databases will contain TF (between two fixes) legs. The path charted may extend beyond the last fix.
--The database may not include "fly-over waypoints' since by definition all are fly-by waypoints.
--Phase two approaches of 1992 requires GPS approaches be monitored by the underlying paper chart. (obsolete)
--Phase three overlays allows an approach to be flown without chart monitoring by navaid. Chart says "or GPS.
--The new RNAV (GPS) will do away with the GPS and the overlay procedures.
--FMS (flight management systems) and GPS approaches must have an initial approach fix for their database.
--Some approaches are so complex that they exceed the database capacity to program.
--Charts are needed for all FMS and GPS approaches

About the Garmin GNS 430/530
--430 has 1.8 by 3.3 inch screen at 128 x 240 pixels; 530 has 3 by 4 inch screen at 234 x 320 pixels.
--Both have a12-cheannel GPS, a 760 flip-flop com at 8.33 kHz split and a complete VOR/LOC.
--430 has one nav page while 530 has two. Total customizing exists except for location on nav/com windows.
--The database has full info about every airport, waypoint, route, navaid, airspace, chart and sectional
--Digital display gives radial direction, distance, waypoint, track, desired track, distance and ground speed.
--Cursor and scrolling can highlight and get info of any detail.
--Default nav page is north-up map display with course line and waypoints shown.
--Aircraft and weather is there for a price.
--IFR capable GPS uses ground stations for increased accuracy. Improvement applies to altitude, too.
--The 295 has WAAS capability
--Flight plan key gives both building or activation of plans.
--Waypoints or changes can be made using delete or insert buttons.
--Dedicated procedure key lets you select airport and approach procedure IAF and vectors are options.
--Software plans appropriately as it determines your current position and gives the full procedure with missed.
--Timer appears appropriately for timing legs or approaches.
--All approaches are setup and displayed the same way, the pilot must perform the descent.
--Required approach frequencies automatically appear on the standby window.
--The OBS button gives the missed approach procedure at the FAF.
--Climb and descent needed is displayed by pushing the VNAV button. Time to begin is displayed as well.
--"Nearest' display gives closest airport or navaid including frequencies and airspace.
--Put in the data and the system will keep track of your fuel situation.
--Any combination of two Garmin can intercommunicate and share information.
--Multiple timers and trip statistics, altitudes, overlay of lightning data is there at a price.
--Annual data base costs $650, list for 430 is $9250, for 530 is $14,995

GPS Procedure
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

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.

--GPS-oriented pilot is likely to focus too much on the moving map close in presentation and lose the situational awareness making the big picture.
--DTK (desired track) is only wanted when you are established on course. Better to use BRG (bearing)
--You must adjust for wind correction to make BRG and TRK agree.
--Choose XTK (cross track error) instead of TKE (track angle error) or CTS (course to steer)
--Always include DIS (distance) and GS (ground speed)
--Use map display when possible. CDI is five-mile range. 10-mile range is good option.
--IFR GPS can substitute for DME if with current database. Use 'along track distance' from FAF in CDI mode.
--When changing letters count clicks alphabetically instead of staring. Limit your 'eyes down' time.
--Non-GPS approaches are not in database. Use localizer and OBS mode with FAF as waypoint.
--NRST and D gives you stepdown points.
--DME location may not be in database. Suggest always using FAF write numbers on chart.
--When on ground buildings may affect signals.
--Susceptible to atmospheric effects.
--Signal may be affected by communications frequencies.
--Signal may be deliberately degraded by operator of system.

The Negative Side of GPS
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.

According to an article in the November 2004 edition of Scientific American, the GPS satellites' clocks have a 7 microsec per day effect due to relativistic motion and a 45 microsec per day effect due to the lower gravity in orbit. The two effects partially cancel, so the net adjustment is 38 microseconds.

Item: (Opinion)
I attach my Magellan Tracker ($150 at Kmart 2 1/2 years ago) to it, along with software from, and it works as well and is as fuctional as any $1500 aviation GPS I've seen.

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 glide slope.
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 back course 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.

Instructors only,
I have posted this before but a couple of weeks ago I had a student from many years ago become the first pilot to escape my instructor 'trap'. During the process of taking a pilot through a series of unusual attitudes, I will reach over and take a substantial change in the heading indicator setting. I do this when the pilot is unable to see what I do.

After the unusual attitudes have been completed, I give the pilot a VOR frequency to a seldom used VOR and direct him to fly us to it. Unless the pilot is really on top of use of his checklist, he will neglect checking the compass/HI setting. The resulting effort to fly to the VOR can be very disorienting. Enjoy.

The Disappearing VOR
The VOR is not long for this world. As long as it exists we should learn to use, interpret and fly it with
understanding. More importantly we need an awareness of how it can be a mind confuser.

Try the following exercise:
Locate a VOR in Class E airspace. Fly about a long mile to the southeast side of the VOR and set the OBS on 360. The lower you fly the better (less traffic).

Turn to a North heading and fly until you are approximately northeast. Do not make any changes in the OBS.Next fly due West until northwest of the VOR, then South until Southwest and then East until you are southeast. Watch the needle and the to/from carefully.

You will have flown a cardinal heading 'wrecked tangle' or square about a mile out from a VOR. You should be able to see the deviousness of the VOR needle and the to/from flag.

Reverse the direction of flight about the VOR and fly it still leaving the OBS on 360. Now comes the more interesting part. Begin to predict at which point the needle will center and to which side it will swing. Make an effort to predict the changes in the to/from window. Enjoy!

VOR Exercises
I have an exercise that I use to help students understand the way a VOR works and why 'reading' the course deviation needle can be confusing.

Set the OBS to 360 and fly a square around a VOR within a mile beginning at the southeast corner. Leave the OBS alone and watch the way the needle and TO/FROM/ OFF readings change. Second time go around in the reverse direction and see how well you can predict the readings before they occur.

For over the VOR work I use two-minute legs tracking into/away from the wind followed by a course reversal and back again. Second series does the same but across the wind direction. Good initial IFR exercise.
My aircraft has a DVOR which gives a digital readout of VOR radials. Jerry K told me that I would learn to like it and he was right.

I fly down the one airway with the second VOR tuned into the station with the intersecting radial/airway. I set the OBS for the radial, or outbound heading/course of the intersecting radial/airway. When the needle is centered, I'm there. Bout the only simpler is GPS.

I had one instructor fail all the radios except the #2 VOR (the one without DME). He then put me on partial panel. I had to intercept an airway, fly to an intersection, do a hold (all timed turns and legs) and then fly a complete approach from the hold. One radio, no DG, No AI, just a TC, altimeter, compass, ASI, and VSI. Good thing he didn't fail the clock and tach too. <:-)) I think there was a constant rate descent to the airway too.

VOR Checks
--FAR 91.171 requires IFR VOR checks to be made and certified within past 30 days.
--Though checks may be made, most frequent violation is failure to record and certify check
--Certification requires that VOR be within specified operational limits.
--VOR vs.VOR within 4-degrees.
--VOT test facility found in AF/D within 4 degrees as shown.
--Radiated VOT from radio repair station within 4 degrees.
--VOT check at FAA designated ground checkpoint within 4 degrees
--Airborne checkpoint from AF/D within 4 degrees
--Created airborne checkpoint using airway and checkpoint within 20 miles of VOR. 6 degrees.
--Recorded entry must be dated, signed, as to time, date, place and bearing error to/from.
--Retain record at least until flight completed.

What is the 1:60 rule
If you are flying perpendicular to a VOR radial, every degree of bearing change is worth 1/60 of the distance to the VOR. It's a handy estimation rule.

So, in the case of the approach you cited, the FAF is 17.6 (round it off to 18) miles from the station. So, each degree is worth 18/60 miles. 4 degress is worth 4*18/60 or 18/15 or about 1.2 miles.

If you took high-school geometry, you might remember three ideas:
1) Arc length is included angle times radius, s = r*theta, with theta in radians.

2) 1 radian is 57.mumble degrees, which you can round off to 60.

3) For small angles, you can approximate chord length = arc length.

Put those three together, and you have the 1:60 rule.

I suspect it's a dead art, but when I was in engineering school, we were taught how to approximate ruthlessly. If you're trying to aim a rocket so 3 years from now it's in the right place to do a slingshot maneuver around Jupiter, you need to crunch a bunch of decimal places. For most other things, being able to get in the ballpark without reaching for calculator, pencil, or paper, is very handy.
Roy Smith

Revisiting the ADF
--Simplest of electronic navigational systems. Fly to the needle to get there.
--Correcting for wind requires flying with needle not centered on ADF
--You have corrected for wind if needle remains fixed.
--Use ADF to give location of compass locator (outer marker) on ILS approaches.

ADS-B (automatic dependent surveillance-broadband)
--Aircraft altitude and position sent to satellite for re-transmission.
--Cockpit displays share information between ATC and aircraft
--Information is distributed and is redundant over the whole system.
--Includes moving map airport diagrams.
--Allows GPS aircraft to tell of its position to ATC and other aircraft.
--ADS-B will work on the ground and at airports as well.
--ADS-B can provide collision avoidance information.
--ADS-B will allow free-flight and direct to destination.
--Part of the ADS-B display is a vector arrow for each aircraft related to direction and speed.
--ADS-B is an add-on to existing equipment at a price below $1,500.
--Question: Why the governmental delay????

ADS-B (automatic dependent surveillance-broadcast) 
Has been under development for a decade or so, and its deployment in Alaska has been credited with helping to improve the safety statistics there.  Now the FAA has announced that it's available on the east coast, in a developmental phase.

The system provides equipped aircraft with traffic advisories even in areas that are out of radar range, and also brings terrain information and real-time weather to the GA cockpit equipped with a multifunction display.  It allows both controllers and pilots to see equipped traffic during ground movements, 
and helps pilots to find their way even on strange airports.  The system can display airspace restrictions as well. Access to the weather and traffic information is free. 

Garmin GPS
Capable of being programmed one time to do all the VNAV you need. Preset it to arrive at pattern altitude a selected distance from the destination. Select the rate of descent per minute you prefer. GPS will advise when it is time to start down. Push the VNAV key and it will tell you the rate of descent you will need. Once you are at the proper rate of descent push the VNAV key again and the regular screen will appear.

GPS Items
--A single source IFR device by using the flight plan and procedures buttons.
--Flight plan button will activate at any time.
--Multiple Garmins will interact so that what you do to one also happens to the other.
--If ATC throws you a route change push the flight plan button and go to the next cleared to point.
--The Garmin can be a virtual ILS, VOR, or NDB just by pushing the OBS button.
--Procedure button before departure gives airport leaving, afterwards it is the arrival airport.
--You can ignore GPS caution to use actual instruments. Fly the approaches on the GPS.
--Transfer button will flip frequencies.
--Localizer course may be magenta. Actual localizer moves much more than virtual GPS localizer.
--GPS and VOR approaches are usually overlaid. GPS is easier to fly.
--You are following your course when GPS track and desired track are the same.
--Having two Garmins is the best of all worlds.
--Short cut IFR, like turning inside the FAF, is difficult to fly using the GPS because it is out of sequence.
--Has a scheduler that allows setting point of required inspections, oil changes, etc.
--Time is counted as flight time when above 30 knots.
--Hobbs time is engine running time which is the time Garmin uses. Not time for maintenance work.
--Always have twice as many batteries as you need.
--Always verify GPS by using sectional and looking out the windows
--GPS has removed the fear of getting lost
--RNAV (GPS) is chart type now within thirty miles of the airport.
--GPS approach mode is most sensitive setting
--GPS does not allow (will not recognize) short cuts.
--Finals will be aligned with runways.
--RPN on chart indicates Required Navigational Performance for oceanic, enroute, terminal or approach.
--RPM 0.3 means that your navigational system must keep you within .3 miles of course.
--Initial segment obstacle clearance is 1000', intermediate its 500' and final segment is 250'
--RNAV approaches are T shaped area called TAA or terminal Arrival Area.
--Approach is ten-miles long with a ten mile IAF and a five mile FAF and two arms of three mile waypoints
--Way points are either fly-by which have a leading turn or fly-over such as the missed approach point
-- Local Area Augmentation System (LAAS) is expected to replace the ILS
--Wide Area Augmentation System (WAAS) is waiting in the wings.
--Don't use GPS for precision approach unless required data is in the bank.
--GPS VFR database is not legal but adequate for doing DME arcs.
--GPS only knows track. Track is not where the nose of the aircraft may be pointing. Look to the downwind side of the nose to find your destination.
--You can program the GPS to arrive from any direction you wish. By selecting runway heading the GPS uses the center of the airport but it may not be aligned with the runway in use.
--The arrival is planned before takeoff and finished en route.
--Pure GPS approaches are either the Basic T or a Modified T
--Basic T is + shaped with extended lower leg. The arms are IAFs the intersection has a hold and the long arm has three intersections at 5 miles and three miles (variable) and threshold fix
--Questions can be answered as yes with ENTER or no with CLEAR
--There are three modes of sensitivity, en route, terminal, and approach
--Approach mode is 16 times more sensitive than en route mode.
--Common error is failure to do approach in the approach mode.
--Always start GPS by initializing position.
--Activation always requires two clicks for approach
--Hold CLEAR for three seconds to return to primary (first) page.
--Turn off cursor before using any 'lost' procedures
-- To delete an approach and put in a new one all that is needed is to put the cursor over the title of the approach
and clear it out and then click on the new approach you want.

Garmin 295 VNAV

How can I use the VNAV feature?
You need to enter the descent profile that you'd like to use on the main set-up menu (MENU-MENU scroll to VNAV). Without it, you'll get unexpected results. You need a 3-D fix in order for VNAV to work, 4 or more satellites will do. Also, make sure that the target altitudes are set for each waypoint enroute. If you use an aerodrome for a WP you might have funny behavior if you don't plan to land there... Use a UDWP and set a cruise or fly-over altitude for that point.

I called Garmin and received a few responses. They suggested that I update the firmware to the latest version AND then do a hard, cold reset of the unit. This will erase your USER waypoints, but it DID eliminate the reset problems. The reset instructions from Garmin are included below:

There is master reset sequence you can perform to your unit that should fix this problem. Please note that this will erase all personal waypoints you have stored. It will not erase your aviation database. You can reset your unit as follows:
WARNING: The following reset will delete all user data, including all routes and waypoints.
1. Turn off the unit.
2. Hold down the ROUTE and QUIT key while you turn on the unit. There should be a 2-second delay.
This is a hard master clear and hopefully you will not need to send your unit in for repair. Also you are correct in the assumption that WAAS may contribute to this problem. We may be coming out with v2.22.

Garmin GPS Technology
--With two GPSs set one for the departure and the other for returning to airport
--With two GPSs set one for the VOR course and the other for the intersecting VOr radial.
--For arrivals and departures set both to the same situation as a cover if one fails.
--En route have one as a map display and the other as the trip information page
--Approach option is have the map on one and the missed on the other.
--Set 'crossfill to automatic in one and manual for number 2 makes sharing of information easier.
--Use number one for communications and number two for recorded information and 121.5
--Use nav pages in number one for closest VOR and Use menue to change field to VOR and FROM for position.
--On number two nav moving map always used North UP mode.
--Use instrument CDI and HIS for course instead of GPS because scale changes are deceptive.
--Set number two to show all airports within 100 nautical miles.
--Insure automatic scale from enroute to terminal by using flight plan page
--Use TRK and DTK on number two for interception of localizers to help use of CDIs.
--When all else fails hold the CLEAR button until you get NAV one screen.
--System operated through use of menus, submenus, buttons and switches each with multiple functions.
--Exterior scan is greatly decreased with use of GPS.
--Direct is always possible by placing cursor on point and hitting direct twice.
--Non-procedure landings with self made localizer
--Make a runway extension with VNAV reference point one mile from end of runway.
--Name the waypoint and press direct will make it the active waypoint.
--Moving the cursor to your present position and ENT twice

Learning Flight Management Systems
The multifunction display and the nav/comms are connected to the GPS moving map for downloading of active frequencies and flight plan information from the data base. It will take about 3 days to learn the procedures, about 1 day learning the programming, and a few hours to learn the interrelationships which have up to six different display modes. Regardless of your background do not underestimate the learning time required for basic operations. Mastery takes much longer than one would think.

The FAA's inherent lethargy was unable to act as new avionics systems among the manufacturers came into being. Because of this there is no uniformity as to controls, logic, display, layout and operation. Only the operating requirements and installation certification are standardized.

A pilot intending to use a flight management system must become a systems manager. Other than adding power for takeoff and reducing power for landing the aircraft is controlled and directed by the autopilot. The remainder of the flight is spent updating changes and programming the flight management system. It is the unexpected results from programming mistakes or data glitches that require constant pilot attention and awareness to the flight being flown. Flight management systems can pre-select, climb/descent rate and altitude, go-arounds and when linked to VNAV the autopilot can fly the airplane all the way up and down as well.

Collision and thunderstorm systems are linked to real-time uplinked weather data. The complexity of the flight management systems has outgrown the training programs available. Small aircraft are unique in their avionics installations always in the search for safety and economy. The downside is that the pilot must sort out, process and evaluate more information than he has been trained to expect.

Every applicant for a certificate or rating is expected to know how to use any systems in the aircraft used for the test. A pilot must seek out what training is needed and how to get the training specific to the systems installed. You need to learn what you need to know, you need to go to where the teaching exists for the learning required and you must progress through the plateaus of training to gather the background required to eventually become master of the flight management system. The actual flying of the aircraft is incidental. An instrument rating practical test passed in a Cessna 172 with minimum avionics can fly in a complex flight director equipped aircraft. The issue is whether he can manage such an aircraft with a flight director/autopilot system and approach-certified GPS, and use it to fly a coupled GPS overlay of an NDB approach using the ADF as a backup/monitor.

Each piece must be studied as to how it works by itself and then how it is integrated into your flying of the aircraft and with the remaining pieces of the total flight management system. Need to know information is recognition of the various failure modes and how to resume hand flight as required. A preliminary thorough reading of the unit-specific documentation is just a start. Go to a PC-based simulator that you can download free from a manufacturer's web site would be the next step. Be aware that the information from the autopilot manuals is not as good as is that available for electronic systems.

The Aircraft Flight Manual Supplement exists for every flight management installation. The FAA requires avionics shops to put together an individualized manual that lays out the linkages between parts. This will identify what to do to accomplish a specific task or series of tasks such as getting the autopilot to track the ILS. It will also specify which options are both installed and operational. The supplied manual is all you are going to get to learn how to use the system from the manufacturer and installer. You would be well advised to get some expert tutoring after you have become reasonably acquainted with the systems. Truly qualified instructors are difficult to find. There are training organizations available at a price.

You may need to teach yourself. Use a step by step approach by learning one process at a time. Make your own checklists and how-to cheat-sheets. Learn one operation at a time. Once you can do all the individual operations you can begin to integrate the operations while making your own specific to aircraft operational manual.

Knowing when to say when, and how to say when, may be the most important thing you have to learn before using new equipment, especially autopilots. Do all your flying in VFR our under the hood in VFR until you fully understand the programming process and the operational process. Make sure that you know how to shut down everything and fly using traditional instruments. When going IFR practice using the traditional systems with the flight data system as a backup. The flight data system will fly the same routes and procedures that you have set up into your traditional system so that in a two pilot situation one will always be available as a backup.
GARMIN International
1200 E. 151st Street
Olathe, KS 66062 USA

Course Reversal
The distinction between a direction reversal and a course reversal has to do with the original 'line'. A direction change like a left/right 180 moves you off the original line. A course reversal can be accomplished by the 45 to one side and a turn in the opposite direction at a specific point. The problem is finding the point.

The holding pattern is often used as a course reversal based upon a specific airway point from which the racetrack pattern is entered by way of a teardrop entry either left or right. On arrival at the course intersection the initial turn is 30 degrees to the side and after two-minutes a turn is made back to intercept the original course line but on the reciprocal course.

In the recent past, the FAA via the AIM has relaxed the requirement for use of the teardrop entry and now accepts the use of a course reversal using the 80/260 method. I very much prefer using the 90/270 method which works just as well and requires far less mental gymnastics.

To illustrate my point I will walk you through the 90/270 process. Using the headings of 360, 090, 180 and 270 all of which are in the form of a +. The seldom noticed fact is that they all add to nine. All numbers of the compass rose that are in the shape of a + one from the other. Check this out beginning with 020, 030, 040, etc. Knowing this 'sum of the digits' pattern can be quite useful in making turns of multiples of 90-degrees or 45-degrees with a manual E6-B or an ADF card.

On an initial course of 360 (3+6+0=9)we want to reverse that course. We look at the heading indicator and find that the reverse course is 180 (1+8+0=9) A teardrop hold will be either to the left or right side. To the right the 90-degree number is 090 (0+9+0=9);to the left the 90-degree number is 270 (2+7+0=9. Prior to making any course reversal you look at the heading indicator and select first the number for your initial 90-degree turn. The subsequent number at the end of the 270-degree turn is at the bottom of the heading indicator. On completion of the left/right 270, 180 will be on your nose.

A basic VOR training exercise that I use is to determine the wind direction over a VOR, I then turn the whole world until the wind is from the North. (That's an airplane joke, son.) We cross the VOR directly into the wind and at the end of two minutes initiate a 90-270 course reversal back through the VOR for two minutes to perform a second 90-270. All banks are at the same angle. I usually use 30-degree VFR bank angles. These reversals tend to be 'perfect' because we have removed wind correction as a problem. The next part of the lesson is to do the same process crosswind and adjusting the 270 turn to intercept the desired course.

I also teach the course reversal as a part of the overfly and pattern entry into uncontrolled airport patterns. After we have determined the active runway by reading the windsock, we fly an outbound 45-degree course from the runway heading and descend toward pattern altitude. While doing this we use the numbers on the heading indicator to select the 90-270 numbers we will use for our inbound 45. Winds will always have some effect but this is as good as it gets at unfamiliar uncontrolled airports. The entire process is very much easier if you have a heading bug and set it to the landing runway heading.

GPS Items
95-percent probability of accuracy within 100 meters
--99.99-percent of accuracy within 300 meters.
--The signal of the GPS is called the course/acquisition code
--The satellites used by the GPS have a position known as ephemeris
--The internal computer logic of the GPS used to determine accuracy is RAIM (Receiver Autonomous Integrity Monitoring)
--The standard GPS FAF waypoint is five miles from the threshold. (It can be any distance)
--The approach mode of a GPS will automatically be 'armed' at two miles. (It can be more or less)
--The minimum safe altitude circle for a GPS can be centered on any available navaid.
--The waypoint for a GPS approach missed is at the runway threshold.
--GPS straight-in minimums are published when within 15-degrees of the runway centerline.
--GPS approaches are T shaped with the crossbar having three IAFs the middle may require a hold.
--Do not try to program a flight while dealing with ATC.
--Program an alternate fight plan along airways or based on past experience.
--Once you're cruising, figure the immediate and distant anticipations you expect.
--The events and timing to be considered in both short and long view are weather, routes and arrival
--Think ahead of the things that can go wrong and what it takes for you to make them right.
--Set Vnav function for desired rate of descent from a given point and the point where you want to reach a certain altitude and you will get a running number of rate of descent required.
---A Fix in the GPS that is not charted is a Computer Navigation Fix. It's a fix that's in your GPS's database, and marked on your charts, but ATC doesn't know about them. May appear on the en-routes and on approach plates. 

Direction vs Altitude
I fly out of Concord, CA. Within eight miles of the airport and eleven miles of the CCR VOR there is a single mountain called Mt. Diablo rising to 3800'. The AFD for that VOR specifies an a partial arc area of about 60-degrees to the southeast from which pilots are advised not to use the CCR VOR. The problem is that the so called line of sight limitation regarding the use of a VOR can cause accidents. MY usual
exercise to demonstrate this to my students is to take them to Livermore and then depart direct to CCR at about 2500 while under the hood.

I then tune in CCR VOR on 117.0 and center the needle and instruct them to keep the needle centered. Between ten and fifteen minutes later I have them take off the hood. Surprise, the VOR signal is strong enough to cause any aircraft using only the VOR signal to fly into the mountain.

There is a VOR near San Diego which is not on top of a mountain and it has led many aircraft astray and eaten a few as well. Loran and GPS has very deceptive negative potential whenever a pilot puts unwarranted faith in direction over altitude.

A Better Method for Folding Charts
You might want to try the following link.
It shows the method described below. First, unfold the chart and lay it flat. Now, fold the chart the long way. In other words, fold it so it is still 3+ feet long, but only 10 or so inches high. Still with me? Now, starting at the left side, fold the chart along the creases in alternating directions. So, make the first fold "over", the next fold "under", etc. If anyone is still with me, your should now be able to open your chart to any location the same as you would open a book. This is great for east/west flights. Like I said, it means you only get one side of the chart...but if you buy two copies of the chart, then you always have one ready to go for the side you are on. And it is SO much easier to keep track of in flight
.Kevin Thorley
Open an old sectional out until one flat sheet.
Suggest you run a sample marker line diagonally across the entire chart
Fold it into half lengthwise. Crease
Start at the left end and accordion fold all the way to the right side.
You can now use the folds like pages of a book to follow the line.
You never need more than two of the folds open at a time.
At the halfway point you flip the book over.
Try it, you'll like it.

To do a complete sectional you will need two of them. One for each side.

GPS Emergency Data
You need access to the correct information to help you in an emergency. You have a set of ‘tools’ available. The most important of which is the checklist. Using it to access all the other ‘tools’ that are emergency type specific is the best assurance that you will do the best possible procedure available.
--The GPS with vertical capability is a very nice tool to have available if a glide is required.
--One aspect of a properly applied GPS is knowing if you will reach a specific point from a specific altitude.
--Proportionately far two many engine-out emergencies result in accidents because of ‘fear of the g round’’.
--I recently took a pilot into a series of unfamiliar airports with short runways. He was high every time.
--If your descent required is more than your vertical speed, you will make the selected touchdown point.

The VOR the Way It Was Meant to Be
–This method will work only on VOR heads that have directional arrows for the to/from indication or if you know where the VOR is relative to your position.

--The VOR is the most misinterpreted navigation aid.
--The culprit is the variable possibility and probability of reverse sensing.
--The Omni Bearing Selector (OBS) consists of a dial of all 360 degrees of possible courses.
--If the OBS is set to the reciprocal course actually flown the standard of fly to the needle fails.
--The initial intent of the VOR design and system was to make it possible to fly a selected course.
--The needle of the VOR is called a course deviation indicator or CDI.
--The CDI will always point to the side of the desired course.
--The TO/FROM window point to the front or rear where the station is.
--You can intercept any radial course selected just by turning toward the needle.
--The quickest intercept is to turn 90-degrees to the course selected while flying toward the needle.
--Changing the 90-degree needle intercept to a 45-degree intercept front or rear toward the station.
--We can intersect from the station by making our 45-intercept away from the station.
--On intercept we turn to the selected course and make heading adjustments are required for wind.
--Reverse sensing is not a factor when using this VOR intercept method.
--Set in a radial from any other VOR that intercepts the course radial. The needle of the intersecting VOR will be towards the intersecting VOR and will move toward the center until reaching the intersecting point and then will move away from the station.
--If two VORs are so set that their OBS courses form an intersection but the CDI needles are pegged to the side. What to do?
--Look to the needle side of each VOR and select an OBS number that they have in common. Fly that heading.
--When one needle centers we are on one of the radials. Between the two possible directions to fly on that radial, chose the direction that is on the needle side of the VOR still to be intercepted.
--The beauty of this method is that you don’t really need to know where you are, just fly the procedure using appropriate headings you will soon know your position.
–A localizer frequency and needle is such that you set the course top center and fly accordingly.

Garmin 430
Challenge is to use to capability of the 430.
---Challenge is to limit heads-down time
---A pilot nav clearance is different than direct to
---Use GPS of Garmin to make runway extension for straight in arrival.
---Make it a localizer by making a way-point at one NM from threshold at 318 feet high.
---In Garmin you press enter twice to accept entry.
---Using the small and large knobs on Page 2 the cursor can be positioned and a way point made.
---Avionics Training Unlimited… training program

About the TACAN VOR
---The TACAN part of the VOR was mechanical many years ago that was nine times more accurate than the electronic civilian VOR signal and can be used aboard ships.
---The Ident pitch of the DME and VOR parts are slightly different pitch
---The military get both at once as a channel while civil aircraft can’t
---You can find TACAN frequencies in two ways
---For channels 17 to 59 add 63 put a 1 in front and a zero in back with a decimal point to give frequency
---For channels 70 to 120 add 53 put a 1 in front and a zero in back with a decimal point to give frequency
---Y Channels end in a 5 so add the 5 as well as the zero to make the frequeny end in .05
---Military information is available through the local base Public Affairs Office Flying Safety Officer.

Garmin Does Me Right
 On the Salem, OR Airport there is a Garmin facility that takes care of the Apollo 920 GPS series. I have had a 920 since 1993 that I used infrequently until I thought I had lost it. However, my wife found it where she had put it away while cleaning just last week. I contacted Garmin at the Salem airport and purchased a 2004 upgrade and cable for $158. I followed the instructions religiously. This involved deleting older data bases to free up memory. Well, I never got enough memory in the GPS or my head. I contacted Garmin and explained the problem. Seems my 920 was so old that I would never have enough memory. I essentially had killed my GPS. Apparently there was nothing to do about it so I gave up and hung up. 

In less that three minutes my phone rang. The Garmin representative said he had good news and bad news. I was prepared for the worst. The bad news came that I would have to pay to ship my 920 to Salem. The good news was that Garmin would upgrade the memory and install the latest database at no charge. I thought it was worthwhile for me to spread the good word to the group. In the near future I plan to upgrade my plane to an IFR GPS. Garmin it will be. 
Gene Whitt

Garmin PDA Hits Market
Here's a Palm Pilot worthy of its name. Garmin has married a moving-map GPS with a Palm PDA to come up with the iQue 3600A. The new device is based on a terrestrial version of the same concept (the iQue 3600) which combined all the organizational and entertainment capabilities of the Palm Pilot with maps, turn-by-turn directions and a geographical database to make it easier for business people, professionals or those hopelessly addicted to gadgets to find their way in the world. The aviation version adds a third dimension to the PDA's utility. The portable PDA snaps into a yoke-mounted cradle during flight. The cradle has the aviation-related buttons that identify it as a GPS. The Jeppesen database provides all the chart, physical and topographical information you'd expect plus a "TAWS-like" option that warns of potential conflicts. Snap the PDA out of the cradle and it's ready to record phone numbers or guide you to your hotel. Suggested retail is $1099. Similar non-certified products have long been available. Pocket PC-based MountainScope software, which can also work with programs that provide emergency backup for nine basic navigational instruments and devices, is just one example we've frequently seen at aviation trade

More Garmin
---Airspeed, heading and altitude in windows not dials
---Trends shown in magenta are airspeed, altitude and turn rate
---Garmin Rule of Six for smooth transition control
---Air Data Controller (ADC) makes Garmin function

Differential GPS (DGPS) — A method used to improve navigational accuracy by determining the positioning error at a known location and broadcasting a correction to receivers in the same geographic area.

Local Area Augmentation System (LAAS) — Provides signal suitable for precision approach for Category (CAT) II/III airports. LAAS also provides a signal suitable for CAT I precision approaches at airports where either WAAS does not provide adequate availability or where an airport is outside WAAS coverage.|

GLObal NAvigation Satellite System (GLONASS) — A Russian satellite-based radio navigation system which enables an unlimited number of users to use all-weather 3D positioning, velocity measuring, and timing anywhere in the world or near-Earth space. Not to be confused with the U.S. GPS.

Global Navigation Satellite System (GNSS) — An internationally-administered, civilian-controlled Global Navigation System currently under development.

Receiver Autonomous Integrity Monitoring (RAIM) — A technique whereby a civil GPS receiver/processor determines the integrity of the GPS navigation signals, without reference to sensors or non-DOD integrity systems other than the receiver itself. This determination is achieved by a consistency check among redundant pseudo-range measurements.

Selective Availability — The intentional degradation of GPS signals that limits the system's accuracy for non-military users.

Wide Area Augmentation System (WAAS) — A local transmission that improves basic GPS improved position/integrity information. This gives greater accuracy and integrity to basic GPS.

On GPS and Vectors
There is a built in hazard to a ‘Direct to’ GPS button and radar vectors to a specific airport. Both of these make no allowance in direction and altitude required to enter the traffic pattern. It is just as important that you arrive at an airport with regard to the pattern entry as in finding the airport.

When requesting vectors you would be well advised to request a vector to a point of entry to the 45 to the downwind rather than to the airport. In many situations it is better to find the airport to the side rather than directly ahead. The head down requirements of the GPS can make its use more dangerous than a vector that lets you spend more head’s up time

GPS Updates as Preventative Maintenance
Recorded under preventative maintenance.
Here is the section I found in the FAR's item section (c) item 32 user preventative maintenance:
(32) Updating self-contained, front instrument panel-mounted Air Traffic Control (ATC) navigational software data bases (excluding those of automatic flight control systems, transponders, and microwave frequency distance measuring equipment (DME)) provided no disassembly of the unit is required and pertinent instructions are provided. Prior to the unit's intended use, an operational check must be performed in accordance with applicable sections of part 91 of this chapter.

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