For as long as I can remember aviation to me is the best hobby you can have while keeping your clothes on. I think I can say I know pretty much everything about the principles of flight for both fw and rotor craft. However, I can't seem to get the practice of navigation into my thick skull. I've been Googling for a comprehensive integrated A to Z guide of this subject for a long time but I can only come up with partial explanations that assume pre-required knowledge which I don't seem to have either. I have the instrument flying handbook (FAA-H-8083-15A) but that thing is so bloody tedious to read that only a monk would bother reading through if you ask me.

I'm looking for a very thorough yet practical source of information on how to use all aspects of radio navigation. I mean no disrespect but I am not interested in when something was invented, who invented it, and what that good man had for breakfast the day he came up with the idea, because these are the things I find on the net. All I'm asking for is a complete user's guide for noobs so to say.

What I do know

1. VOR+DME or TACAN transmitter (civ. or mil. but same principle) can provide the distance between aircraft and transmitter. There is also the story of the 360 radials that either point away (FROM) the transmitter or TO the transmitter but that's about the only thing I understood so far.

2. INS is an independent nav. tool that is zeroized (is that a word?) on the ground and from then on keeps track of motion changes. Comparable to the idea of a doppler radar but less sophiscated and less flawless hence not very reliable.

What I don't know

3. What is the difference between heading, course, bearing, and direction (of flight)? They're all kind of confusing.

4. The HSI. I get that my aircraft is the fixed thing in the middle pointing upwards and TO is flying to a transmitter while FROM is flying away from it but I'm afraid it ends here. What does the course knob do and what does the heading knob do? I also understand that when the CDI is moved off centre to the left I'm flying right of a certain course and vice versa. But what is that course? How does that help me getting from A to B?

5. Those radials. I don't want to either fly along a radial TO or FROM a station, I want to fly my own route that possibly crosses every radial but does not follow one. Example, I want to fly from west to east in a straight line, but that line is 50km north of a transmitter. So I will fly parallel to the radial from 270 to 90 but I'm 50km off to the left of that radial. How do I do that? How is VOR+DME going to help me?

6. Let's say just now for the sake of simplicity I am flying away from a transmitter between the 40 deg. radial and the 41 deg. radial. When I'm 10km away from the transmitter that gives me a little margin. But when I'm 250km away that margin gets quite large. How do I know where I am when I'm neither exactly on the 40 deg. radial, nor on the 41 deg. radial?

7. Every source I can find is talking about flying along radials. The chance that my flight route is exactly aligned with a radial is what, 0? Which essential bit of info am I missing?

Thanks to those who are willing to help me out. Even if I sound like a total moron.

Really really low time real life VFR (not IFR) pilot here, so take what I have to say with a little more than a grain of salt...

3. This link explains it rather well: http://www.askacfi.com/86/true-course-magnetic-course-magnetic-heading-compass-headinghelp.htm

The gist is that you have to convert the direction of flight that you planned on a map into the heading you point your nose towards via compass. Along the way, you have to account for magnetic deviation, variation, and wind drift (using your handy E6B slide rule). You do this for every leg you fly to minimize drift (You'll still get to your VOR waypoint if you don't crab, but you'll take a curving path that will burn more fuel and eat time).

4. The HSI basically tells you which way the VOR transmitter is. The CDI shows you how far off the heading is from directly to/from the VOR transmitter. You can't really tell how far off course you are from the offset.

5. You actually have to know whether you are flying to or from the transmitter even if you are not pointed at it. Otherwise you can be flying one of two possible directions.

6. You can't on one radial. One degree difference is highly difficult to tell (The checkride test for Instrument rating allows you up to 10 degrees of error). The best way would be to dial into two separate VORs and fly directly towards one and away from another. If you start to drift off course, you'll be able to see the angle difference between the two. That, and if you're flying blind, the ATC controller will tell you.

7. The radial is just the direction to/from a VOR. You don't need to fly directly to or from it. However, you can still use two separate VORs to triangulate your position by dialing into two of them, turning your VOR heading knob until the needle centers (which tells you which direction the VOR is) on both, and then going to your map, and drawing lines out from the VOR at those headings. Where the lines intersect is where you are.

The way I learned to flight plan via radio navigation is to make your waypoints VOR transmitters, so you are either flying to or from a transmitter if possible.

That and you set up what are called VOR intercepts, in which you set your second VOR receiver to a different VOR and set to a certain radial. When the CDI swings past center, you can look where that radial intercepts your course (this is preplanned on your flight plan) and know where you are on a particular leg of flight.

I've found radio navigation to be pretty confusing stuff that, unfortunately, can only be oriented by having good spatial orientation, thorough flight planning, and keeping track of everything via a good kneeboard. If you want to get into it, I'd highly recommend reading a Private Pilot or Instrument Ground School textbook as I'm sure I'm doing a sham of a job of explaining it.

That, or just use GPS instead...

Be careful what you ask for.

http://www.faa.gov/library/manuals/aviation/media/FAA-H-8083-15B.pdf

For your questions, I'd skip to Chapter 9, though there is a ton of good stuff in the previous sections.

What I can offer for the rest:

1. TO/FROM is confusing if you try to over think it (which I am about to do so God help me). The radials don't "point" in any direction necessarily. They shoot out from the station in 360 degrees. The To/From part really just tells you if you are in the same 180 deg wedge as the radial you have selected. For me it's much easier if you already know where you are, which you hopefully should since you know where you parked your car. If I take off from New York and head south to Washington, I can in theory select the Washington VOR and select the 180 deg radial. I will get a TO indication which makes sense...I'm heading south TO the VOR. If I forgot my keys and need to turn around, it would still show TO even though I'm heading away from the station (if I left the 180 deg radial set in the VOR). But, naturally, it would make much more sense to dial in the 360 deg radial since that's the way I'm going. The VOR would then indicate FROM. The harder part is when you try to find yourself if you are lost. Hopefully though, you are never so lost that you can't figure out which set of cross radials makes sense.

You did say you already know this, so I apologize for repeating it. But the point I was trying to get across is that navigation is a thousand times easier if you apply the rule that if it doesn't make sense, you are probably doing something wrong.

2. Zeroized is a word. Look on almost any piece of crypto gear (like a military IFF). It's one of those military words that usually are defined by a much simpler word that should have just been used in its place (See "orientate"...means "orient"). From a very basic pilots' perspective, an INS is just a set of gyros on a platform. You tell the INS box where you are and it levels the platform to local up and down. Once leveled, accelerometers on the platform sense any acceleration and turn that measurement into a speed. The speed equals displacement and so the INS keeps track of where you are. But, since you aren't actually attached to anything, the gyros will drift slightly and so you will begin to pick up errors. To counteract these errors, crews will update the INS position either by overflying a known point, automatically by using cross VOR DMEs, or through GPS. There are all sorts of nav setups so they aren't easily categorized. Even GPS isn't generally sufficient for precision approach criteria and so GPS may be augmented by a Space Based Augmentation System (SBAS also known as WAAS) or a Ground Based Augmentation System (GBAS also known as LAAS). SBAS and GBAS correct for GPS errors to allow for "ILS like" accuracy. There; you know more than most pilots now! LOL!


Much of the rest can be found in the book, but here's a short (or as short as I can manage ) version:

3. These are often confusing in that they are often used interchangeably (and often incorrectly). My best explanation..

Heading - The direction that the aircraft is pointing. Could be True or Magnetic.

Course - More refers to the way the aircraft is "going" rather than "pointing" or possibly where it is intending to go. ATC's direction to "proceed on course" means stop following the heading you were assigned and begin navigating on your own. Hence, you can be "off course" if you are on your calculated heading but the wind is blowing you sideways off the assigned radial.

Bearing - Usually means where something is in relation to you or vice versa (most likely from the word "bear" as in "that French frigate BEARS two points off the port bow"). That's why the VOR instrument has an Omni Bearing Selector. If you center the needle with a TO indication, the number in the OBS is the bearing TO the station or the station BEARS on the heading that is shown in the OBS. If you intended to fly that bearing to the station, then you can turn until your HEADING matches the BEARING and you will fly "ON COURSE" over the VOR assuming no wind. If there is a strong wind, you may be blown "OFF COURSE" or your COURSE(in this case the word "ACTUAL" is sort of implied) may be taking you to the left or right of the VOR. So you may need to hold a HEADING to the left or right of the selected BEARING to hold you ON COURSE(maintaining a ground track on the bearing to the VOR).

Direction of Flight - Mostly used generically. Direction of flight may be used to select a cruising altitude (0-179 deg EVEN altitude. 180-359 deg ODD altitude) or as an ATC tool (e.g. eastern departures from Denver should expect to take off from the eastern two runways and western departures should expect the western two runways...for obvious reasons).

4. Much better explained in the book. Aren't you thankful I'm not going to drone on and on about it?

5. Welcome to old school radio navigation! Thought you were going to fly straight, did you? If you want to be really frustrated (and I can't imagine why you would) pull out the low or high altitude airway chart for the eastern United States and try to fly east or west on airways...not easy. In these cases, your only other option is to file VOR to VOR or VOR to intersection (and vice versa). Then, instead of listening to the melodious tones of the Clearance Delivery controller saying "Cleared as filed", you get to hear the dreaded "prepare to copy full route clearance" when they stop laughing at your requested route and give you one more in keeping with their plans.

6. An understandable question but a bit of "measuring with a micrometer, marking with chalk, and cutting with an axe". First of all, google "VOR Service Volumes" and you'll see that you are not likely to be 250km from a VOR and still pick it up. This isn't wholly true as, if you are up there in altitude, you might just receive it. But you aren't technically supposed to file between two VORs that are that far apart and virtually every airway ensures both obstacle clearance and signal reception as long as you are above the Minimum En route Altitude (MEA) depicted on the chart. Also, practically speaking, since the VOR instrument is picking up a radio beam and the radio beam is expanding as the distance away from the station increases, the VOR instrument doesn't really know precisely where you are either.

That's why most routes have tolerances appropriate with the route type and leg distance. In fact, GPS navigation brought up unforeseen new issues as aircraft that had previously been distributed around an airway were suddenly all flying along the same line in the sky. True, the aircraft were separated by altitude, but flying only 2000ft (now 1000ft with RVSM) below a heavy like a 747 has the potential to be a rough ride!

7. Largely answered in 5 but, for radio nav, you are ALWAYS flying along radials. If you are flying along an airway, that's self evident. But, even if you are going to fly VOR to VOR or VOR to fix or VOR to intersection (and to reiterate VOR/ADF referenced flying is the only method of RADIO Navigation) you are going to select a radial and fly down it. If you don't, and you just put the "needle on the nose" which is an old fashioned way of saying centering the needle and heading toward the station, any crosswind will make the needle drift to the right or left. Then you might decide to center the needle again by selecting a new bearing with the OBS knob, but if there is still a crosswind it will drift some more. If you keep doing this you will sort of inscribe a big question mark around the station as you continually keep pointing the nose at the VOR. If, on the other hand, you select the direct bearing to the station and fly towards it using whatever crab angle into the wind is required to keep the originally selected bearing needle centered, you will fly a straight line to the station.

Sorry again if that is much more than you wanted to know.

Deacon

both, but deacon especially, thanks for the clarification so far.

what caused a great confusion at my side is the fact that every child is taught that flying is the ultimate freedom, there are no roads you have to follow. so i was thinking, it cant be i understand radio navigation correctly because that would mean im limited from flying pre set routes in the form of routes between stations and routes starting/ending from an intersection. but after the above that seems to be the harsh reality if you solely depend on radio beacons.

im at my phones browser so browsing is not that comfortable. i will google what youve told me to in order to aid my understanding of the matter tomorrow at my notebook.

It's what everyone thinks, myself included when I started flying.

There has been a certain progression of instrument flying over the years. I believe the first nav beacons were actually powerful lights that shone straight up. Later, there were the non-directional beacons (NDBs) which were inaccurate, had no "radial" capabilities, and were more art than science to operate when they were first introduced. VORs were a huge step forward, but originally were not automatically DME capable and so one had to fly in on a radial, fly out on a radial or occasionally use the intersection of two radials to define a point (it's actually the reason you have two NAV radios...to fly out of a radial on one until you reach the crossing radial on the other or to find yourself if you were lost which becomes somewhat redundant when you get DME).

The need to integrate and upgrade the airspace system and the circuitous path that took has led to the network of navaids and airways that exist today. INS was a great leap ahead for long distance navigation, but never did away with the need for this navigation network, not least because not everyone could afford one. It wasn't until GPS was relatively affordable that there could be an effort to make navigation more direct.

Deacon

By the way, basic math tells me that in order to triangulate an intersection between radials to set a steerpoint, I have to at least tune in at two VORs/radials simultaneously. Right?

Opening FAA-H-8083-15B.pdf right now...

Well, more or less.

My answer is probably at least a little dated, since I haven't flown true Radio Nav in a long time. Historically, an intersection had to be defined off two Navaid radials, because DME wasn't common...or at least not common enough. But if you don't have DME, then the intercept geometry of navigating to an intersection is pretty much voodoo magic since you basically need to swag a heading that seems about right, then judge the movement of two separate VOR needles and adjust so that they center close to simultaneously. I don't think I have ever been cleared to do this.

DME technically changes things, since you now have a radial and a distance, thus you could define a point with one Navaid. Most points don't exist in space by themselves though. They are part of an airway or procedure and so you will generally see them defined both ways. The exception to this is something like an Initial Approach Fix (IAF). Old style VOR procedures will generally start atop the VOR since, like NDBs you don't know how far away you are. Newer style VOR/DME like old style TACAN (which has always had DME) may have the IAF not co-located with the Navaid. Still, if you were required to free Nav to a point in space, you were still swagging at best.

If you had an aircraft equipped with an RMI (the compass card thing with the two needles on it) you could sort of use it to plot a course to a Navaid DME point, but it was still very much an art. If, like most Cessnas, you only had your two VOR indicators and perhaps a DME, you were again largely left with making a great big guess.

As such, (and this is the part that reaches back into my memory a bit) you would seldom be sent to a point in space by ATC without further guidance if they knew your aircraft didn't have the capability to navigate to these points accurately (as defined by the equipment code on your flight plan).

What you would get was probably this:

"Cessna N472, fly heading 240. Intercept the ADW 090 Radial inbound, you are cleared for the VOR/DME approach to Runway 01R. Report commencing."

So, the controller has set you up on a heading that he knows will have you intercept the 090 radial into ADW BEFORE you reach the IAF. Once you intercept the radial, it's a simple matter of watching the DME to determine when you have reached the IAF. If, on the other hand, he let you free Nav over to the IAF, there is no guarantee you wouldn't reach the radial AFTER the IAF. And then you have to decide whether you will turn around and fly back to the IAF and start the approach or start the approach late and begin descending once you are on a published segment of the approach.

Now, aircraft with GPS or INS, can and are cleared to fly to any point including the IAF, even if the GPS isn't certified to fly approaches. This is the world most high end (and increasingly low end) aircraft inhabit. So, slowly the old ways change from what I had back in my Cessna days.

Deacon

This is a great thread!

JP, you mentioned a couple of things that I would like to expand upon.

The first, is talking about "not having roads." Ironically, there are IFR "roads" in the sky, and they tend to go between navaids for reasons already specified (i.e. much easier to fly directly to a navaid rather than an intersection or range and bearing). On IFR low altitude charts (below 18000ft in CONUS) they are known as "Victor Airways" ("Jet Routes" above FL180), and IFR flight plans are simply a string of 3 letter navaid identifiers and 5 letter fixes (generally intersections between navaids, though with DME to each navaid indicated as well). Since most simple general aviation aircraft don't have the RMI and instead use two CDIs (and one with DME), flying between navaids is the easiest way to fly IFR. You can also fairly easily fly from navaid to fix to navaid, but flying "point to point" , or between fixes with two CDIs is impractical (it's doable with RMI, but still something of an art form).

Second, most inertials are reliable, though with a tendency to drift over time. Depending on the model and maintenance, advertised drift can be up to 2 miles per hour of flight, though my experience was closer to 0.5-1 mile per hour. The best thing about the INS is that it is a completely self-contained navigation system, so that it cannot be subject to MIJI (meaconing, intrusion, jamming, and interference), and it is the primary source for overwater navigation. Even if the INS drifts 10 miles after a 5 hour flight, it's still close enough to get you to a navaid, at which point you can "fly the needles".

I'm starting to get it now.

All the time I was thinking: OK beacons are nice and all to fly to, but why would I want to approach or leave them from a certain bearing? Why not fly from beacon to beacon to beacon until I reach my endpoint of choice? But since flying from intersections and flying along certain preset direction either to or from a beacon is the way to go when INS and GPS is not an option, I now see the importance of 'radial-enabled' beacons in the form of VOR/TACAN vs. 'non-radial-enabled' beacons like NDB.

There are other benefits to airways that probably ensure that they won't disappear entirely.

1. First of all, they route traffic around Special Use Airspace. SUA are huge and often bizarrely shaped blocks of airspace that may either require permission to enter or may at least occasionally have other aircraft doing funny things in them. They top out at different altitudes, but it will be one more thing controllers need to worry about when everyone and their sister starts "going direct".

2. They "funnel" traffic. If you were to have a dozen or more aircraft approaching your airfield more or less simultaneously from near infinite directions, it would be difficult to know exactly who will get there when. By routing aircraft along airways and onto standard arrivals, you can "direct traffic" as it were. Even still, aircraft must often be vectored or be assigned airspeeds for deconfliction. Perhaps one day every aircraft will be able to be computer calculated so that there is never a need for deconfliction (so called 4D navigation, the 4th D being time) but that is currently not possible today. It's really an infrastructure thing.

Regarding having to fly direct to a navaid and then outward or vice/versa:

Things have changed considerably even in the GA sector with the introduction of GPS/RNAV and now WAAS. In particular, you can file direct to just about anywhere, and there are GPS approaches in many places that you'd never seen with an ILS.

When I did my instrument rating I insisted on learning in an airplane that had an ADF, so I would at least have the assurance that I'd be able to do an ADF approach if I absolutely needed to. But you will find that these days, there is a huge reliance on GPS and GPS approaches with WAAS (LPV) in lieu of ILS.

ILS is 1930s technology, after all.

By now I did some more researching myself and I was about to conclude the thing you just said.

All the above answers have been quite helpful and the matter is much more clearer by now. In A-10C it's mostly using EGI and TACAN for an approach but still, I wanted to know all the basics before blindly relying on more advanced systems.

Thanks for the input Headspace!

I'd be very interested in what and where you are flying. Are you saying that you are not being assigned airway navigation anymore or that you are not using VORs to do it? If you are getting true "You are cleared to KXXX airport via direct" what area are you flying in and how long is the trip distance?

My current experience is primarily with the airlines these days, so trends in GA flying are more of a mystery to me. Airlines are still being routed via the airway system whether the aircraft is GPS equipped or not. It is common, however, to get a clearance direct to some point downrange once you get to talk to a high altitude center controller. I would suspect by consequence that most corporate aircraft that fly into air carrier serviced airports would be required to do the same.

I think that GA aircraft flying between smaller airports are probably really reaping the benefits of RNAV/RNP.

Air carriers though, many of whom still achieve their lowest mins via CAT III ILS (50ft or lower), will remain reliant on ILS for several years to come, simply because its cheaper than upgrading their equipment. Still, with airlines like Continental/United getting certified for GBAS, it certainly seems the shape of things to come.

I'd be curious to hear from Beach, who flies Kingairs and Citations what his recent experience has been.

Interesting stuff.

Deacon

Deacon:

Single piston, lately it's mostly PA-28, either the -181 or -161. I usually file as P28A/G because it gives ATC the most flexibility and it effectively says "I can accept direct."

You are probably right about GA being the primary beneficiaries of RNAV. When we file, it's really not a matter of being assigned airway navigation, but following the trends that you see from ATC. I don't want to file and have them switch it on me, so I look at what they're assigning before I file (unless I want an airway route for practice or something, and then I will ask). The direct route almost always makes sense because it's the most fuel efficient. You can check on sites like fltplan.com what the last assigned routes were for any given destination.

It would be my guess that airlines are being routed via the airway system because you go to fewer destinations than GA and private pilots, and the sequencing is way more regimented. You know you will arrive and depart via specific arrivals and departures, you plan for specific routes--it works smoother when everything is the same. That would be my conjecture. But you do have GPS routes, at least as far as the IFR-HI charts are concerned. Whereas a private pilot is liable to file for who knows what, and say NO SID/NO STAR on top of that.

As far as the ILS is concerned, you are absolutely spot on. But then again, you are going into and out of the same smaller set of class C and B airports that have ILS. Technically the LPV approach isn't a precision approach like ILS is--it has its own "approach with vertical guidance" category. I don't know what the logic is behind that, and the distinction doesn't serve much of a purpose in the practical sense since the minimums are CAT I-ish. But as far as filing is concerned, the fact that it isn't a precision approach can affect choice of alternates.

I strongly recommend this site: http://www.navfltsm.addr.com/

Explains all the principles, easy to understand, nice step by step and entertaining for flight simmers.

Nice and easy indeed. Strange I did not find that site myself.

Well, that's pretty cool that you can actually file (and have a reasonable expectation of receiving) a direct flight plan! I would think that in more congested areas, like the Southwest US between Phoenix and San Diego say, they still route GA along airways...there are restricted areas all over the place. But hey, if there are no obstacles between you and your destination, why not allow filing direct.

I think you hit the nail right on the head with commercial traffic. With the conga line that is usually streaming into Chicago, LAX, or JFK, the controllers start racking and stacking you way the hell out there. Direct to the Final Approach Fix just isn't going to work...yet.

ILS (and NAVAID) decommissioning is going to be a delicate process. I worked in DC for the Air Transportation Division for awhile and there is an ongoing battle to drag the National Airspace System into the 21st century. With everything from Piper Cubs to 787s out there, it's hard to come up with an upgrade plan that isn't going to leave someone out in the cold.

You're already seeing the beginnings of that upgrade. As you said, NDBs are going away as are VORs and their approaches. With RNAV/VNAV and LPV approaches, airfields that used to have one crummy circling approach off a non co-located VOR now can have CAT I like mins.

ILS will come along thereafter I think. The real trick as I said will be to get the airlines down to their current CAT II and III mins without scaring them off by the upgrade costs.

But sooner or later, planes will be free from ground based navigation.

Well, almost. As I understood it from speaking with the Nav guys, there will remain a skeleton of ground based NAVAIDs out there to preclude intentional or accidental satellite disruption from shutting down the national airspace system. Thus I would think that at least some categories of aircraft will be carrying an ILS/VOR receiver for some time yet.

Great conversation!

Deacon

Nice find Hans!

INS is the primary mode of navigation on aircraft equipped with it, even if an aircraft is equipped with GPS. The system is extremely accurate with time being the "enemy" as the system can drift over long periods of time (though I have seen some aircraft return with very little drift). The word zeroize is used to mean erase usually confidential/classified information on certain systems which contain vital information. The word you are looking for is intialize as the INS is intialized to the present position by entering the LAT/LON coordinates at start-up. The coordinates are usually placed somewhere the pilot can easily see it like on the outside of a terminal (or on the wall inside a bunker). If a pilot does not allow enough time for a complete alignment, or if there is lots of aircraft movement during alignment, this can cause large drifting errors. Ring Laser Gyro (RLG) systems are less prone to errors.

You're welcome, and you don't sound like a complete moron...