A quick review of aviation's four non-GPS navigation methods
Thanks to the marvels of the Global Positioning System (GPS), most pilots these days think of navigation as no more than a sequence of button-pushing exercises. When setting up a GPS flight plan, punch in your departure airport, maybe define a few en route waypoints, name your destination, and — presto — there's your course, track, heading, groundspeed, time to destination, and even winds aloft, all on a moving-map GPS unit that can rest on your knee.
This is pretty heady stuff. But our immense reliance on GPS also contains the germ of a major problem. That problem is that many of us have more or less turned into a bunch of lazy slobs when it comes to understanding the fundamentals of air navigation. Our use of the four other alternatives to GPS navigation has also gone into the dumpster, taking with it the knowledge that we so carefully honed during our days as students preparing for our first solo cross-country flights.
Truth to tell, many of us would have to say that our basic navigation skills peaked as student pilots and have been deteriorating steadily ever since. How many of us can work a wind problem — or any other kind of problem, for that matter — on an E6-B (a.k.a. "whiz wheel")? How many can recall the procedures for calculating a compass heading to make good a ground track? What about CDI deflections at various ranges from a VOR station? Intercept angles for NDB bearings?
One of aviation's great canons is redundancy. Backup instruments, systems, and even extra engines are highly valued commodities, often formalized by regulations requiring their installation. Shouldn't pilots maintain their redundancy when it comes to navigation skills? With this in mind, let's review non-GPS navigation basics. After all, batteries can die, and GPS signal errors are not unheard of.
Pilotage
Talk about simple. Pilotage is nothing more than noting prominent checkpoints on a chart used for VFR navigation, locating them from your vantage point in the air, and flying from checkpoint to checkpoint. You can follow railroads (a.k.a. "the iron compass") from one town to the next or take the interstate (a.k.a. "IFR — I fly roads"). The trick here is to pick easily identifiable checkpoints and to remember that what looks prominent on a chart may be practically invisible from the cockpit. Solitary racetracks can make bad checkpoints. A major highway cloverleaf or junction of two rivers often is much easier to identify. By the way, altitude is your friend when using pilotage. The higher your altitude, the better you'll be able to see your checkpoints coming into view.
De'd reckoning
Yes, de'd — not dead, as in deceased, although dictionairies and most student pilot texts don't acknowledge the difference. Neither do aviation instructional texts. It's short for "deduced" and uses true course, magnetic variation, wind correction angles, and true airspeed to determine the magnetic heading and time to reach a destination. In the air, observations of groundspeed between checkpoints, together with heading information, let you determine the actual winds aloft as you fly a route.
This form of navigation, centuries old, can be uncannily accurate. The procedure begins with plotting your intended course on a chart — usually a sectional or a WAC chart, but any chart with latitude and longitude demarcations will do. The equation is: True course plus/minus magnetic variation equals magnetic course plus/minus wind correction angle equals magnetic heading plus/minus compass deviation equals compass heading. (Thus the mnemonic "True Virgins Make Dull Company.") Magnetic variation will be shown on charts by isogonic lines or marks that show the compensatory values to use when adjusting true course for magnetic course. Here, the phrase "East is least, west is best" comes into play, meaning that you subtract an easterly variation from the true course and add a westerly one.
To compute time, speed, and distance you'll need to know the airplane's true airspeed, the projected head- or tailwind component, and the distance of the leg or trip at hand. After that, it's straight arithmetic: Distance divided by speed equals time; speed multiplied by time equals distance. With a little practice on the whiz wheel, you can perform many, many other calculations — most of which you can review in any good pilot training textbook.
VHF (very high frequency) navaids
VHF navaids include the nation's — and world's — network of VHF omnirange (VOR) stations, plus the ILS (instrument landing system), localizer, SDF (simplified directional facility), and LDA (localizer type directional aid) installations that serve as means of performing instrument approaches at certain designated airports.
Though they can be used for nonprecision instrument approaches (usually to minimum altitudes and visibilities of 500 feet and 1 mile, respectively), VORs are primarily used for en route navigation. VOR signals radiate in all directions from the station. Navigating with VORs is fairly simple: Identify a radial you want to track, intercept it, and track it to the next VOR or other destination.
Got DME? Piece of cake. You not only have left-right course correction information, you also have groundspeed, distance, and ETE information as you fly to or from a VOR station equipped with DME.
VOR radials and DME can also be used for position fixing. This is done by tuning in two VOR stations and obtaining centered-From CDI readings from each. Plot the two radials on a chart, and your location is where the lines cross.
ILSs, localizers, SDFs, and LDAs also operate in the VHF frequency spectrum and provide similar left-right course guidance cues. However, their signals are much more accurate; as a result, the CDI needle is much more sensitive to off-track deviations. Tracking with these navaids means making much smaller heading corrections. ILSs give both lateral and vertical guidance. This lets you follow a very precise approach profile — so precise that ILSs can be used to descend on instruments to minima of 200 feet and one-half-mile visibility.
Non-directional beacons (NDBs)
NDBs are stations that put out signals in all directions. They operate in the 212 to 415 kHz frequency range. In the cockpit, an Automatic Direction Finder (ADF) needle points to the station. That's it. To fly to a station, turn the airplane so as to put the ADF needle on the nose, and fly on. To fly away, turn and put the needle on the airplane's tail.
While simple in theory, NDB navigation strikes fear into the hearts of the best pilots because intercepting and tracking a selected NDB bearing can be a daunting task. Also, NDBs, because of the nature of the frequency band they use, are inherently less accurate than VORs.
Again, volumes have been written about navigating with NDBs. But intercepting NDB bearings roughly boils down to: 1) turning the airplane to a heading that matches the bearing you want ot track; 2) observing the deflection angle of the ADF; 3) doubling that angle to come up with an intercept heading (as with VOR radial interception, this method won't work for bearings more than 90 degrees from your current position); 4) flying the intercept heading until the ADF needle is deflected the same number of degrees as the intercept angle on the opposite side of the original needle deflection if flying to the station, or on the same side of the original deflection if flying away from the station; 5) turning to a heading that matches the value of the bearing you want to track, then keeping the needle on the airplane's nose or tail.
As with VOR cross-radials, cross-bearings from two NDBs can be used to plot your position.
Working together
Navigation shouldn't be a sole-source task. Having all available navigation equipment turned on and tuned in to your position helps boost situational awareness and keeps you spring-loaded to keep on navigating should one of your navigation radios — or stations — quit.
Remember notams?
Check them for navaid outages, unusable VOR radials, and information about any problems with GPS or loran signal integrity. Best to learn about these before taking off, so make sure to ask your FSS briefer or scan your DUAT printouts.
When all fails
It's rare, but when problems with electronic navaids crop up, remember that signal reception from ground-based stations improves with altitude; also remember that NDB signals can be distorted when thunderstorm activity is nearby and when their signals cross shorelines.
ATC can be invaluable when your VOR or NDB equipment fails. Follow the four Cs — climb, communicate, confess, and comply — and ATC can identify you on radar and provide helpful vectors in case your pilotage or de'd reckoning skills fail you. That, or you could always consult your handheld GPS — unless you've left it behind or its batteries are dead and you don't have the cigarette lighter adapter.
What to review
Proper orientation is essential for safe VOR navigating. Fortunately, VOR instruments make this job easy. To answer that vital question — "Where am I?" — simply rotate the VOR head's compass card, using the omni bearing selector (OBS), until the instrument's course deviation indicator (CDI) needle centers and the To-From indicator shows From. A look at the instrument's course pointer tells you what VOR radial you're on. If your airplane has distance measuring equipment (DME) and the VOR station you've tuned in has DME capability, you can see how many nautical miles you are from the station. In this way, range and bearing to the station can be determined in a matter of seconds.
VORs let you navigate with a fair degree of accuracy. There are many excellent texts that go into great detail about the intricacies of intercepting and tracking VOR radials, but the general idea is to: 1) Select the desired radial with the OBS; 2) Turn the airplane to the same heading as the desired radial; 3) Observe the CDI needle deflection. If it's to the right, turn right to intercept the radial. If it's left, turn left. Fly a heading that will yield a 30- to 45-degree intercept angle to the selected radial (Note: If you are more than 90 degrees from the desired radial, this interception technique will not work and you're better off tracking radials nearer your position); 4) When the needle centers, turn the airplane to a heading that matches the value of the desired radial. Now start tracking. If crosswind components blow you to the right or left of course, the CDI will move right or left, indicating the need to apply a wind correction angle to your heading so as to recapture a centered CDI indication.
