Pilotage, landfall, and dead reckoning
With the advent of GPS, getting lost is less likely, but to rely on technology is not in keeping with a fundamental tenet: Murphy's Law--"Whatever can go wrong, will go wrong." Be prepared. That's the best form of aviation insurance, and it's free.
Pilotage uses well-defined, charted references for guidance: major highways, railroad tracks, power lines, rivers, and shorelines. It seldom results in a direct route between two points, but it is dependable. In desert or mountainous terrain, where good surface references are difficult to find and GPS and VOR reception are nonexistent, pilotage may be the only way to navigate with confidence. China Lake, California, the U.S. Navy's missile test center, is one example. On several occasions, notices to airmen have stated that GPS is unreliable within 90 miles of that facility, and there is no VOR in the area.
Landfall navigation uses an offset course to reach a prominent surface feature that leads to a desired objective. Consider a flight from Kansas City to St. Louis with no GPS or VOR navigation capability. An easterly course could be flown direct to St. Louis, located on the Mississippi River, but if you did not see the city upon reaching the river, a dilemma exists. Do you turn left or right?
You avoid that situation with landfall navigation. Fly a course that is intentionally oriented north or south of St. Louis. Then, upon reaching that impossible-to-miss river, you'll know which way to turn; finding St. Louis is guaranteed on the first try.
Dead reckoning uses plotted courses, forecast winds, and computed headings, groundspeeds, and flight times. This permits direct flights between any two points. During flight training you spent considerable time preparing navigation logs in order to prove that you understood the concepts of dead reckoning. When it's mentioned after you became a certificated pilot, you just laugh and say, "No way. I use a computer-based flight planning program." And you should.
Dead reckoning navigation, however, can be greatly simplified for in-flight use if GPS and VOR navigation become unusable. To outfox Murphy if he appears in your cockpit, master the following tricks.
Before any flight, you know the forecast winds at your planned cruise altitude, but always note the winds at the lowest available altitude. If GPS and VOR become unusable, descend to below 3,000 feet above ground level in order to take advantage of sectional-chart symbology. Subdued references come alive at low altitudes.
To try this, pick two easily identifiable reference points on your sectional chart, 30 to 40 miles apart that allow a direct flight without airspace or terrain restrictions. Draw that course on your chart or fold the chart so that it's creased on the course. At intervals of six to 10 miles, circle easily identifiable reference points that lie on or near that course: isolated hills, towers, highway intersections, lakes, or other features that you can use to ensure that you're staying on course. Now take a straight edge--the edge of a checklist, for example--line it up with the course, and keep it parallel to the course as you move it to a VOR compass rose to determine your magnetic course. You may not remember this, but when you completed a typical preprinted navigation log during flight training, magnetic course was never computed.
Next, divide the wind velocity by two or by three--two if your estimated true airspeed is around 120 knots, three if it is around 180 knots. If you used two and the forecast wind velocity was 18 knots, your wind correction angle for a direct crosswind would be nine degrees. If true airspeed is more or less than 120 and the wind is not a direct crosswind, adjust the WCA using common sense. Remember, this technique is used only for short distances.
If your first checkpoint is eight miles ahead and groundspeed is close to 120 knots, it will take you approximately four minutes. If groundspeed is not close to 120 knots, adjust the time using common sense. These rough time estimates are critical.
Now, to avoid confusion, ignore the sectional chart for three minutes, maintain heading, scan your engine instruments, and look for traffic. After three minutes, you're within a minute or so of your checkpoint, so look for it. It will be there. If you've drifted off course, immediately turn back to the course, adjust your wind correction angle, and start timing the next segment.
With minimum practice, you'll learn how well this procedure works. In fact, you'll use it often, regardless of GPS and VOR capability, because it's fun to do.
Ralph Butcher, a retired United Airlines captain, is the chief flight instructor at a California flight school. He has been flying since 1959 and has 25,000 hours in fixed- and rotary-wing aircraft. Visit his Web site.
Related Articles
