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Copyright © 1996-2005 jsd


14  Cross-Country Flying

I’m not lost, I’m just uncertain of my position.

The term cross-country flying refers to essentially all flying that takes you beyond the immediate vicinity of the airport.

In cross-country flying, a number of basic skills assume added importance. For example,

14.1  Pilotage

The term pilotage refers to finding your way by reference to landmarks. This is a basic yet important pilot skill.

From the air, things look different than they do from the ground. It will take you a while to learn aeronautical pilotage skills. The rest of this section covers miscellaneous small hints.

14.1.1  Airports Make Good Landmarks

When you are planning a cross-country trip, it is advantageous to plan a route that passes over airports along the way. They make great checkpoints.

Airports make good landmarks.
     

If you fly over an airport, it is hard to mistake it for something else. Indeed, many airports have their name printed on one of the taxiways in twenty-foot-high letters, which pretty much eliminates all doubt as to where you are.

Even if you are not using the airports as navigational references, it is a great exercise to practice spotting all the little airports along the route. This is not easy; it is an acquired skill. Airports with grass runways can be particularly challenging, since it is hard to distinguish them from the surrounding fields. Hint: Look for the airplanes. If you see lots of airplanes parked on the grass, there’s probably a runway nearby.

If you stumble across an airport that doesn’t correspond with where you think you are on the chart, it probably means you are off course, but not necessarily. That’s because some private strips and military fields are intentionally omitted from the charts.1

Spotting airports at night is sometimes a challenge. Non-pilots often have the impression that airports ought to be brightly lit, but in fact they are not. An airport in the middle of a town will be about the darkest thing in town.

Major airports have fairly bright runway edge lights, but the lights are highly directional, so unless you are near the final approach course you may be unable to see them. Also note that the tower has control of the runway lights, and may well turn off all the lights on whatever runways are not being used at the moment.

Most airports have rotating beacons that flash white and green, alternately. However, it is surprising how many airports have no beacons, inoperative beacons, or beacons that are so dim as to be useless.

Airport-spotting skill might come in very handy if you ever need to make a landing on short notice.

14.1.2  Choose Distinctive Landmarks

In parts of the world where there are relatively few lakes and rivers, they make good landmarks. In other parts of the world, there are so many lakes and rivers that it is distressingly easy to misidentify them.

Similar words apply to highways: if there are a lot of them, their usefulness as landmarks is impaired.

In forested areas, highways and railroads have the additional problem that you may not be able to see them unless you are nearly overhead.

Some landmarks (like airports, small towns, small lakes, etc.) are essentially point-like (zero-dimensional). Other landmarks (highways, railroads, coastlines) extend a long way in one dimension. In the latter case, you can readily see that you are somewhere along the landmark, but you will need additional information to know where along the landmark you are. Suggestion: the intersection of two one-dimensional landmarks makes a fine zero-dimensional waypoint.

14.1.3  Doglegs

When planning your first few cross-country trips, rather than planning to make a beeline from departure to final destination, plan a dogleg course that passes directly over a goodly number of airports and other landmarks along the way.

In general, if there is a long stretch without a 100% obvious landmark, plan a dogleg so that there is. Especially on hazy days, this simplifies life.

Even a rather crooked dogleg (say, 20 degrees off the beeline heading) adds only a few percent to the length of the trip.

14.1.4  Reality-Based Navigation

When you are at home, planning a flight, it makes sense to look at the chart and try to pick out a set of convenient, conspicuously-charted objects. This is called map-based navigation: you go from the map to the reality.

On the other hand, when you are in the plane, it makes a lot of sense to reverse the process: Look out the window and find some conspicuous object, and then see if you can find it on the map! This is called reality-based navigation: you go from the reality to the map.

14.2  Dead Reckoning

The term dead reckoning refers to navigating by keeping track of time, rate of travel, and direction of travel. To do a good job of dead reckoning, you need three instruments:

In addition, you will need decent estimates of wind speed and wind direction.

Before discussing the theory of this, let’s do an example. Let’s suppose you are airborne at 5000 feet, cruising at 110 knots (indicated airspeed) on a heading of 090 degrees. At 32 minutes after the hour, you arrive over Hackettstown, New Jersey, and your next checkpoint is Sussex, New Jersey. The “winds aloft” forecast called for winds of 335 degrees at 25 knots. You need to know what heading to fly and how long it will take to reach the next checkpoint. The calculation that follows is a rough estimate that you can do in the cockpit. (Later on we’ll see how to do more exact calculations in the peace and quiet of the flight-planning room.)

hack-sussex
Figure 14.1: Course Line from Hackettstown to Sussex

First of all, note the time. Write it on the chart near Hackettstown, as exemplified by the red “:32” marked on the chart in figure 14.1. (Use a pencil, so that you can erase and re-use the chart for your next flight.) While you are there, draw a line from there to the next waypoint (Sussex). This line, too, is shown in red in figure 14.1. Look outside, checking for traffic.

14.2.1  Course

Next, you should estimate the course from your present position to the next waypoint. To do this in the cockpit, use your hand as follows: put your thumb on your present position (Hackettstown) and your long finger on the next waypoint (Sussex). Now move your hand (without rotating it)2 until your thumb is at the center of some nearby compass rose. In this case, the Broadway VOR3 is convenient. Now look along the line from your thumb to finger, and see where it crosses the edge of the compass rose. In this case we find that it crosses at the tickmark that corresponds to 040 degrees, which we take as our approximate magnetic course.

In the absence of other information, this approximate course is your best estimate of the proper heading. This may not be exactly your optimal heading, but it is a reasonable approximation, certainly better than maintaining your previous heading. Turn promptly to your best-estimate heading and maintain it while carrying out the next steps of the calculation. If and when you have information about crosswinds (section 14.2.3) and VOR twist (section 14.4.4) you can refine this estimate. Check for traffic again.

14.2.2  Distance, Time, and Airspeed

When looking for a waypoint, such as your destination airport, it doesn’t do you much good to be on course if you have already inadvertently passed the waypoint. Therefore, it is vital to know how far you have progressed along the course. This is just as important as staying on course, and perhaps not as easy. Consider the contrast:

Note that the distance error involved in the second case is many times larger than in the first case.

To say it another way, it is easier to notice an unforecast crosswind that is blowing you left or right of course than it is to notice an unforecast headwind or tailwind that is messing with your progress along the course.

To keep track of distance along the route using pilotage, you need an estimate of your groundspeed. Then, given speed and distance, you can figure out how much time it will take to get to the next waypoint.

The first step is convert indicated airspeed to true airspeed. In this case, 110 KIAS is about 120 KTAS.4

The next step is to account for the wind. We need to resolve the total wind into a headwind component and a crosswind component. We will use the face of the directional gyro as an analog computer to help solve trigonometry problems.

Recall that the wind was out of 335 degrees at 25 knots. Since these forecasts always use true azimuth, you need to convert 335 true to 347 magnetic. (Notice how the compass roses on the chart are rotated relative to true north if there is any doubt as to the sign and magnitude of the correction.) Now find 347 degrees on your directional gyro. It will be at about your 10:00 position, as shown in figure 14.2. Now we are going to use the circular face of the DG as a map. We choose the scale factor such that the radius of the DG represents the magnitude of the total wind, 25 knots in this case. Imagine a vector from the “347 degrees” point on the DG to the center. This represents the total wind, as shown in red in figure 14.2.

dg-wind
Figure 14.2: Wind Calculation using Directional Gyro

The headwind component is represented by the projection of the wind vector onto a line that runs vertically across the face of the instrument (from your 12:00 position to your 6:00 position), as shown in yellow in figure 14.2. In this case its length is about 3/5ths of a radius, which represents about 15 knots. Therefore your groundspeed is about 105 knots (true airspeed minus headwind component).

Now, we need to estimate the distance of this leg of the flight. There are two ways to do this.

Method one is literally the rule of thumb. The length of my thumb (from the last joint to the end of the nail) corresponds to ten nautical miles on sectional charts, almost exactly. You can calibrate your own thumb. In this case, the required distance is about two and a half thumbs, or about 25 nm.

Method two is sometimes more accurate. Again put your thumb and finger on Hackettstown and Sussex, respectively. Now move and rotate your hand (without changing the distance between thumb and finger) so that you can use the tick marks on one of the north-south grid lines of the chart as a reference. One minute of latitude is one nautical mile.5 Again the answer is about 25 nm.

It is easy to remember that a groundspeed of 120 knots corresponds to two miles per minute. At that speed, you would be there in 12.5 minutes. However, in this example your groundspeed is about 10% slower than that, so it will take about 10% longer, about 14 minutes. You therefore expect to pass over Sussex at 46 minutes past the hour.

14.2.3  Crosswind Correction

Now we are going to calculate the crosswind component. Again we will use the face of the DG to help solve the trigonometry problem.6

Recall that the wind was out of 335 degrees at 25 knots, represented by the red vector in figure 14.2. The projection of this vector onto line that runs horizontally across the instrument (from your 9:00 position to your 3:00 position) represents the crosswind component, as shown in blue in the figure. The length of this component in this case is about 4/5ths of a radius, which represents about 20 knots. That is, we have a crosswind component of about 20 knots, from the left.

To convert the crosswind velocity component to a crosswind correction angle, you can use the information in table 14.1.7 In the present example, you should turn the airplane 10 degrees to the left of course,8 that is, to a heading of 030 degrees (heading = course + wind correction).


GroundspeedGroundspeedCrosswind Correction
(knots, real)(knots, pi=3)(knots per degree)
 57  60 1.0
 85  90 1.5
115 120 2.0
145 150 2.5
170 180 3.0
Table 14.1: Crosswind Correction Angle

If you are off course, apply an intercept angle (heading = course + wind correction + intercept) as discussed in section 14.3.3. The heading problem is now solved.9 Check for traffic again.

14.2.4  The Wind Triangle

Concept #1: According to Galileo’s principle of relativity, you cannot measure a velocity by itself; you can only measure the velocity of one thing relative to another.

Concept #2: Velocity is a vector; that is, it has a magnitude and a direction. (In contrast, something that has only a magnitude, without direction, is called a scalar.)

There are three velocities involved in dead reckoning, as illustrated in figure 14.3, and as shown in table 14.2.


Vector=Magnitude&Direction
airplane velocity=airspeed&heading
relative to the air    
airplane velocity=groundspeed&track
relative to the ground   direction
air velocity=wind speed&wind
relative to the ground   direction
Table 14.2: Relative Velocities

wind-triangles
Figure 14.3: Wind Triangle + Headwind and Crosswind

Note that the word velocity always refers to a vector, while the word speed always refers to the corresponding scalar magnitude; see section 19.1.4.

If you want to draw an accurate wind triangle, you must be careful to draw the headwind and crosswind components as projections along and across your course as is shown on the right-hand part of figure 14.3. (It is a common mistake to draw them along and across your airspeed vector instead.) With the help of such a drawing you can understand why a direct crosswind (that is, a wind directly perpendicular to your course) will slow you down a little bit: even if there is no headwind component, your groundspeed (the base of a right triangle) will be shorter than your airspeed (the hypotenuse).

Also you can see that the airplane is pointing into the relative wind but it is moving along the course — which are two different directions.

14.2.5  Discussion

Note that in the scenario presented above (section 14.2) there was basically no alternative to using the quick, approximate dead reckoning techniques (section 14.2.2 and section 14.2.3) for choosing the heading. Consider the possible alternatives:

Flying involves at least some dead reckoning all the time. Even if you are relying on instruments for long-term navigation, you can’t be looking at the CDI all the time, so in the short term you are just using dead reckoning, i.e. just holding a heading.

Even on IFR flights, dead reckoning is important. Sometimes it’s merely a convenience, and sometimes it’s absolutely required; procedure turns and holding patterns are familiar examples.

14.3  Navigating by Instruments

14.3.1  Don’t Be a Gauge Junkie

Navigating by instruments does not relieve you of your responsibility to see and avoid other aircraft.

A seemingly-nice fancy GPS can get you into trouble. It is altogether too common for pilots to spend too much time fussing with the GPS when they should be flying the airplane. Hint: on a typical GPS, 90% of the value comes from 10% of the features, so don’t knock yourself out trying to use features you don’t really need.

A plain old VOR receiver can get you into trouble, too. It is altogether too common for pilots approaching a VOR to have their heads “down and locked” — paying vastly too much attention to the Course Deviation Indicator (CDI) needle and not enough attention to other traffic. The more accurately you fly over the VOR, the more likely you are to run into somebody else who is trying to do the same thing.

Keep track of your position on the chart. This will be much easier if you have drawn your course-line on the chart as discussed in section 14.8.

14.3.2  Navigation Systems (Brief Survey)

Navigation systems in common use for cross-country flying include:

The principles of operation of these systems will not be discussed in this book.

14.3.3  Intended Heading

On cross-country flights, I repeatedly ask my students the following question: “What is your intended heading, and why?”

The answer to the “what” part of the question depends on circumstances, and will be a simple number such as 035 degrees for example. The “why” part of the question is easy; the answer is always the same, so you might as well memorize it right now:

Heading = Course + Wind Correction + Intercept
     

By way of example, suppose the course is 040, there’s about 20 knots of crosswind from the left, and we’re cruising at 120 knots. That makes a ten-degree crosswind correction, so if we are on course we will stay on course if we fly a heading of 030 (i.e. 040 − 10).

Now suppose we are about 10 miles from the station, and the CDI is one dot off to the right. That means we need to apply about 5 degrees of intercept angle, and hold it for a couple of minutes. Therefore the intended heading should be 035 degrees (i.e. 040 − 10 + 5).

Note: When I ask for the intended heading I want you to tell me your intended heading. It has almost nothing to do with the present actual heading. You should be able to answer this question immediately ... and without looking at the DG. (If I had wanted to know the actual heading, I would have asked a different question.)

At the earliest opportunity, you should figure out the intended heading for the current leg of the flight. Make a mental note of it. Then from time to time, look at the DG. If you ever see that the actual heading is not equal to the intended heading, promptly turn to the intended heading.

The course is fixed by basic considerations of where you’re trying to go. The wind-correction angle is determined by procedures discussed in section 14.2.4. So let’s now discuss the intercept angle.

A ten-degree intercept angle is usually plenty. If you are a mile off course, a ten degree intercept angle will get you back on course in less than 6 miles, which should be just fine for typical enroute navigation. As you get better at navigation, you will be able to detect smaller off-course distances (say, half a mile), in which case a smaller intercept angle (5 degrees) will be appropriate. Small corrections are the mark of a pro.

If you are farther off course, say 2 or 3 miles, you can still use a ten degree intercept angle, which will get you back on course in 12 or 18 miles. If for some reason you need to be back on course sooner than that, you can use a larger intercept angle.

Usually, the reason you are off course is because you didn’t do a very fastidious job of maintaining the correct heading over the last few miles. In such a case, the solution is straightforward: choose the right heading (course + wind correction + new intercept angle) and maintain it.

In other cases, you might have been blown off course by an unexpected wind. In such a case, you might want to revise your estimate of the crosswind correction angle. Therefore the intended heading will be course + revised wind correction + intercept.

14.4  VOR Techniques

Nowadays practically anybody who can afford to have an airplane can afford to put a GPS in it. Still, though, you don’t want to let your VOR navigation skills atrophy completely.

14.4.1  Off-Course Distance

The Course Deviation Indicator on a VOR receiver indicates the off-course angle (two degrees per dot). If you know how far you are from the VOR, you have to do a little work to figure out the off-course distance.   In contrast, on a GPS the CDI reads directly in miles and fractions thereof ... which is usually what you care most about.

The simplest way is to look at the chart. If you are ten miles from the VOR, the distance between tick marks on the compass rose tells you immediately what distance corresponds to a five-degree off-course angle. If you are nearer or farther from the VOR, the off-course distance (for any given angle) is proportionately smaller or larger.

The other way is to use arithmetic. Suppose you are 57 miles from the VOR. Since there are 57 degrees in a radian, at this point each degree of off-course angle corresponds to one mile of off-course distance. At this point (57 miles from the VOR), a three dot deflection corresponds to being six miles off course, which is embarrassingly poor navigation. In contrast, suppose you are only a couple of miles from the VOR. Then the same CDI deflection (three dots, which is six degrees) corresponds to being off course by less than a quarter mile, which is perfectly fine navigation.10

Bottom line: when you are close to the VOR, do not overreact to small CDI deflections. Conversely, when you are far from the VOR, you must notice and react to rather small CDI deflections.

14.4.2  Approaching the Station

Just because the CDI has super-high sensitivity near the VOR doesn’t mean you have to pay super-close attention to it.

By the time you are within a couple of miles of the VOR, you should know how much wind correction is needed. The wind doesn’t change at the station! You should know the course to the station, so you should be able to get there (plus or minus a tenth of a mile) by dead reckoning. Therefore take up the correct heading and just hold it. Don’t chase the needle. Look outside.

The wind doesn’t change at the station.
     

14.4.3  Progress Along the Course

It is worth repeating what was said in section 14.2.2: When looking for a waypoint, such as your destination airport, it doesn’t do you much good to be on course if you have already inadvertently passed the waypoint. Therefore, it is vital to know how far you have progressed along the course. This is just as important as staying on course.

1) You can use distance/time/airspeed to keep track of your progress, as discussed in section 14.2.2.

2) You can also use pilotage: identify landmarks along the course, and put checkmarks on your chart as you pass each one.

3) GPS, LORAN, or DME make it easy to keep track of your progress along the course. VOR and NDB stations, provided they are not directly behind or ahead of you, can also provide progress information. To make use of this information, draw on your map. The navigation receiver will tell you what radial you’re on ... then draw the appropriate radial line from the station. The place where that line crosses your course-line is your present position. Another option is to pre-tune the OBS to the radial that corresponds to a point of interest ... when the needle centers, you’re there.

The question arises as to how far off your course the off-course station should be. If the station is too far away, you may have trouble receiving the signal. Also, the farther the station is away, the less precise will be the information you get from it, just because the same number of degrees will correspond to a longer distance. On the other hand, you don’t want the station to be too close to the course. This is because you want the cross radials to cross the course at a reasonably large angle (preferably 45 degrees or more); otherwise accuracy is impaired. Therefore, if you chose a station that is farther from the course its usefulness will extend over a longer portion of the flight.

14.4.4  Twisted VORs

In the region where I usually fly, every VOR is misaligned by several degrees. If you want to fly along an airway that is defined by, say, the 224 radial of a certain VOR, you need to hold a 227 heading in no-wind conditions.

Here’s why: In general, the radio-beams that a VOR radiates are not necessarily aligned with the actual magnetic directions. Presumably the transmitters were properly aligned when they were first installed, but some of them have not been re-aligned in over 35 years.

That’s significant, because the earth’s magnetic field changes over time. A VOR that was aligned with the magnetic directions several decades ago may disagree with the current magnetic directions by quite a bit. The FAA is “supposed” to re-align them, but they’ve fallen rather far behind. Re-alignment is a lot of work: not only do you need a really big wrench to rotate the transmitter, but you need to revise all the navigation charts.

Your GPS will agree with your compass and disagree with the VOR. That’s because GPS receivers have a database that can be updated with the latest map of magnetic variation.

Here are some of the implications:

Here is how you can ascertain the VOR twist: The first step is to obtain the actual magnetic variation in your area. Often the easiest way is to look through the Airport/Facility Directory13 and find a nearby airport that has been recently surveyed. That will give you the local variation as of a specified date. (Sectional Aeronautical Charts are another source of information about magnetic variation, but you never know how up-to-date that information is.) Also, your GPS may have a mode that tells you the local variation.14 The second step is to look up the VOR in the A/FD, and see what variation the VOR is aligned to. Subtract the VOR alignment number from the actual variation.

14.5  Combined Techniques

You should not hesitate to combine pilotage, dead reckoning, and navigation by instruments. For instance, you could use a VOR signal to stay on course left/right, and use time and groundspeed to measure you progress along the course. Conversely, you could use dead reckoning to stay on course and use a cross-radial to measure your progress along the course.

The combination of dead reckoning with pilotage is quite powerful. Dead reckoning helps you find your landmarks. Pilotage allows you to establish your position with certainty, so that small dead reckoning errors (which are inevitable) do not accumulate.

Also remember that navigation is not your only task. You still need to fly the airplane, watch for traffic, et cetera. You should run an enroute checklist every few minutes, as discussed in section 21.6.

14.6  Staying Un-Lost

Here are some suggestions to help you keep from getting lost:

  1. Keep track of your current position. I know this involves a certain amount of work, but remember: Staying un-lost is easier than getting un-lost. Consider the analogy: don’t wait until you have cavities and then start brushing your teeth. By the same token, don’t wait until you are lost to start keeping track of your position.
  2. Write on the charts. When you pass a checkpoint, write the time on the chart, so later you will know how long it has been since you were there.
  3. Choose unambiguous checkpoints. If you think you are heading for Jonesville, make sure you are not heading for Smithville instead. (A water tower with the word “Smithville” in twenty-foot-high letters should make you suspicious.) If your checkpoint is a round lake, make sure there is not another round lake a few miles away.
  4. Keep your DG aligned with the magnetic compass. Sometimes a DG will behave nicely for hours or even years. Then, just when you have become complacent, it will start precessing like crazy. Also note that radical maneuvering (steep turns, stalls, takeoffs and landings) can cause an otherwise well-behaved DG to lose a few degrees.
  5. Identify the Morse code on each navaid that you use. I’ve seen lots of students tune up the wrong navaid, or an inoperative navaid, and then blissfully follow the needle. Don’t just check that there is “some” Morse code, make sure it is the right Morse code.
  6. Make the VOR status flag part of your scan. If you lose the signal from the VOR (perhaps because you flew out of range, or perhaps because of a loose connection in your receiver) the CDI needle will settle in the center, making it look like you are doing an excellent navigation job no matter how far off course you are. The easiest defense is to notice that the “To / OFF / From” flag is showing “OFF”.
  7. Make a habit of getting enroute radar advisories (also known as flight following) from ATC. On my very first cross-country trip after getting my private pilot certificate, I was blissfully following road “A” when I thought I was following road “B”. Unfortunately, road “A” was leading right into the middle of a restricted area that was being used for air-to-air missile testing. Fortunately, I was getting advisories. A few miles before the restricted area ATC called me and suggested I make an immediate 90 degree turn. At that point I didn’t even realize I was lost, so it took me a while to understand what ATC was saying. Eventually I took the hint and everything worked out OK.

14.7  Getting Un-Lost

14.7.1  Basics

First of all, don’t panic. Being slightly lost is usually not, by itself, a big-time emergency. However:

14.7.2  When in Doubt, Climb

Low altitude causes lots of problems, including:

There are of course exceptions: For instance, you don’t want to climb into a cloud layer unless you have current instrument-flying skills and a clearance. Similarly, you don’t want to climb into restricted airspace without permission. Still, given the choice between running into a mountain and violating restricted airspace, the latter is preferable.

14.7.3  GPS or LORAN

Most GPS and LORAN receivers have a really nice feature: By pushing a button or two, you can display the name of the nearest airport(s), along with the bearing and distance from your present position to there.

These instruments will also, of course, tell you your latitude and longitude, but usually this is less convenient than the “nearest airport” feature.

14.7.4  VOR Cross Radials or VOR/DME

If you know even approximately where you are (within a few dozen miles), pick a VOR in the area and tune it up. Draw a line on the chart, along the radial that the VOR is telling you. Then pick a second VOR and draw another line. The point where the lines intersect is your position. If the lines cross at a shallow angle, the precision of the fix will be poor, so when picking the second VOR try to pick one that is well off the line given by the first VOR.

Of course, if you have VOR and DME, the job is even easier.

14.7.5  Ask ATC

Here is an exchange I heard on the radio, back when I was a student pilot:

Voice 1: PSA 1705, cleared for visual approach.

Voice 2: Approach, PSA 1705 is unfamiliar with the area, requesting vectors to final.

Voice 1: Roger, PSA 1705, fly heading 350, vectors to final.

I smiled when I heard that. I figured if airline captains could ask for vectors, so could private pilots, and even students.

It’s true: you don’t need to declare an emergency. You don’t need to admit that you’re lost. You don’t even need to be lost. You can just be slightly unfamiliar with the area.

ATC has radars. They can find you real fast, and give you a vector toward wherever you want to go. Even without radar, some flight service stations can find you by doing “direction finding” on your VHF radio transmissions (although this system is slowly dying of neglect).

Don’t worry about getting “blamed” for being lost. ATC would much rather have a lost pilot who is talking to them than a lost pilot who isn’t talking. You should be embarrassed enough to be motivated to do better navigation next time, but not so embarrassed that you hesitate to ask for help this time.

To contact ATC, if there is any doubt15 about what frequency to use, call up on 121.5 MHz. Practically every ATC facility can receive and transmit on that frequency. Yes, it is the “emergency” frequency, but it is not so special that you should be the least bit hesitant about using it.

14.8  Flight Planning

Here is a rundown of various flight-planning methods:

  1. The dead reckoning methods outlined here — even though they involve various approximations — are good enough for most purposes.
  2. One very good method is DUAT (Direct User Access Terminal). Its original purpose was to allow pilots to get weather briefing information on-line, but the contractor that provides the service has augmented it with a free flight planner. It will find a route for you automatically, then compute the courses, distances, headings, and times between waypoints. It gets the forecast winds aloft directly from the FAA weather computers. An important advantage of this approach is that you can, with very little effort, try several different routes and several different altitudes. Sometimes it’s worth going a little out of your way to pick up a tailwind. Information about DUAT in general and the flight planning features in particular can be found at the DUAT provider’s web site.
  3. On those rare occasions when I can’t connect to DUAT, I have a spreadsheet in my laptop that will calculate headings, times, fuel consumption, et cetera, given courses, distances, winds aloft, et cetera. You can download a copy of the spreadsheet (and instructions) from my web site, as discussed in section 23.2. If you are curious about the details of how to compute wind triangles to high accuracy, you can reverse-engineer the formulas in the spreadsheet.
  4. There exists a clever mechanical device called an E6-B which works like a slide rule for adding and subtracting vectors. I haven’t used mine in years. When I’m in the airplane, I use the rules of thumb discussed above to estimate headwind components and crosswind components. When I’m not in the airplane, I use a computer.

It is important to be able to solve navigation problems while you are flying the airplane. When you are in the cockpit improvising a flight plan, an approximate solution right now is vastly preferable to an exact solution that would require many minutes of careful calculation. There are many reasons why you might want to (or need to) improvise a deviation from your preconceived flight plan. These include:

Almost the only time you need really accurate dead reckoning is when you are taking FAA written tests. You will be allowed to use and E6-B or an “approved” electronic equivalent; a laptop will not usually be allowed. The tests sometimes contain questions where the right answer differs from the wrong answer by a tiny amount. In such cases, you must use the FAA-approved approximations16 and no others.

On a real trip (as opposed to a written test), if you are planning to rely on highly accurate dead reckoning, such as flying to the Azores without a GPS, then you should probably have your head examined.

As soon as you know your route, draw a line on your chart representing this route. Run your eyes along this line to make sure it doesn’t come too close to any obstructions or special-use airspace. At the same time, look at the “sector altitudes” for each box that your course line crosses. If your enroute altitude is above these altitudes, you are assured you won’t hit any terrain enroute. If you plan on flying below these altitudes, perhaps because you are flying through a mountain pass, you need to do a whole lot of additional work to select a safe altitude.

Make a column on your flight plan in which you note the minimum safe altitude for each leg.

The sector altitudes on the VFR chart offer very little safety margin. The ones on the IFR chart have much greater safety margins, horizontally and vertically. They are particularly useful for planning off-airways IFR flights ... but I like to use them for VFR planning, too, just because it’s an easy way to get a known amount of safety margin. See section 21.4 for additional discussion of obstacle clearance and decisionmaking.

There are of course many cases where it makes sense to fly below the sector altitudes, for instance if you have lateral separation from tall towers or mountain peaks. The point is that above the sector altitude, flight-planning is easy, whereas below the sector altitude the planning is much more intricate and laborious.


1
... presumably as a way of discouraging uninvited guests. The legend of the VFR sectional chart claims all recognizable hard-surfaced runways are depicted, but it’s not true.
2
The idea is that the direction from your thumb to finger is the same before and after the move. You may want to practice this skill. Here’s a good exercise: find a nice straight Victor airway on the chart. Put your thumb and forefinger on it, twenty or thirty miles apart. Then move your hand to a compass rose that is not on the airway, and read off the heading. Finally, look back at the airway and see what the “official” heading of the airway is. With a few minutes practice, you should be able to get within a couple of degrees.
3
See section 14.3.2 for a list of navigation systems and their acronyms.
4
In many airplanes, there is a device like a circular slide rule built into the airspeed indicator that allows you to calculate the true airspeed, given the indicated airspeed, altitude, and temperature. Otherwise, you could perhaps use your E-6B. Typically though, it suffices to use the simple rule: two percent per thousand feet.
5
That’s how nautical miles were originally defined, and that’s why aviators use them. A nautical mile is about 1.15 statute miles, or about 1.85 kilometers. A knot is defined to be a nautical mile per hour.
6
To practice these techniques on the ground, you can use the compass roses on the chart, in the same way that you would use the DG if you were in the airplane. That is, draw a line from the edge of the compass rose to the center, representing the total wind, and then resolve it into components parallel and perpendicular to your course line.
7
You don’t need to memorize the table. You just need to remember that there are about 57 degrees in a radian; then you can figure out the rest at a moment’s notice. The figuring is even easier of you approximate π by 3.0 (i.e. 60 degrees per radian). You can speed things up by remembering the conversion factor (degrees per knot of crosswind) that applies at the typical groundspeed of your airplane. Also, you can usually simplify the calculation by comparing the crosswind component to your airspeed (as opposed to groundspeed), unless the headwind or tailwind component is really large.
8
To calculate a more-accurate course, see section 14.4.4.
9
If you want to get technical about it, you should recalculate the crosswind component after correcting for the crosswind, but you will find that this is almost never a significant correction.
10
... enroute navigation, that is. In contrast, if you are performing an instrument approach, you might want to do better, but that is a different subject.
11
If you forget to account for twist, you can drive yourself crazy trying to figure out the winds aloft. Suppose you are following a north/south airway that is twisted by +3 degrees, flying at 120 knots in no-wind conditions. Then your instruments will seemingly indicate 6 knots of “wind” from the east when you are northbound on the airway, and seemingly indicate 6 knots of “wind” from the west when you are southbound on the same airway!
12
This is the most accurate check you can do, but does not quite meet the requirements for the mandatory 30-day receiver check — unless you check two VOR receivers at the same time and sign it off as a cross-check.
13
The A/FD is published as a small book every 56 days. The same information is also available on the web, which is often more practical. For example, search for “JFK VOR variation”.
14
Every GPS has a database of detailed information about variation as a function of location. It needs this so it can calculate your magnetic course based on a sequence of positions.
15
At the other extreme: if you are already talking to ATC on a given frequency, you should undoubtedly use that frequency.
16
In particular, the test-makers apparently believe π = 3 (i.e. 60 degrees per radian). I remember one question where you would be marked wrong if you used π = 3.14 (i.e. 57 degrees per radian).

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