Alexander Burton, CFI

Pacific Rim Aviation Academy Inc.

Pitt Meadows Regional Airport

393-11465 Baynes Road

Pitt Meadows, BC V3Y 2B4

-Tennessee Williams-

Tom Robbins suggested in one of his novels that water invented life as a means of

carrying itself about the planet. Whether or no, time and distance are two of the factors

we face in aviation each and every time we take to the skies. They are, to a large extent,

defining factors for much of what we do and are the basis for many of the important

decisions we must make as pilots.

One of the critical questions we must ask and answer every time we make the decision to

fly is how long can I remain in the air and how far can I travel in this particular aircraft

under the existing conditions with the fuel load I have on board. It is also important to be

able to evaluate where we are in relation to specific points both for navigational purposes

and for position reporting.

More and more GA aircraft are being equipped with GPS and other modern devices that

take some of the burden away from pilots. Decisions and judgements, however, must still

be made and there are a couple of simple techniques that can be easily incorporated into

our repertoire to help us along the way.

One of the most basic skills, very helpful to a pilot, is learning how to judge how far

away and what direction something is by looking at it. It sounds simple enough, but it

does take some time, work and energy to master. Judging from some of the whimsical

position reports I hear on a regular basis, it is not a skill that has been well learned by

many pilots.

As with any skill, practice is the key to success. Start in a familiar area. Take out your

map, orient it so what you are seeing outside is the same as what you are seeing inside,

and identify as specifically as possible your position. Note prominent features nearby and

their positions in relation to your aircraft. Pick one to start with and estimate its distance

and the heading from it to you. Confirm the distance and heading using your map. Now,

pick another.

If your aircraft is equipped with a heading indicator, this can be a big help in determining

the direction of your position from a given reference point. Imagine for a moment your

heading indicator lies flat in your lap instead of on the panel. If you are heading North

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and the reference point you are observing is sixty degree to your right, on a heading of

sixty degrees from you to it, you are located South-West of the reference. If you are

heading West and the reference lies, say, sixty degrees to your left, your position is

North-East of the reference. Solve the problem visually. No math required.

The more you practice, the more accurately you will be able to estimate distances and

headings just by looking. Make a habit of practicing each time you are up flying to keep

the skill sharp.

What does three miles actually look like? How about 30 miles? If a given point is south

of me, I am north of it.

ATC does not seem to appreciate you reporting ten miles south of the airport when, in

fact, you are three miles east and already well inside the control zone. Other pilots

appreciate an accurate report of your position so they know where to look for you.

Making quick and easy estimates of flying time from one point to another is also a very

useful skill. Of course, your GPS will give you a very accurate estimate, but there are

times when the old system of ground, watch and map can do the job just about as well

and at a fraction of the cost, and, GPS’s have been know to fail, usually just when you

need them most.

Many people—I see this regularly on flight tests—get stuck with the concept of

measuring distance and then attempting to convert that into time based on airspeed or,

more accurately, ground speed. This is all well and good if you are sitting peacefully at

your desk in good light and have a calculator or E6B handy with which to complete the

calculations. It’s another matter sitting in a moving aircraft. And, we all know that the

more difficult it is to do something the less likely we are to do it.

We have all experienced our IQ drop at least 50 points the moment the wheels leave the

ground. In a small aircraft bouncing about the sky, simple is good.

For a quick estimate of time from point to point, have a look at your airspeed indicator.

At 100 Knots, we will cover 10 NM every six minutes; at 80 Knots we will cover 8 NM

every 6 minutes (1). This does not take into account wind or the difference between

indicated airspeed, calibrated airspeed and true airspeed, but it is still pretty accurate with

slow moving GA aircraft, particularly if we make an additional progress check along the

way. We don’t need to be perfect, just good enough to do the job at hand.

Let’s say I take a quick look at my airspeed indicator and note I am flying at an indicated

airspeed of 100 Knots. I know each 6 minutes I will travel about 10 NM. I can use a

pencil or my fingers, reference the minutes of latitude on the vertical scale of my map

and determine a 10 NM length (2). I am not so much interested in the distance but rather

the flight time that distance represents.

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In flight, time is everything. Knowing how far away a given point is in miles, kilometres

or rods is not terribly important. The important information is how much time it will take

me to get there and how much fuel I will burn along the way, which is also a function of

time rather than distance. We measure fuel in gallons or litres per hour not in gallons or

litres per mile.

How far is it from Boundary Bay to Chilliwack? If I’m walking or riding my bike, it’s a

long way; if I’m flying at 90 Knots, it’s pretty close; if I’m flying at 300 Knots, it’s very

close.

Now, using our 10 NM length we can count out increments of 6 minutes from our

position to any other. Most of us have learned to count by 6’s, so it is a simple, geometric

problem: 6, 12, 18, 24 and so on. We don’t have to do any calculations, the end of many a

good pilot, while trying the fly the aircraft.

Knowing my time enroute, I can add that to my time over a given position and arrive at a

pretty accurate ETA. If it’s 35 minutes after the hour and it will take me 28 minutes to

arrive at my destination my ETA is 3 minutes after the coming hour (3).

If I want to verify my progress, I can record the time it takes me to fly from one known

point to another on the chart. I don’t have to worry about the measured distance; I just

need the time it takes to fly between two, identifiable points. This automatically takes

into account wind without any effort on my part since my answer is a direct measure of

time to fly a given distance under existing conditions.

Let’s say it takes me 8 minutes to fly between two, given points along my route. I can

take the distance between those two points, measured either with a pencil or my fingers,

and see how many more increments of that distance lie between my current position and

my destination. In this case, I just count by 8’s to derive my ETE. Five increments of that

distance tells me it will take 40 minutes under existing conditions.

If I make any significant heading changes along my route, it may be an excellent plan to

re-evaluate my ETE since wind may affect my speed over the ground differently on a

different heading.

I have used this method quite satisfactorily flying my little Citabria from Alberta to BC,

from BC down to California and return and all around the coastal area. I find, with a little

care to detail, my ETA estimates are never more than 1 or 2 minutes out, even over the

two to three hundred miles I fly between breaks. Good enough to do the job and probably

more accurate than they might be if I were to get lost in complex computations.

Keep it simple. Enjoy.

Notes:

1. 100 Knots = 100 NM/60 minutes; drop the 0’s and we have 10 NM/6minutes. This works for any speed:

at 130 Knots I travel 13 NM/6minutes; at 75 Knots I travel 7.5 NM/6 minutes.

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2. One nautical mile, 6,080 feet (more precisely 6,076.11549 feet) is one minute of arc of a great circle of

the Earth. The distance over the earth’s surface represented by the arc distance between minutes of

latitude or the arc distance measured between lines of longitude at the equator is equal to one nautical

mile.

3. This exact problem is why I always wear on old time analog watch. I try to avoid the math during flight

whenever possible. 35 + 28 is a bit ugly as a math problem, but if I look at my watch I can make the

calculation by simply looking at the watch face. I find 35 after the hour, half way around the dial is

adding 30 minutes, making it 5 after the coming hour and moving back the extra two minutes (30-28=2)

shows my ETA as 3 after the coming hour.