Tips for estimating distance?

livitup

livitup

Pre-takeoff checklist
Joined
Jul 16, 2009
Messages
357
Location
Southern Northern Virginia
Display Name
Display name:
livitup
I've never been good at estimating distance - if you ask me, for example, how long my driveway is, or how far it is from my front door to the neighbor's front door, my answer is likely to be off by a bunch.

I'm recognizing this might be an impediment to flying - I was just watching the first video in my ground school about ground reference maneuvers. On the topic of flying a rectangular pattern around a ground reference, they said "fly the pattern about 1 to 1.5 miles outside the reference." I started panicking before I even thought about making the turns and correcting for wind, because I have no earthly idea what 1 mile should look like, on the ground, or in the sky.

Anyone else have this problem and a tip or two for overcoming it?

I do realize I'll be able to recognize a 1 mile distance from the wing strut to the area I practice in, and line up in that same spot in order to do the maneuver, but the real concern I have is how to make that "measurement" in foreign territory? If the DPE says "do some rectangles around that corn field..." or even worse, "how far are we from that corn field" I'd rather have a better answer than :dunno:.
 
Most runways are about a mile long, use that as a gauge. You are used to seeing runways from different altitudes, so take a guess at how many runways are between you and whatever object.
 
It's pretty easy where I am, the section lines are all 1 mile square.

You'll get used to it. Look at things out the window, take a guess, then look at the sectional and see how you did.

PS - ground reference maneuvers will approximate what you do in the pattern, so you'll have a general feel for the distance.
 
Take a look at the runway at your home field. Check the A/FD for information on it's length.

A mile is a 5280 feet.

At KDTO, their runway is 7000 feet. So when I'm cleared in for a straight in approach, and they want me to call a 4 mile final, I take 3 runway lengths and project it toward me from the threshhold.

Use the same concept with your runway and you'll eventually get it.


A tip for the rectangles is to pretend the fence line is the centerline of the runway. If the instructor has you matching a particular spot on the strut with the runway center line, put that spot on the fence line. Make your turns where you should, and correct for wind as needed.

Your instructor will coach you about distance as needed.
 
If the runway is half a mile long, you can compare to the runway length as an estimate of how far you are away.

If you are at 5280 feet AGL, a point at a 45 degree angle is one mile away. I thihk. I don't normally fly that high.

Besides, based on the position reports I hear on the radio, many pilots totally suck at guessing where they are and what direction they are going.
 
Capt. Geoffrey Thorpe said:
If the runway is half a mile long, you can compare to the runway length as an estimate of how far you are away.

If you are at 5280 feet AGL, a point at a 45 degree angle is one mile away. I thihk. I don't normally fly that high.

Besides, based on the position reports I hear on the radio, many pilots totally suck at guessing where they are and what direction they are going.
Click to expand...

That point is the hypotenuse of your right triangle with legs of 1nm. The distance is slightly longer at 1.14...close enough to impress a government inspector
 
Jaybird180 said:
That point is the hypotenuse of your right triangle with legs of 1nm. The distance is slightly longer at 1.14...close enough to impress a government inspector
Click to expand...

Actually, shorter if you want nautical miles (.868) if you are at 1 statute mile AGL. I guess you would want to be at 6076 feet AGL for that trick to work in nautical miles. But, like I said, that's awful high to be flying an airplane.
 
Best tip: Take your best guess, and don't worry whether your correct.

(hint: your never going to be exactly right, but your best guess probably going to be close enough.)
 
dell30rb said:
Most runways are about a mile long, use that as a gauge. You are used to seeing runways from different altitudes, so take a guess at how many runways are between you and whatever object.
Click to expand...

There is a great deal of variation. The actual length is on your sectional (which you DO have, right?). 1/2 mile runways aren't THAT rare, and 2+ miles exist, even for light GA airports. And then there is my favorite at KEDW, which clocks in at 7 miles.
 
I think I posted this before, but in my 172, as objects disappear under the cowl, they are roughly as many miles away as I am AGL in thousands.

Example: I'm 4,000' AGL, the object going under the cowl is 4 miles ahead.

YMMV depending on your eye level in the airplane. (Your height, seat position, etc.) Try it in your plane with known landamarks/distances and see what you get.

Edit: Level flight is assumed.
 
Last edited:
dell30rb said:
Most runways are about a mile long, use that as a gauge. You are used to seeing runways from different altitudes, so take a guess at how many runways are between you and whatever object.
Click to expand...

"Most" isn't a good idea. One needs to know the exact length of ones reference distance. Airports are fine but, find the exact distance in the AFD, one a mile long if that's what you like.
 
The runway length is really useful for when Tower tells you to report on 2 mile base or whatever. Another situation is the first callup approaching a nontowered airport. A trick for that is that VOR roses are 5 mile radii on TACs, and 10 miles on sectionals. Pick a nearby landmark and gauge your distance from the field that way (this works even when approaching on the 45 like you're supposed to, when it's hard to see how long the runway is).
 
my CFI had a neat trick, he knew points along the wing strut that corresponded to various distances. Just take some known distances and see where they are on your strut, from your normal seating position.
... dang... my CT has no struts!
ps. There's a feature in WingX I love... position report... it gives you a position report in the lower-left corner. After using this for a while, it does a good job of teaching you distances.
 
Last edited:
Take a GPS, go up to 2500'AGL. Fly 2 miles, 5 miles, 10 miles from the airport. Know what this looks like. Climb to 5000' AGL, and note what it looks like from there. Do this for various distances, and altitudes.

Eventually you'll get close enough on your guesses.
 
Capt. Geoffrey Thorpe said:
Actually, shorter if you want nautical miles (.868) if you are at 1 statute mile AGL. I guess you would want to be at 6076 feet AGL for that trick to work in nautical miles. But, like I said, that's awful high to be flying an airplane.
Click to expand...

I learned in school that the hypotenuse of a right triangle is always a greater value than the length of the longest leg. Did I mis-learn?
 
Don't sweat it so much, there's a reason it's called an "estimate". You may feel intimidated but it's only over the past 10 years or so, since the advent and wide spread use of GPS, that people started calling their distance out to the nearest tenth of a mile. In reality they aren't any better at guessing than you are. Even in the old days when people would call out their DME distance it wasn't that accurate because DME is slant range.
 
Jaybird180 said:
I learned in school that the hypotenuse of a right triangle is always a greater value than the length of the longest leg. Did I mis-learn?
Click to expand...

a squared + b squared = c squared

where c is the hypotenuse

So yes the hypotenuse is the longest leg of a right triangle
 
Jaybird180 said:
I learned in school that the hypotenuse of a right triangle is always a greater value than the length of the longest leg. Did I mis-learn?
Click to expand...

No - you done lernt good. But if you report 1 mile away from the airport, that's one mile along the ground - right? At least that's what I always assumed.

The hypotenuse of a right triangle with equal legs is about 1.4 times each leg. So if you are one mile above the ground, look out at a 45 degree angle down, what you are looking at is 1.4 miles from your eyeball, but 1 mile away from your horizontal position along the base of the triangle.

So, if you are counting section lines then you are measuring the distance along the ground.

If you look at the number on the GPS I think it gives you the horizontal distance - the base of the triangle - when you pass over a point the distance should be 0 and not your altitude - right? Anyone got one of those that can check?

If you look at the number on a DME I think it gives you the hypotenuse - or am I wrong about that too?
 
Thanks for the support and the tips. My home airport is 5000 feet, so pretty close to a mile. I'll try and get a good sight picture of it at a few different altitudes the next time I have a chance.

It's reassuring to hear that it's something that comes with practice. I've never really tried to improve my mental measuring skills, so I was worried I'd never be able to figure it out.
 
That's why it's called an 'estimate'.

My experience, based on the guy that's doing some work on my house, is that an 'estimate' has quite a large margin of error.
 
BTW Whenever anyone asks you,"How far away is that cloud?", the answer is "At least 2,000 feet."
 
upstateny said:
BTW Whenever anyone asks you,"How far away is that cloud?", the answer is "At least 2,000 feet."
Click to expand...

I get the joke, but that's another really good example. How do you really estimate distance to a cloud... Now you don't even have ground references to misuse.
 
livitup said:
I get the joke, but that's another really good example. How do you really estimate distance to a cloud... Now you don't even have ground references to misuse.
Click to expand...

You can't. That's part of the joke. To estimate distance, you need to know size, and you don't for a cloud.

Some pilots think they can measure distance from a single perspective. Ask anyone who has tried to avoid a collision with Venus (and don't laugh TOO hard -- that sucker is by far the brightest thing in the night sky behind the moon, and looks a heck of a lot like a landing light coming right at you when it's low on the horizon).
 
livitup said:
I get the joke, but that's another really good example. How do you really estimate distance to a cloud... Now you don't even have ground references to misuse.
Click to expand...

There is a secret PoA calibration tool for determining whether you are far enough away from a cloud or if a hole is big enough to fit through.
 
Near a runway, I usually know its length, so that helps. But otherwise, if I really want to know, the chart comes in handy there.

As for traffic and clouds ... it's an art, I guess. Cloud shadows (or a line visualized from the edge straight to the surface) can be used along with the chart, but the rest is guesswork, but most pilots get better at it as they go along. It helps to be in the habit of using your nav tools to find distances to visual landmarks, just for practice.
 
Jaybird180 said:
Ok, I'll bite
Click to expand...

We were at a fly-in and waiting to see if the ceilings were going to lift or if there was going to be a hole that opened up for the VFR people to get out. One of the attendees (no, it wasn't me) just pipes up and dead pans...

"I always wondered how to tell if a hole in the clouds was big enough to get through VFR, and then I just figured if [PoA Member]'s head could fit through it I'm good."

You're welcome to guess who they were referring to. I'm sure I could give you three guesses, and you wouldn't need two of them. And no they weren't talking about the physical size of their head.
 
Here in Ponderosa Pine tree country, I find a quick outstretched arm and aiming my thumb towards a mature pine tree works well. If the tree is as wide as my thumb, then it is approximately 500 ft away. Half as wide, 1000 ft. 1/4 as wide, 2000 ft.

You will need to calibrate your own distance because arm lengths and thumb widths vary among POA members, and you may need a common reference other than Pine trees. :wink2:

For estimating distance below clouds, you can pick a cloud point that is 45 deg above your horizon, and then time how long it takes for that point to go directly above you. If your airspeed is 120 kts, then if it takes more than 2.5 seconds to go from 45 deg to 90 deg up, then you are 500 ft or more below the clouds. At 150 kts, anything greater than 2 seconds = more than 500 ft below.
 
I can only think of 2 distances that actually matter:
1. Am I close enough to make it?
2. Am I high enough to make it?
(related to #2: "Is the fall going to kill me?")

Everything else is puffery.

:D
 
don't feel bad. I"m awful, too. Things that don't have a set size, i.e. clouds, tree lines, etc are difficult for me to estimate as far as distance.
 
Judging distances come with practice. If ATC asks you to call 3 mile final, if you're 4 miles, most times they won't jump down your throat. For patterns, I position the runway about 1/2 way along the wing and gets about a mile. For a C172, I go half way up the wing support.
Practice calling distances with your instructor. It doesn't have to be an airport. Roads, lakes, buildings all work.
And remember, even after you pass your checkride, you'll still be wondering what the distances are.
Only practice gets you to Carnege Hall. Same deal here.
 
Why not just use a GPS? It is laser accurate. When you are flying around input the airport into the GPS. It will give you exact distance to the center of the airport. Estimating comes with practice.
 
Geico266 said:
Why not just use a GPS? It is laser accurate. When you are flying around input the airport into the GPS. It will give you exact distance to the center of the airport. Estimating comes with practice.
Click to expand...

Except when it doesn't.

Handhelds and especially smartphones and tablets can be really, really bad, without warning.

I had one tell me I was 20 miles south of my actual position on Saturday, all the way on the other side of Class B from where I really was. I'd be defending my certificate right now if I had depended upon that; it said I was short of Class B, when I had actually transited all the way through it (with clearance, but you usually have to know to ask for that).

Panel-mounts are better, but they don't always work either (generally, they DO tell you when they aren't working; they must if they are IFR approved).

One must never depend upon a gadget. They are fine for supplementary information, but you simply must be able to judge rough distances and directions as well as your position with a dead battery in your handheld or a complete power failure.

The correct answer is to use the runway length as a ruler. Get your eyes OUTSIDE THE AIRCRAFT in or near the pattern, as much as possible. Heads down playing with your iPad is dangerous.
 
Last edited:
You must log in or register to reply here.
Back
Top