Estimating distance

jstro

jstro

Pre-takeoff checklist
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Jan 2, 2010
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Northeastern IL
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Display name:
John S
An area of uncertainty to me is estimating distance, especially when approaching an airport. For example, if the tower at an unfamiliar airport tells me to call a 2 mi left base, I'm just really not sure what 2 miles looks like (as opposed to 1.5 miles or 3 miles). I suppose this is probably a matter of experience, but as a relatively inexperienced pilot, are there any tricks to help? I was reading a NTSB report of a MAC at my home airport (Class D, no radar at the time) which was partially due to one pilot consistently misreporting his position by a mile or sometimes more.

One thing I've done is used Google Earth to float around at pattern altitude and see what the airport looks like from certain distances, which I think does help.
 
jstro said:
An area of uncertainty to me is estimating distance, especially when approaching an airport. For example, if the tower at an unfamiliar airport tells me to call a 2 mi left base, I'm just really not sure what 2 miles looks like (as opposed to 1.5 miles or 3 miles). I suppose this is probably a matter of experience, but as a relatively inexperienced pilot, are there any tricks to help? I was reading a NTSB report of a MAC at my home airport (Class D, no radar at the time) which was partially due to one pilot consistently misreporting his position by a mile or sometimes more.

One thing I've done is used Google Earth to float around at pattern altitude and see what the airport looks like from certain distances, which I think does help.
Click to expand...

The first thing you can do is get a decent road or topo map that shows your home airport (an aero. chart may not show enough detail). Note the landmarks at 1 mile, 2 miles, etc., and look for them when you're leaving/approaching the pattern. That helped me a little... I even started by plotting a normal 1/2-mile pattern on a road map, then going up to see if I was really flying that pattern when using the "halfway up the strut at 1000 AGL" method (turns out I was pretty close).
Beyond that, the only aid, beyond simple repetition, is to make a habit of using the chart (or GPS) to determine your distance from any given landmark, and just noting what the angle, etc. looks like from that altitude. Then you can play a game in cruise: as you scan, pick out something, try to guess how far away it is, then check your estimate against the chart. This is also a good way to quickly determine what the visibility is at any given point, for those moments when you are not sure if it's within limits or not.
I still find judging distance to be tricky sometimes, but these little exercises help, for sure.

Bear in mind: I am NOT recommending you be heads-down, looking at chart or GPS, while within 5 miles of an airport, to try to be accurate with your position reports. No matter how accurate your reports are, the radio will not save you from a midair- only your eyes can do that.
BUT:
As you descend from cruise to land at some new field, or even before you take off on your flight, look at the local area around the destination on the chart for a moment. Decide beforehand where you will call 10 miles (if so inclinded), where you will call 5 miles, etc.
 
The easiest thing to do, especially around the midwest, is look at farm fields. Each field is usually a mile. I'm not sure where your airport may be, relative to farm fields, but in IL you can't be too far. Go out over some farms at roughly pattern altitude and a get a feel for the sight picture of two miles. Or go to a towered airport with RADAR and ask them to tell you when you're two miles out. Just be aware of potential optical illusions from runways of differing sizes. Or get on Google Earth again and find some identifiable point on the ground (a street, water tower, distinct building, etc) that's two miles from the runway and start to build your sight picture from that.

Bottom line, don't worry too much about it. They know you don't have DME, and thus won't be spot-on at two miles. Reports like that are usually just so that they tower controller can know where to start looking for you. In my limited experience, most non-radar towers these days seem to have a BRITE (radar feed from approach/center) so they'll call you in sight even before you get to the reporting point.

By the way, welcome to POA!
 
Another handy reference for distance is the runway itself. Theoretically you should already know how long the runways are at any airport you intend to land at and you can use that as a yardstick to estimate other distances when you are close enough to identify the runway ends. A 3000 ft runway is almost exactly half a nautical mile, a 2600 ft runway is half a statute mile.

Also you must understand the reason you are asked to report a certain distance from the airport. It's simply to give the tower a heads up that you've gotten close enough that they should be able to spot you (sometimes using binoc's) and fit you into the immediate flow. Even if the tower has a remote radar display it's a lot easier for them if they don't heve to keep track of all the planes that are outside the pattern. The take away on this is that there's no need to worry about being off half a mile or more when you report in, it will still work out fine and nobody is out there checking on your measurements. IOW, if you make the two mile call at three miles it won't matter but if you wait until you're already in the pattern to call you could have done better. The main thing is to not forget to call and to be accurate with your direction from the airport on your first call. A lot of pilots mess that part up pretty good (hint: read your direction from the bottom of your DG before making the initial call if you have one).

Incidentally, I think the accuracy of your position reporting is more important at uncontrolled fields (especially when close in) because in that case there will be two errors, yours and the estimate of your location made by anyone else in the vicinity. And the same techniques apply: charts, section lines, runway ruler.
 
Teller1900 said:
The easiest thing to do, especially around the midwest, is look at farm fields. Each field is usually a mile.
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He lives not too far from me and I was going to recommend that very technique. Flying in the Midwest it is easy to judge distance and direction too. Since most of the roads are North/South or East/West you also have a pretty good idea of which direction to head.
 
It's just a ruff idea for others. When I call in I say I'm about x miles out. By the time they hear you, find you, you'll be 2 miles down the road. It is just to alert people of where your at. Relax and call it how ya see it. Be more detailed when it's busy. Enjoy the view and don't stress.:thumbsup: Just dont' get your directions wrong, different story imho. :D
 
gismo said:
Another handy reference for distance is the runway itself. Theoretically you should already know how long the runways are at any airport you intend to land at and you can use that as a yardstick to estimate other distances when you are close enough to identify the runway ends. A 3000 ft runway is almost exactly half a nautical mile, a 2600 ft runway is half a statute mile.
.
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:thumbsup: +1. That's the one I teach and use the most since it works over almost any terrain.
 
If you can estimate angles, that can be useful. You know your altitude. If you look down at a 30 degree angle from the horizontal, your gaze meets the ground at distance twice your altitude. At 45 degrees, your gaze meets the ground at a distance equal to your altitude. Also, I second using the runway length as a standard.
 
Welcome to the POA world! I agree with everything said so far..also you can use your chart beforehand to see the outline of the class D airspace around the field note the circumference of the airspace and apply it to the landmarks you can see from the air. Its mainly a matter of practice and familiarity. And if you are ever not sure and have a transponder aboard, ask the controller to let you know how far out you are from the field at a given point in time and use that info to paint a sight picture of distance and landmarks...its the old use whatever resources are available to you thing.
 
Thanks to everyone who has responded! You're advice is helpful and much appreciated.
 
jstro said:
An area of uncertainty to me is estimating distance, especially when approaching an airport. For example, if the tower at an unfamiliar airport tells me to call a 2 mi left base, I'm just really not sure what 2 miles looks like (as opposed to 1.5 miles or 3 miles). I suppose this is probably a matter of experience, but as a relatively inexperienced pilot, are there any tricks to help? I was reading a NTSB report of a MAC at my home airport (Class D, no radar at the time) which was partially due to one pilot consistently misreporting his position by a mile or sometimes more.

One thing I've done is used Google Earth to float around at pattern altitude and see what the airport looks like from certain distances, which I think does help.
Click to expand...

I had a problem with that from my primary lessons and blame the instructor for lack of guidance. I didn't figure it out until I started flying with planes that had GPS and could get that sight picture in my head. To me, it is darn close to the airport from traffic pattern altitude (~1,000 AGL). Sight picture was a little off the nose of the plane.

Put it another way, do you have an estimate how far out from the runway you are when you are flying the downwind for a landing? If that is one half mile out, then the 2 mile out is four times that distance.

Please use a sight picture and don't just remember local ground points for your local airport since you won't have those when you go cross country.

S. Morgan
 
gismo said:
Another handy reference for distance is the runway itself. Theoretically you should already know how long the runways are at any airport you intend to land at and you can use that as a yardstick to estimate other distances when you are close enough to identify the runway ends. A 3000 ft runway is almost exactly half a nautical mile, a 2600 ft runway is half a statute mile.
Click to expand...
This is by far the easiest method, and the one I use and teach to all my students, and if your flying at big airports, the big runway is usually 2 milles (10K feet) so you can use that as a reference. Another good method is the slant range method, it varies from aircraft to aircraft, but a good rule of thumb is that the altitude in 1000s of feet will be equivalent to the number of miles when the surface is just visible over the nose cowling. In other words if your at 1000 ft and in level cruise flight at a constant airspeed the ground just visible at the cowling edge is 1 mile away. 2000' it is two miles, etc. Really good method for estimating visibility in marginal conditions. The way to calculate for cutoff angle for your aircraft is to sit in the seat and have someone measure from your head to the ground, then from that spot on the ground to a point out ahead of the aircraft where you can just see over the cowling, then divide the two numbers to get the tangent, Example 6' eye height and 30' distance is 6/30=.20 .2 is the tangent therefore angle would be roughly 11.5* and the approx vis at 1000' would be 5000' or 1 mile (roughly).
In Sparky Imeson's "Mountain Flying" book there is a chart denoting cockpit cutoff angles and flight visibility, really a great book.
 
If they ask you for a distance, it is best to try to give it, but if there is a familiar or prominent landmark, that can also help. Yes, there may be two football stadiums or two interstates, so don't choose one willy nilly. Use something unique, readily known, easily identified and so forth. You'll note that some towers ask for a report "over the XYZ bridge" or some such.
 
I believe most people use the GPS distance to say how far out they are. Now when the controller asks for a report 3 miles out on final, that distance may be up to a mile off if you are at a very big airport. So the question is what should our reference be? Looks like it depends.
 
Pegasus said:
I believe most people use the GPS distance to say how far out they are. Now when the controller asks for a report 3 miles out on final, that distance may be up to a mile off if you are at a very big airport. So the question is what should our reference be? Looks like it depends.
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It really doesn't matter. The purpose of a 3 mile report is to help the controller pick you up visually and also serves as a wake up call for them to work you into the flow before you get into the pattern. If you make that call at 3 miles from the center of the airport, 3 miles from the tower, 3 miles from the closest corner of the field, or anywhere between 2-4 miles from any point on the field it will work out.
 
Pegasus said:
I believe most people use the GPS distance to say how far out they are. Now when the controller asks for a report 3 miles out on final, that distance may be up to a mile off if you are at a very big airport. So the question is what should our reference be? Looks like it depends.
Click to expand...

I've generally always avoided towered airports, but when I have decided to enter Class Cs or Ds to land, I've never heard "report 3 miles on final", even when given a straight-in. I've always been given a landmark at which to report.
At KSDM, it's either the prison east of the field or the highway to the west. At KNEW, it was a fish hatchery on the lake east of the field. Arriving at KCNO in a Champ without a transponder, they asked me to report abeam the tower on downwind.
At KTEB, where I've made most of my tower-controlled takeoffs and landings, I don't recall ever getting a request to report at a given distance or at a landmark, unless they wanted to confirm where I was at any given moment.

Visual landmarks, even if one is not from the area, work very reliably... especially if one does not have GPS (I didn't have one for any of those flights).
 
rottydaddy said:
I've generally always avoided towered airports, but when I have decided to enter Class Cs or Ds to land, I've never heard "report 3 miles on final", even when given a straight-in. I've always been given a landmark at which to report.
At KSDM, it's either the prison east of the field or the highway to the west. At KNEW, it was a fish hatchery on the lake east of the field. Arriving at KCNO in a Champ without a transponder, they asked me to report abeam the tower on downwind.
At KTEB, where I've made most of my tower-controlled takeoffs and landings, I don't recall ever getting a request to report at a given distance or at a landmark, unless they wanted to confirm where I was at any given moment.

Visual landmarks, even if one is not from the area, work very reliably... especially if one does not have GPS (I didn't have one for any of those flights).
Click to expand...
You live a sheltered life.
 
rottydaddy said:
I've generally always avoided towered airports, but when I have decided to enter Class Cs or Ds to land, I've never heard "report 3 miles on final", even when given a straight-in. I've always been given a landmark at which to report.
At KSDM, it's either the prison east of the field or the highway to the west. At KNEW, it was a fish hatchery on the lake east of the field. Arriving at KCNO in a Champ without a transponder, they asked me to report abeam the tower on downwind.
At KTEB, where I've made most of my tower-controlled takeoffs and landings, I don't recall ever getting a request to report at a given distance or at a landmark, unless they wanted to confirm where I was at any given moment.

Visual landmarks, even if one is not from the area, work very reliably... especially if one does not have GPS (I didn't have one for any of those flights).
Click to expand...
Plenty of Class D and C towers will tell you to report a distance. I've had more tell me to report a distance then I have had a landmark. Maybe it's a midwest thing.

I'll report landmarks if they ask and I'm *very* familiar with the area or the landmark is obvious, like a major river. Else I just decline and tell them I'm not familiar with the landmark.
 
Easiest thing to do is buy a decent GPS. Flame away, but with the situational awareness you get for the money the things are a total bargain.
 
jesse said:
Plenty of Class D and C towers will tell you to report a distance. I've had more tell me to report a distance then I have had a landmark. Maybe it's a midwest thing.
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Well, it is sorta difficult to use a farm field as a reporting point in many midwest states...and there might not be any other "landmarks" around.:smile:

BJC used to use the Storage Tek campus as a reporting point. Sorta-gotta be a local to get that one. APA still uses Cherry Creek reservoir but at least that's the big pond north of the runways so just about anyone can figure it out eventually. I do hate it when they say "Report Parker Road" 'cause that's just another four or six lane running southeast and the airspace is usually just a bit busy for me to be wasting time figuring out if this road or that road is Parker. For some reason I just can't read the street signs from 1,500 agl.
 
Clark1961 said:
Well, it is sorta difficult to use a farm field as a reporting point in many midwest states...and there might not be any other "landmarks" around.:smile:

BJC used to use the Storage Tek campus as a reporting point. Sorta-gotta be a local to get that one. APA still uses Cherry Creek reservoir but at least that's the big pond north of the runways so just about anyone can figure it out eventually. I do hate it when they say "Report Parker Road" 'cause that's just another four or six lane running southeast and the airspace is usually just a bit busy for me to be wasting time figuring out if this road or that road is Parker. For some reason I just can't read the street signs from 1,500 agl.
Click to expand...

They used to use landmarks around here but I haven't heard one used by the tower in several years. Probably because they were getting mis-reported as often as not and they only work for the locals and the three non-local pilots who actually had an area chart showing the designated VFR landmarks unfolded and knew how to use it.

We have plenty of landmarks but most are easily confused with others. I happen to know most of the names for the lakes in the area but found that most pilots and some controllers had no idea which lake was which other than the two adjacent to the airport.
 
One of the Boulder (CO) reporting points was the IBM facility on the Diagonal Highway.
"Report IBM" ... "can't - I'm a Mac"
 
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