Judging distance during ground refrence
 

Hey everyone, I had an interview 2 weeks ago for a CFI position at a large 141 school in Arizona. It was my first CFI interview but Unfortuntately I didn't get the job (a whole different story), even though I felt I did good during the interview and sim session. Anyway, one of the questions that came up during the interview was, "How do you teach a student to judge they're distance when doing a rectangular pattern?" My response was by using a tree line that may be parallel to the field that we're using, and refrencing from that. Im from the midwest, and did all my training in the midwest so thats how I learned, fortnately, or unfortunately (i'm not too sure). Of course there's no tree's in the desert, so I'm not sure if this one thing was the nail in the coffin or what. It always worked well for me. But I was wanting to know what are some of other ways of teaching students how to judge their distance away from the field during these manuevers? I kinda feel dumb for not knowing any other methods, but as they say, as an instructor your not going to know everything.

A ground-ref maneuver by definition requires visual reference to the ground. It would be tough to do them without some readily-identifiable reference object. In the desert there are usually straight roads or power lines, if no trees.

But you can and should also use the heading bug as a guide, especially if you only have one reference and it's behind you.

If you're flying a pattern around an airport and you want to judge distance, how about using a straight reference object with a known length....... the runway.

Use the length of the runway as a visual ruler. So if you are using a 6,000' runway, and you desire to use a 1/2 miles spacing on your downwind (please don't teach anyone to fly wider patterns then this) you visualize half the runway length to get your downwind spacing

Yes @rickair7777 that was my explanation, that by using the tree lines that run parallel to the field that I would be teaching the Student "rectangular course" around, I would use those treelines as a visual refrence to judge distance that way, as many are 1/4 to 1/2 mile away from the field. I wasn't sure what answer the guy was looking for, or if he wanted me to "dumb" it down some more. I was completely understanding of the fact that trees don't grow in the desert and that there may be plants in place of the trees or of course power lines.

:) I wouldn't have said "tree line" if interviewing in the deert southwest, but rather geographical reference (much broader:)), then used the same logic that you applied, and others have suggested, of using known distances. Once you get some type of gouge reference you can apply it to different situations too - at a certain altitude, having something a certain point located at a position relative to the wing might be the quivalent of 1-2 or 1 mile.

@ alderdriver & jugheadf15 I didn't think about that until after the fact unfortunately, but you both are correct. After we discussed it, I was thinking something more along the lines of using the wing or pylon (if your flying a Cessna) as a refrence. @usmcflyer yes I totally agree and trust me it won't happen next time. Newbie idiot mistakes I guess, but if the question comes up again that will be a great way to think about it, as far as using the runway as a visual ruler to judge their distance away from a point, and yes my instructor always said "don't fly a 737 pattern", especially when it's busy.

I have an interview coming up this Monday in Florida and wanted to get some more insight on this, to at least know and have more ways than "using parallel tree lines".

2nd line of wing rivets on a Cherokee 180 at 1000 feet.

Seminolepilot,

A reference to a point on the wing or strut etc is useful, but you must realize that the reference is only valid at a given AGL altitude. If you use that same reference at a lower altitude, you spacing will be tighter than desired. This can easily lead to an overshoot to final. Classic examples of this can be seen during circling maneuvers. Keep the great attitude and effort in regards to learning. I have 35+ years, am a Master CFI, Military background and still enjoying and always strive to learn new flying techniques, etc.

From the USAF VFR portion of 11-217
A 60 degree angle equals AGL altitude x 1.7 in NMs
A 45 degree angle equals AGL altitude in NMs
A 30 degree angle equals AGL altitude x 0.6 in NMs

So at 1000' AGL in a C 172, half the strut is about 45 degrees equals about 1nm from the runway.

If the runway was 2/3 up the strut or just a bit below the tie down ring, then the pattern spacing would be TOO WIDE at about 1.7-1.9 nm from the runway.

If the runway was 1/3 of the way up the strut or a bit above the wheel, then you are a bit tight at about 0.6 nm from the runway.

YMMV

ive measured it with extended/offset track functions on various gps units. Which seat you are in and L vs R traffic skews things significantly. You can use the strut to judge distance, but its not as constant/consistent without taking these factors into consideration. Fairly consistently the people who claimed they were at 1/2 mile were usually at .75 or so. If I remember correctly about 1/2 up the strut if the runway is on your side, 1/3rd up the visible strut if it's opposite. May not be accurate from my memory! There are a lot of other ways to judge some of this stuff. Timing, known distances like the runway, etc.

You have mistaken the 45° equation: if you are 1000' AGL, looking down at a 45° angle to a point, you are horizontally 1000' from that point. You have formed an isosceles right triangle.

Distance = Rate * Time
 

This is a good time to re-enforce practical applications of the Distance / Rate / Time equations.

You should know the the speed of your plane, and your desired pattern size, you can describe the distance in terms of time.

Example: If you're in a C-172, at a pattern speed of about 90 kts, you're making about 1.5NM per minute (or about 1.7 statue miles per minute). If you want your downwind to be 1/2 mile away, parallel to the runway, that is about 17 seconds away.

Use some rough estimation, that you're still making distance in your turns, then you probably want your crosswind and base legs to be about 15 seconds.

I think you'll find that someone who cannot judge distance accurately can still estimate where they'll be in 15 seconds. Ask the student to count out loud to 15 on their cross/base legs, and decide if they are too close or too far.

Also, talk through the implications if they're going faster or slower; if they have a tailwind/headwind. Get them to actually pencil out the math, or make it an E6B exercise.

I only typed what I found in the USAF Manual from low level and VFR flying from the paragraphs to estimate distance. It seemed accurate enough. At 30,000 feet stuff that is a 45 degree angle away is certainly about 30 miles from the aircraft. It certainly isn't 6 miles away. But your geometry does seem correct. :confused:

TLAR method is all you really need:)