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Definitions
The 60:1 rule is a method that can be used to determine the distance to (or from) a radio navigation station (an ADF or VOR).
Objective(s)
Use the 60:1 rule to determine the distance to a VOR and ADF station.
Description
- Basis for the 60:1 rule
- Visualizing how the 60:1 rule is used
- What information is needed to apply the 60:1 rule
- Solving 60:1 rule problems
Instructional aids
Content
Basis for the 60:1 rule
At 60 NM from a station, you travel 1 NM for every radial (1 degree) that you cross. If you cross 3 radials, you have traveled 3 NM. For this to work, you must maintain a constant heading.
Visualizing how the 60:1 rule is used
- The 60:1 rule allows you to formulate a proportion-type math problem: “If I was 60 NM from that station and I just crossed 10 radials, I would have traveled 10 NM. I don’t know how far I am from the station, but I do know I crossed 10 radials and I do know how much ground I covered while crossing those radials.”
- The graphic below (click to view the full-size, animated version) helps you visualize how the 60:1 rule can be used to determine the distance to a station. The first frame shows the 60:1 relationship; the second frame shows the relationship between degrees and distance; and the third frame shows how this can be plugged into a formula.
What information is needed to apply the 60:1 rule
- Problems that use the 60:1 rule will supply
- The number of radials crossed, and
- The distance traveled, or
- The true airspeed and time to cross the given radials (which is then used to calculate the distance traveled).
- The heading flown may be given, but is not important (except that a constant heading is maintained).
Solving 60:1 problems
This example is question COM474 from the FAA Commercial Pilot Test Question bank.
While maintaining a magnetic heading of 270 and a true airspeed of 120 knots, the 360 radial of a VOR is crossed at 1237 and the 350 radial is crossed at 1244. The approximate time and distance to this station are…
First, extract the information you need to solve the problem:
While maintaining a magnetic heading of 270 and a true airspeed of 120 knots, the 360 radial of a VOR is crossed at 1237 and the 350 radial is crossed at 1244. The approximate time and distance to this station are…
Write the formula that you will need to solve this problem:
60 NM / 1 degree = (??? NM from station) / ( ??? NM traveled)
You know that you crossed 360-350=10 degrees, and that 1 degree = 1 NM if you are 60 NM from the station:
60 NM / 10 NM = (??? NM from station) / (??? NM traveled)
The distance you traveled to cross those 10 radials is calculated from your TAS and the time in minutes
- At 120 NM / hr, you are traveling (120 NM/hr) x (1 hr/60 min) = 2 NM/min
- Your distance = (2 NM/min) x (1244 – 1237 min) = 14 NM
Your distance formula now becomes:
60 NM / 10 NM = (??? NM from station) / (14 NM traveled)
Solve this problem as you would any other algebraic proportion:
(60 x 14) / 10 = 84 NM
Time to the station can be calculated using the V=d/t formula
Real-life advice and experience
- You either don’t have an ADF or VOR receiver onboard to apply this rule, or you have a GPS that gives you the information you need to know. This is just for CFIs and commercial students to use on the FAA knowledge test.
- This method works equally well if you are passing ADF radials.
- This method does not apply for problems where:
- The relative bearing to an ADF changes 45 degrees (use the isosceles triangle method); or
- The relative bearing doubles (use the isosceles triangle method); or
- A course change is involved.
- This formula isn’t exactly correct, especially if you cross many radials or if I get close to the VOR!!! [see why]
Additional resources
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#1 by Mike Franz on March 19, 2010 - 12:10
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Yo, Chris, you are correct in theory with the exception of flying a constant heading! Think about this, If you crossed 20 radials flying a constant heading ( no wind for now) you would not be the same distance from the nav aid unless you flew an arc(like a DME arc). Pull out a sectional, go to a VOR, pick a radial and about 60 miles out draw a course line perpendicular to the radial. Then measure the distance along a radial 20 degrees different. Or measure from the nav aid to a point on the line of +20 degree radial. It will be a greater distance.
#2 by Chris on March 19, 2010 - 12:45
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No surprise here: you are absolutely correct Mike! As you point out, if you start 60 nm from the VOR and fly on a constant heading until you cross 1 radial, you won’t be 60 nm from the VOR anymore…you’ll actually be a little further from it (use the Pythagorean theorem to figure out that you’ll be 60.008 nm). This error grows as you cross more radials–by the time you crossed 20 radials, you would in fact be 63 nm from the VOR.
If you fly over just a few radials, the difference is pretty small. You can cross 12 radials be within 2% of the correct distance, which isn’t too bad. Over 20 radials (at 60 nm), the difference gets to be >5%. Just from doing a few sample calculations, it looks like most of the time, if you don’t cross too many radials, you can estimate your distance to within +/-5%. One of the problems that I have with the explanation of the 60:1 rule in the Jeppesen book is that they don’t explain the rationale behind it, but instead just slap out some formulas. If that’s all you know, then 1) it’s harder to solve 60:1 problems and 2) you wouldn’t be able to recognize limitations to the method, like this particular one.
Now the sad reality: this probably won’t ever be more than a test question for most guys, and one that could be memorized (there are only a few of these questions on the knowledge exam). In that case, you aren’t trying to figure out if you’re over airport A or airport B, you’re trying to select between answer A and answer B.
The 60:1 problems are neat to think through…thanks for raising this important caveat!
#3 by Mike Franz on March 20, 2010 - 12:53
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Dear Chris, I found the 60:1 rule useful during cross country instruction to stress the importance of flying a desired heading. I tell pilots that are constantly off the desired heading that if they are off course just 5 dgrees in a 120nm flight we can be 10 miles off at the expected time of arrival. Hopefully many would use good navigation enroute to make off course corrections and fly a desired heading. This was especially important on a VFR flight from Miami to Puerto Rico when spending a lot of time over open ocean with NO reference points and trying hard not to mistake the shadows from clouds as islands in the distance.
#4 by Chris on April 1, 2010 - 10:16
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I added the emphasis in your post Mike. I remember watching a documentary about SR72 pilots. The one quote I remember is that “1 or 2 degrees is the difference between a successful mission and an international incident.”
#5 by Mike Franz on March 20, 2010 - 12:58
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As to your beginning post about 60:1, most helo pilots will not be at suffient altitude to be 60 miles from a VOR and receive the station. Therefore my mention of flying an equi-distant arc really does not apply as your math showed how small the error would be. 60:1, 30:.5, 15:.25