60-1 rule?
Joined: May 2000
Posts: 510
Likes: 0
From: New York
It's basic geometry. Nothing fancy. Very useful when flying some instrument approaches and easy to calculate on-the-run in your head. Also useful when using the tilt on the radar to figure out where the bottom of the beamwidth is at a certain distance from the aircraft.
At 60nm, radials are 1nm apart = 1 radial/nm
At 30nm, 2 radials/nm
At 15nm, 4 radials/nm
At 10nm, 6 radias/nm
As a practical application, say you were flying on a 15nm arc and wanted to know what you're lead radial should be to turn onto the course. Your speed is 180kts = approx 3nm/min. = approx 2nm turn radius.
Therefor, on a 15nm arc, 2nm turn radius = 8 radials (degrees) lead
At 60nm, radials are 1nm apart = 1 radial/nm
At 30nm, 2 radials/nm
At 15nm, 4 radials/nm
At 10nm, 6 radias/nm
As a practical application, say you were flying on a 15nm arc and wanted to know what you're lead radial should be to turn onto the course. Your speed is 180kts = approx 3nm/min. = approx 2nm turn radius.
Therefor, on a 15nm arc, 2nm turn radius = 8 radials (degrees) lead
Fleet Manager
Joined: Apr 2001
Aviation Qualifications: ATPL
Posts: 7,448
Likes: 310
From: various places .....
At the risk of confusing the issue, a bit more background.
For angles measured in radians, rather than degrees, the approximate relationship
sin (angle) = angle
(which holds for small angles) can be used to simplify the off track triangle geometry.
The basic geometry is
tan (TE) = distance off track / distance along track
which, for reasonably small angles, can be approximated by sin (TE). This, in turn, can be approximated by the angle in radians.
Now, it works out that, for small angles, this corresponds to a distance off track of x nm for a track distance of 57.3 nm (which, naturally enough, is then rounded off to 60 nm ... hence 1:60) if the included angle is x degrees.
For instance
1 deg = 0.017453293 radian, and
sin(1 deg) = 0.017452406
so the error is sensibly not too much of a problem.
Limitation is that the errors get out of hand as the angle gets bigger so, for practical use, 1:60 is useful for angles up to around 15 degrees or so .. ie normal DR nav problems.
For angles measured in radians, rather than degrees, the approximate relationship
sin (angle) = angle
(which holds for small angles) can be used to simplify the off track triangle geometry.
The basic geometry is
tan (TE) = distance off track / distance along track
which, for reasonably small angles, can be approximated by sin (TE). This, in turn, can be approximated by the angle in radians.
Now, it works out that, for small angles, this corresponds to a distance off track of x nm for a track distance of 57.3 nm (which, naturally enough, is then rounded off to 60 nm ... hence 1:60) if the included angle is x degrees.
For instance
1 deg = 0.017453293 radian, and
sin(1 deg) = 0.017452406
so the error is sensibly not too much of a problem.
Limitation is that the errors get out of hand as the angle gets bigger so, for practical use, 1:60 is useful for angles up to around 15 degrees or so .. ie normal DR nav problems.
Joined: Jul 2001
Posts: 28
Likes: 0
From: Scotland
Also useful for working out how many miles to fly around a DME arc procedure.
e.g. 12 dme arc (= 1/5 of 60)
If you are going to fly approximately 50 degrees of arc (you joined on the 295 radial, and your lead radial is 245 degrees from the beacon - you are flying south around the arc), then the distance on the arc will be about 10 miles. Gives you an idea how fast you can fly it, before slowing down and configuring for the turn inbound (some arcs are very much shorter of course).
Also can be used for working out how far off track you've deviated for weather avoidance or while on radar vectors, etc, as well as a whole heap of other things.
e.g. 12 dme arc (= 1/5 of 60)
If you are going to fly approximately 50 degrees of arc (you joined on the 295 radial, and your lead radial is 245 degrees from the beacon - you are flying south around the arc), then the distance on the arc will be about 10 miles. Gives you an idea how fast you can fly it, before slowing down and configuring for the turn inbound (some arcs are very much shorter of course).
Also can be used for working out how far off track you've deviated for weather avoidance or while on radar vectors, etc, as well as a whole heap of other things.
Joined: Feb 2005
Posts: 340
Likes: 1
From: KPHL
To add to what Linton said, the distances along the arc aren't subject to an increasing error with angle so you can keep using it for very large angles.
For example, if you flew 180 degrees of an arc at 12nm, the rule says you would fly (180/60)*12=36 nm. In fact you fly pi*12nm = 37.7 nm.
For example, if you flew 180 degrees of an arc at 12nm, the rule says you would fly (180/60)*12=36 nm. In fact you fly pi*12nm = 37.7 nm.
Joined: Jul 2006
Posts: 204
Likes: 0
From: 'tween posts
1 in 60 rule
something intresting I came across: circumference of a circle=2xpixR
where pi = 3.14... aproximated to 3. hence read the above eq as 6xR
standing at the center of a circle with a radius of 60nm gives you a circumference of 360nm (6x60=360). a circle consists of 360 dgs.
thus at a dist of 60nm:1dg=1nm. at 30nm 1dg=0.5nm. at 120nm=2nm.it was clear as mud at first but then i got the drift....
where pi = 3.14... aproximated to 3. hence read the above eq as 6xR
standing at the center of a circle with a radius of 60nm gives you a circumference of 360nm (6x60=360). a circle consists of 360 dgs.
thus at a dist of 60nm:1dg=1nm. at 30nm 1dg=0.5nm. at 120nm=2nm.it was clear as mud at first but then i got the drift....
Joined: Jun 2005
Posts: 278
Likes: 0
From: NY
interseting 
- never occured to me thats what I WAS doing ... twist ten turn ten is my mantra...
at first I thought it was the glide ratio used by a CURRENT Non-Boeing airframe manufacturer to suplemment those hair dryers on long hauls
- never occured to me thats what I WAS doing ... twist ten turn ten is my mantra...at first I thought it was the glide ratio used by a CURRENT Non-Boeing airframe manufacturer to suplemment those hair dryers on long hauls
Joined: Jan 2006
Posts: 179
Likes: 0
From: Australia
Limitation. 15Degrees.
I was told by a senior Ground Instructor that if The Track Error and Closing Angle Exceeded 15 Degrees not to employ the 1:60 Rule for ATPL Nav Exams, because it was an approximation of the Radial Rule. That a W/V had to be calculated and then applied to the new track to the destination.
