Lead Radial

I've seen it many times.

Someone will come along with the book definition, but, as far as I know, it's the point at which you switch your workload/attention from the arc to intercepting the final approach course. You should have positive course guidance by the time you reach the LR, hence the unusual looking turn to intercept the final approach course.

If I'm off, be easy.
 
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When the angle of intercept exceeds 90 degrees, a radial which provides at least two miles of lead must be identified to assist in leading the turn on to the intermediate course
Click to expand...
- 80260.3B
 
The angle of intercept from an arc on a VOR approach is always 90 degrees assuming the arc is based on the same navaid as the approach. On an arc as short as 7 miles perhaps a 2 mile lead isn't provided by the OBS set to the inbound?
I'll have to look at some others? I looked at a few others, none that I found had lead radials but OTOH they were all longer arcs.
 
That's just what I read. I'll look into it further.
Quick way to calculate the Lear Radial:

Divide the arc DME into 60 then multiply the quotient by 1 percent of the ground speed

Example:
60/Arc DME = A

groundspeed x 1% = gs

A x gs = number of radials to lead by
 
peerlesscowboy said:
http://155.178.201.160/d-tpp/1410/05173V11.PDF
Putting my new charts in the brainbag this evening, noticed something I've never noticed before. I've flown this approach many times but not lately, when did they start putting lead radials on DME arcs to VOR approaches?, and why :confused:
Click to expand...
Nice reminder that the final intercept is coming so you don't have to calculate it yourself? Ore maybe a recognition that not everyone does a "turn-10-twist-10 all the way around the arc?
 
Same statement I quoted above was listed in the Instrument Procedures Handbook.

Here is a good article on it as well: http://www.terps.com/ifrr/may96.pdf

The published lead radial isn't all inclusive and will change greatly with groundspeed. Best to just calculate your own. I've used the formula I stated earlier and it has never steered me wrong. For the approach you provided, I guess the TERPS just wanted to provide one since it is a 7 DME arc(the lowest DME arc you will find on an approach)
 
peerlesscowboy said:
http://155.178.201.160/d-tpp/1410/05173V11.PDF
Putting my new charts in the brainbag this evening, noticed something I've never noticed before. I've flown this approach many times but not lately, when did they start putting lead radials on DME arcs to VOR approaches?, and why :confused:
Click to expand...

New one for me. Someone down in OKC being creative.

Lead radials are required when the course change is greater than 90 degrees (which would never be the case with a VOR/DME). Also required when the DME is not from the VOR used for the IAP. (very unusual).

They are also supposed to be on an ILS when a suitable VOR is located within siting requirements.
 
Gucci Pilot said:
That's just what I read. I'll look into it further.
Quick way to calculate the Lear Radial:

Divide the arc DME into 60 then multiply the quotient by 1 percent of the ground speed

Example:
60/Arc DME = A

groundspeed x 1% = gs

A x gs = number of radials to lead by
Click to expand...


I just visualize a 30 deg. intercept and interpolate the radial that gives me that.

That's another benefit of georef'd approach plates...makes it pretty easy to visualize the point at which a normal intercept should commence.
 
Gucci Pilot said:
That's just what I read. I'll look into it further.
Quick way to calculate the Lear Radial:

Divide the arc DME into 60 then multiply the quotient by 1 percent of the ground speed

Example:
60/Arc DME = A

groundspeed x 1% = gs

A x gs = number of radials to lead by
Click to expand...
Good trick. At 60 nm the lead-in radial would be 1.2° and 1.2 nm from the course. At 120 kts, a little over 30 seconds to intercept which is just about right for making a 90° turn.

Or, you could just time the CDI rate of movement and forget the math. Turn inbound when within 30 seconds of needle centered. :)

dtuuri
 
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peerlesscowboy said:
http://155.178.201.160/d-tpp/1410/05173V11.PDF
Putting my new charts in the brainbag this evening, noticed something I've never noticed before. I've flown this approach many times but not lately, when did they start putting lead radials on DME arcs to VOR approaches?, and why :confused:
Click to expand...

In case someone wants to look up the approach after the link expires, it's the VOR RWY 11 approach to Sloulin Field Intl (ISN) at Williston, North Dakota:

http://download.aopa.org/ustprocs/current/NC-1/isn_vor_rwy_11.pdf

The VOR/DME RWY 29 approach to the same airport does not have lead radials:

http://download.aopa.org/ustprocs/current/NC-1/isn_vor_dme_rwy_29.pdf
 
I agree that it is due to the lower radius on the VOR RWY 11 approach (compared to the VOR RWY 29 approach, for example). At that proximity to the VOR, when the CDI needle starts moving, I won't be able to make a standard rate turn to intercept the inbound radial. Thus a pre-calculated lead radial for pilot convenience.
 
Just in case the linked plates change in the future, here are their current versions attached as they are published today for your convenience:
 

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Cpt_Kirk said:
I've seen it many times.

Someone will come along with the book definition, but, as far as I know, it's the point at which you switch your workload/attention from the arc to intercepting the final approach course. You should have positive course guidance by the time you reach the LR, hence the unusual looking turn to intercept the final approach course.

If I'm off, be easy.
Click to expand...

Ditto.
 
LDJones said:
I just visualize a 30 deg. intercept and interpolate the radial that gives me that.

That's another benefit of georef'd approach plates...makes it pretty easy to visualize the point at which a normal intercept should commence.
Click to expand...

The count down timer in the screen of the 430W makes it pretty easy, too. :yes:
 
BigBadLou said:
Just in case the linked plates change in the future, here are their current versions attached as they are published today for your convenience:
Click to expand...

Even better!
 
aterpster said:
Any examples (other than this one) for a VOR IAP where the DME is from the VOR providing approach guidance?
Click to expand...
VOR/DME RWY 13 at Aberdeen, SD
http://155.178.201.160/d-tpp/1410/00642VD13.PDF
this is a 16 nm arc with lead radials

OTOH;
VOR RWY 22 at Alexandria, MN
http://155.178.201.160/d-tpp/1410/00014V22.PDF
here's a 7 nm arc without lead radials

There's others I find from just a casual page thru' of the NC-1 & NW-1, no pattern that I can see? Maybe it's just the "new/improved" chart clutter :confused:
 
dtuuri said:
Or, you could just time the CDI rate of movement and forget the math. Turn inbound when within 30 seconds of needle centered. :)
Click to expand...

You could do that, but if you use an RMI instead of the twist 10 turn 10 method, its a quick calculation to do without having to turn more knobs.
 
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Ghery said:
The count down timer in the screen of the 430W makes it pretty easy, too. :yes:
Click to expand...

Doesn't the IFR version of the metal landing calculator also provide a countdown timer? :D:goofy::D
 
peerlesscowboy said:
VOR/DME RWY 13 at Aberdeen, SD
http://155.178.201.160/d-tpp/1410/00642VD13.PDF
this is a 16 nm arc with lead radials

OTOH;
VOR RWY 22 at Alexandria, MN
http://155.178.201.160/d-tpp/1410/00014V22.PDF
here's a 7 nm arc without lead radials

There's others I find from just a casual page thru' of the NC-1 & NW-1, no pattern that I can see? Maybe it's just the "new/improved" chart clutter :confused:
Click to expand...

Have them with a 16 mile arc but not with a 7 mile arc. Makes a lot of sense, doesn't it. Actually, these procedures have been around for a few years. Maybe that was when Mr. Lead Radial worked there before going on to Burger King. :rofl:
 
Gucci Pilot said:
That's just what I read. I'll look into it further.
Quick way to calculate the Lear Radial:

Divide the arc DME into 60 then multiply the quotient by 1 percent of the ground speed

Example:
60/Arc DME = A

groundspeed x 1% = gs

A x gs = number of radials to lead by
Click to expand...
I admire this formula, however, can you Plz tell me where did this constant (60) come from..?!®
Plz send me on: engineerrawaha@yahoo.com
 
It comes from the approximation that 1 degree of turn represents an arc of length about 1/60 of the radius of the circle. It's really 1/57.2957549575... but that's close enough for a rule of thumb.
 
luvflyin said:
At least 45 years ago. So you dont overfly the inbound radial
Click to expand...
Wow, it only took 2 1/2 years for someone to answer that part of his question!

Unfortunately, he hasn't been here in over a year, so he probably won't see the answer.
 
Yeah, 1% of the ground speed. But don't most have guidance nowadays to lead the turn? Usually a wag will do, adjust AOB to make it work out.
 
Forget the math. Fewer and fewer of us are flying with RMIs. GPS, unless INOP, pretty much negates the need for turn-ten-twist ten to maintain the desired DME distance. Pay attention to the distance and adjust accordingly...adjustments on smaller arcs will be more frequent than bigger ones. It's a little easier to stay on or just inside the arc. Set the radial to intercept 5 degrees early (if you're flying a faster ship, then increase accordingly). On reaching it, set the radial to intercept (you'll have around a half-scale deviation) at which you should be good to start your turn to intercept. It's safe, and it works. Just make sure that you turn to intercept in the right direction.
 
Turn ten twist ten has always been just busy work. It's a DME arc, not a VOR DME arc.
 
MauleSkinner said:
Turn ten twist ten has always been just busy work. It's a DME arc, not a VOR DME arc.
Click to expand...
While it certaintly isn't required to fly a DME arc, it is a good way of maintaining SA on an arc in an airplane without a moving map depicting the arc...I used it when I taught IR students in older airplanes without GPS and when I flew single pilot 135 freight without GPS.
 
GCA319 said:
While it certaintly isn't required to fly a DME arc, it is a good way of maintaining SA on an arc in an airplane without a moving map depicting the arc...I used it when I taught IR students in older airplanes without GPS and when I flew single pilot 135 freight without GPS.
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I guess I never had issues figuring out which wingtip pointed towards the VOR. :)
 
GCA319 said:
While it certaintly isn't required to fly a DME arc, it is a good way of maintaining SA on an arc in an airplane without a moving map depicting the arc...I used it when I taught IR students in older airplanes without GPS and when I flew single pilot 135 freight without GPS.
Click to expand...
I agree with @MauleSkinner on make work. It one of those training things that make a DME arc far more complicated than it is. But unlike him, I sometimes don't know my right from my left. Even then though, I didn't do that many. One twist 10 after turning onto the arc as a crosscheck that I actually turned the right way. Lead radial at the end. Perhaps one or two random in the middle to monitor progress for situational awareness.
 
"Different strokes for different folks." I got my instrument rating in a plane that didn't have GPS. I found "turn ten, twist ten" quite helpful.
 
Palmpilot said:
"Different strokes for different folks." I got my instrument rating in a plane that didn't have GPS. I found "turn ten, twist ten" quite helpful.
Click to expand...
It can be. My gripe with the technique is the way it is sometimes taught, that the process of twisting is more important than the situational awareness it is supposed to produce. Realizing 10 is not some magic number opens up the thought process to the goal and how best to accomplish it given other workload tasks.
 
midlifeflyer said:
It can be. My gripe with the technique is the way it is sometimes taught, that the process of twisting is more important than the situational awareness it is supposed to produce. Realizing 10 is not some magic number opens up the thought process to the goal and how best to accomplish it given other workload tasks.
Click to expand...
I'll agree with that...realistically, I'd maybe twist a few times throughout the arc just to keep track of where I was at on it rather than every 10 degrees. The general principle behind turn 10 twist 10 is good though...Just as long as the busy work doesn't get in the way of the big picture.
 
GCA319 said:
I'll agree with that...realistically, I'd maybe twist a few times throughout the arc just to keep track of where I was at on it rather than every 10 degrees. The general principle behind turn 10 twist 10 is good though...Just as long as the busy work doesn't get in the way of the big picture.
Click to expand...
You will find that true of a lot of things, especially about instrument flight. IFR is so procedurally intensive (understandably so), we sometimes get caught up in the minutiae of the branches of the trees and never even see the whole tree, let alone the forest.
 
midlifeflyer said:
You will find that true of a lot of things, especially about instrument flight. IFR is so procedurally intensive (understandably so), we sometimes get caught up in the minutiae of the branches of the trees and never even see the whole tree, let alone the forest.
Click to expand...
I fought that battle quite a bit when I exclusively taught IR students at a large 141 flight school. They had a very...technical way of doing things and it frequently took the student's attention from the simple task of flying the airplane.
 
midlifeflyer said:
You will find that true of a lot of things, especially about instrument flight. IFR is so procedurally intensive (understandably so), we sometimes get caught up in the minutiae of the branches of the trees and never even see the whole tree, let alone the forest.
Click to expand...
Years ago my older brother and I flew to Colorado for a ski trip...he was working on his instrument rating at the time, and I was an ATP making my living in King Airs, so we decided I'd give him some instrument instruction on the way.
He was starting to mumble about the setup and calculations involved, and how he was going to figure out headings and stuff since he was partial panel ( :D ), so I pointed out that it's just a 90-degree turn onto the arc (30 seconds on needle & ball), and then 3- to 5-second turns when the DME increases to the arc distance. #1 VOR on the ILS, #2 set for the lead radial. He gave me one of those "wow! That's way easier than what I was taught!" looks.

That wasn't the only epiphany he had that trip...he also realized that while little brother still didn't stand a chance in a fair fight (my brother was a West Point grad/Army ranger at the time), I could make life pretty miserable for him under the hood. ;)
 
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