Question on this localizer approach at kvsf

There is a 74 degree turn to the Final course.. It is at DME 2 miles before the LOC to start your turn to intercept so you don't fly through the Final course.
 
It does seem to be just a nice to have "warning" for the localizer. It seems to me I've seen other approaches with intercept angles close to this that don't have a lead radial or a "fix in lieu of lead radial" so to speak. It can't really be mandatory to have COGUL on this approach otherwise DME required should be somewhere on the chart.

EDIT: or they could just call it LOC/DME approach. To self, read the whole dam plate dummy
 
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luvflyin said:
It does seem to be just a nice to have "warning" for the localizer. It seems to me I've seen other approaches with intercept angles close to this that don't have a lead radial or a "fix in lieu of lead radial" so to speak. It can't really be mandatory to have COGUL on this approach otherwise DME required should be somewhere on the chart.
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VSF.jpg
 
It's similar to a lead radial, but not exactly. The route from EEN starts from well outside the service volume of the localizer. Therefore, it is possible to receive false localizer indications along that route. The 26.7 DME fix is established to let you know when localizer indications are accurate. In other words, if the localizer needle starts coming in but you are only at, say 10 DME from EEN, you should not turn and follow it. However, once you get to 26.7 DME you can be assured it's a valid localizer signal.

I am looking for the reference.
 
RussR said:
It's similar to a lead radial, but not exactly. The route from EEN starts from well outside the service volume of the localizer. Therefore, it is possible to receive false localizer indications along that route. The 26.7 DME fix is established to let you know when localizer indications are accurate. In other words, if the localizer needle starts coming in but you are only at, say 10 DME from EEN, you should not turn and follow it. However, once you get to 26.7 DME you can be assured it's a valid localizer signal.

I am looking for the reference.
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That makes sense. I'd like to say I always listen closely to the IDENT to make sure I have the right one, but I don't
 
RussR said:
It's similar to a lead radial, but not exactly. The route from EEN starts from well outside the service volume of the localizer. Therefore, it is possible to receive false localizer indications along that route. The 26.7 DME fix is established to let you know when localizer indications are accurate. In other words, if the localizer needle starts coming in but you are only at, say 10 DME from EEN, you should not turn and follow it. However, once you get to 26.7 DME you can be assured it's a valid localizer signal.

I am looking for the reference.
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I couldn't find one as such. Could have been added by flight inspection.
 
aterpster said:
I couldn't find one as such. Could have been added by flight inspection.
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There are a lot of LOC/DME approaches with a long feeder route from a VOR where LOC intercept is not denoted by a DME fix and there is no concern of false LOC signals. If you find a reference, I suspect this is a requirement when the intercept angle exceeds 60 degrees with an arrival at the IAF and no procedure turn.
 
Clip4 said:
There are a lot of LOC/DME approaches with a long feeder route from a VOR where LOC intercept is not denoted by a DME fix and there is no concern of false LOC signals. If you find a reference, I suspect this is a requirement when the intercept angle exceeds 60 degrees with an arrival at the IAF and no procedure turn.
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I'll stick with my fight inspection assumption.
 
aterpster said:
I'll stick with my fight inspection assumption.
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That seems plausible, since Flight Inspection would catch false localizer indications that were evident on a particular approach.
 
Palmpilot said:
That seems plausible, since Flight Inspection would catch false localizer indications that were evident on a particular approach.
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Indeed. They have some very sophisticated electronics on those flight inspection airplanes.
 
Comparing approaches to other approaches with similar circumstances can be a real head scratcher sometimes. Often it just seems like new rules and procedures for charting happen, but charts don't all get updated at once. It seems that years can go before a procedure is due for its periodic check and then it gets updated to "this is how we do it now."
 
Clip4 said:
Why wouldn't flight inspection include a precauation against false LOC signal if that were the case?
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Why? You follow the chart by ignoring any localizer movement prior to COGUL.
 
Because a false LOC would make this approach unsafe for any aircraft given a intercept LOC clearance SE of the final course and not on the feeder. Not reporting a known hazard is a lawsuit waiting to happen.

You might also note that COGUL is both at a distance and HAA that make a false LOC highly unlikely.
 
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Clip4 said:
Because a false LOC would make this approach unsafe for any aircraft given a intercept LOC clearance SE of the final course and not on the feeder. Not reporting a known hazard is a lawsuit waiting to happen.

You might also note that COGUL is both at a distance and HAA that make a false LOC highly unlikely.
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No, I don't note that at all.

I receive this interim response from one of the folks responsible for this stuff:

"It probably is because of false courses. I’ll check in to it today and get back to you.

I agree, there is nothing in TERPS concerning lead DME. In fact, DoD wanted it included and petitioned AFS on it, but I complained that it needed to be in TERPS, and they never put anything in concerning it."
 
There used to be a lead radial from LEB VOR. Flight inspection submitted the request to change the lead radial to the COGUL DME fix. Because there is no criterion for a DME "lead" fix, it may go back to a LEB radial. I'm not holding my breath, though. :D
 
aterpster said:
There used to be a lead radial from LEB VOR. Flight inspection submitted the request to change the lead radial to the COGUL DME fix. Because there is no criterion for a DME "lead" fix, it may go back to a LEB radial. I'm not holding my breath, though. :D
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I wonder if Flight check didn't like the distance from LEB. That's about 37 miles out there. What is the +/- error they use for plotting out lead radials? 3.6? 4.5?
 
luvflyin said:
I wonder if Flight check didn't like the distance from LEB. That's about 37 miles out there. What is the +/- error they use for plotting out lead radials? 3.6? 4.5?
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3.6 degrees for crossing a radial. I too thought about the distance. The problem in this case is that the records don't have the flight inspection comments.
 
luvflyin said:
It does seem to be just a nice to have "warning" for the localizer. It seems to me I've seen other approaches with intercept angles close to this that don't have a lead radial or a "fix in lieu of lead radial" so to speak. It can't really be mandatory to have COGUL on this approach otherwise DME required should be somewhere on the chart.

EDIT: or they could just call it LOC/DME approach. To self, read the whole dam plate dummy
Click to expand...
What I was taught, and taught others in the AF was that the title of the approach only tells you what equipment you need to fly the final segment of the approach. So the DME in LOC/DME just means you need the DME for something on final. It would have no bearing on whether you needed to define anything before that (i.e. COGUL). You could have a TACAN arc to an ILS final, and it would still be called an "ILS RWY xx."
 
Sluggo63 said:
What I was taught, and taught others in the AF was that the title of the approach only tells you what equipment you need to fly the final segment of the approach. So the DME in LOC/DME just means you need the DME for something on final. It would have no bearing on whether you needed to define anything before that (i.e. COGUL). You could have a TACAN arc to an ILS final, and it would still be called an "ILS RWY xx."
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Well, this naming convention is no longer used. When this procedure is revised it will be LOC Rwy 05, and a briefing strip note "DME Required." And, down the road, where on the chart an equipment requirement note is placed with be dependent what it is required for. Lots of changes going on.
 
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