RNAV (GPS) aproach plate question

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WillFlyForFood

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WillFlyForFood
I recently notice on several RNAV (GPS) approch plates the notation "procedure NA for arrivals on XXX VOR/DME radials 298 CW 329." These radials are airways. This VOR is the IAF for the approach. There are LOC and NDB approachs to the same runway that have identical transitions from this VOR. Only the RNAV (GPS) approach has this note. The turn onto the transition is more than a 90' turn.

My theory is that the VOR is a flyover waypoint, and the protected airspace on the airways is greater than on the transition, which could allow an overshoot making the turn.

Why is this approach not authorized from these airways?
 
WillFlyForFood said:
I recently notice on several RNAV (GPS) approch plates the notation "procedure NA for arrivals on XXX VOR/DME radials 298 CW 329." These radials are airways. This VOR is the IAF for the approach. There are LOC and NDB approachs to the same runway that have identical transitions from this VOR. Only the RNAV (GPS) approach has this note. The turn onto the transition is more than a 90' turn.

My theory is that the VOR is a flyover waypoint, and the protected airspace on the airways is greater than on the transition, which could allow an overshoot making the turn.

Why is this approach not authorized from these airways?
Click to expand...

Most often cluelessness on the part of approach designers.
 
roncachamp said:
Most often cluelessness on the part of approach designers.
Click to expand...

Do you find atc will somehow issue an approach in such a condition? (arriving 'wrong way').
The way they write that, it sounds like "you can't get there from here", as there is no remedy offered, just a prohibition.

Ie; if you are prevented from getting that approach when arriving from the west, do they have no way of getting you east so it can be executed?

This is a good question, well - I've had it before too.
 
WillFlyForFood said:
I recently notice on several RNAV (GPS) approch plates the notation "procedure NA for arrivals on XXX VOR/DME radials 298 CW 329." These radials are airways. This VOR is the IAF for the approach. There are LOC and NDB approachs to the same runway that have identical transitions from this VOR. Only the RNAV (GPS) approach has this note. The turn onto the transition is more than a 90' turn.

My theory is that the VOR is a flyover waypoint, and the protected airspace on the airways is greater than on the transition, which could allow an overshoot making the turn.

Why is this approach not authorized from these airways?
Click to expand...

Welcome to POA! My guess is TERPS (Order 8260.3B ) allows 120° for an intercept angle (see par 220) using conventional ground aids, but RNAV routes are designed using Order 8260.58 instead. According to Volume 6, page 1-22 the maximum angle is 90°. Which, btw, doesn't completely explain why V287 (PAE 298°R) isn't allowed.

dtuuri
 
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Try it under VFR and see how your GPS handles it.

At Lafayette, IN (LAF) we have an ILS approach with an IAF named VAGES. Two weeks ago, we had a Citation crew abandon the approach and report the localizer inoperative. As it turns out, they were improperly cleared direct VAGES and cleared for the ILS Runway 10 approach from the east and slightly northeast of the airport. Their intercept angle was greater than 90 degrees to the next course.

According to the crew, the G1000 could not handle the transition from VAGES to the localizer and actually reset the localizer on the PFD. The crew had to abandon the approach and be re-vectored. When the crew debriefed inside, the captain said he had heard of this problem before.

I know the G1000 and G430 can handle greater-than-90 degree intercepts to T courses on RNAV approaches just fine, but I believe the problems become more evident when there is a conventional navaid involved with an RNAV course, such as the aforementioned RNAV Runway 34 at Arlington.
 
Let'sgoflying! said:
Do you find atc will somehow issue an approach in such a condition? (arriving 'wrong way').
The way they write that, it sounds like "you can't get there from here", as there is no remedy offered, just a prohibition.

Ie; if you are prevented from getting that approach when arriving from the west, do they have no way of getting you east so it can be executed?

This is a good question, well - I've had it before too.
Click to expand...

These notes are nonsense. Something like, "Procedure NA for arrival on ABC VORTAC airway radials 200 CW 300." Examine the plates and the charts and you typically find that the only way you'd find yourself on one of the affected airways is if you were headed for same other airport and elected to divert. If you did elect to divert you'd be recleared appropriately which would likely take you off those airway radials.
 
The turn onto the approach when coming in to the fix between the identified radials, the turn is too tight, to close to get the CDI to center on the approach before the next phase of the approach.

The protected airspace for the approach from a usable direction is not as large as what is required to make a large turn to get pointed in the right direction on the approach.
 
BillTIZ said:
The turn onto the approach when coming in to the fix between the identified radials, the turn is too tight, to close to get the CDI to center on the approach before the next phase of the approach.
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The note says "Procedure NA for arrivals on PAE VOR/DME airway radials 298 CW 329." If you're arriving on a radial that does not define an airway you're good to go.
 
I would assume ATC at some point before the VOR would have you on vectors, not the airway and the procedure is flyable.
 
dtuuri said:
It's just common sense. If those airways don't meet criteria nothing between them can either.
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Agreed. But the approach designers felt the word "airway" needed to be there. They must not possess common sense.
 
dtuuri said:
It's just common sense. If those airways don't meet criteria nothing between them can either.

dtuuri
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Common sense has nothing to do with it. If the quote

"Procedure NA for arrivals on PAE VOR/DME airway radials 298 CW 329."

is correct, it says nothing between them can be used.

CW means "clockwise," not "and." :mad2:

As used in Order 8260.19F - Flight Procedures and Airspace, it defines a "sector" not individual airways.
 
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midlifeflyer said:
Common sense has nothing to do with it. If the quote

"Procedure NA for arrivals on PAE VOR/DME airway radials 298 CW 329."

is correct, it says nothing between them can be used.

CW means "clockwise," not "and." :mad2:

As used in Order 8260.19F - Flight Procedures and Airspace, it defines a "sector" not individual airways.
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What is an "airway radial", and how does it differ from other radials? Why is this procedure authorized if inbound on the 330 radial but not the 329 radial?
 
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Okay, I have a question about this.

Say you ARE approaching the IAF from the wrong "NA" direction. If you are in a non RADAR environment......How do you turn around?
 
kgruber said:
Okay, I have a question about this.

Say you ARE approaching the IAF from the wrong "NA" direction. If you are in a non RADAR environment......How do you turn around?
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See AIM 5−3−5. Airway or Route Course Changes
 
roncachamp said:
See AIM 5−3−5. Airway or Route Course Changes
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I don't understand how this AIM section relates to turning around. It only seems to relate to leading a conventional turn in order to stay within the protected airway boundaries.

Can you explain this a bit more?
 
register@teamandras.com said:
I don't understand how this AIM section relates to turning around. It only seems to relate to leading a conventional turn in order to stay within the protected airway boundaries.

Can you explain this a bit more?
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Are you interpreting "turn around" to mean a 180 degree turn?
 
roncachamp said:
Are you interpreting "turn around" to mean a 180 degree turn?
Click to expand...

Yup. I take it I shouldn't?

Edit: I think I misunderstood Skywag's question. I'm now guessing that if you were approaching the PAE IAF from the wrong "NA" direction and in a non RADAR environment, as presumed in Skywag's post #20, you would fly the approach by going to SAVOY (also an IAF), do a hold-in-lieu of procedure turn at SAVOY, and then continue on the final course. Right?
 
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kgruber said:
Okay, I have a question about this.

Say you ARE approaching the IAF from the wrong "NA" direction. If you are in a non RADAR environment......How do you turn around?
Click to expand...
Use a different approach. Or maybe get Direct SAVOY. Really. Sometimes the answer to an approach question requires looking at more than the approach in a vacuum. I don't have a complete answer to this one but sometimes you have to figure out the right question.

Note that the "Procedure NA" prohibition does not exist when arriving at PAE from the same airways sector if executing the virtually identical LOC or NDB approaches (a huge 3° difference in the NoPT route form PAE to the FAC). So it is either (1) a mistake by the charting office (it happens) or (2) for a reason other than the degree of turn required.

Also suggesting there might be something else afoot is the fact that the MSA on the two plates are completely different. I don't see any terrain reason why the MSA to the southwest of the procedure is 2100 based on WATON LOM but 8100 for the entire circle if based on the threshold of runway 34. If you look at the ARLINTON Deaprture you see altitudes of 2,000 for that same area.

Sorry if that raises more questions than it answers... If you are really curious, the Charting Office is very responsive to questions like this.
 
register@teamandras.com said:
Edit: I think I misunderstood Skywag's question. I'm now guessing that if you were approaching the PAE IAF from the wrong "NA" direction and in a non RADAR environment, as presumed in Skywag's post #20, you would fly the approach by going to SAVOY (also an IAF), do a hold-in-lieu of procedure turn at SAVOY, and then continue on the final course. Right?
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Ta-da! :)

midlifeflyer said:
Use a different approach.
Click to expand...
:(

midlifeflyer said:
Or maybe get Direct SAVOY.
Click to expand...
:(

midlifeflyer said:
I don't have a complete answer to this one...
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You mean you didn't read post #7? :(
dtuuri said:
Welcome to POA! My guess is TERPS (Order 8260.3B ) allows 120° for an intercept angle (see par 220) using conventional ground aids, but RNAV routes are designed using Order 8260.58 instead. According to Volume 6, page 1-22 the maximum angle is 90°. Which, btw, doesn't completely explain why V287 (PAE 298°R) isn't allowed.

dtuuri
Click to expand...


midlifeflyer said:
Note that the "Procedure NA" prohibition does not exist when arriving at PAE from the same airways sector if executing the virtually identical LOC or NDB approaches (a huge 3° difference in the NoPT route form PAE to the FAC). So it is either (1) a mistake by the charting office (it happens) or (2) for a reason other than the degree of turn required.
Click to expand...
Couldn't it be that the RNAV chart is a more recent one with a realigned VOR and they're really the exact same course?

dtuuri
 
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