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#1
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Clearance: Direct to airport with /U
The other day I was flying to 3N6 in NJ from JST in PA in a plane with two
VORs and a VFR-only GPS. About halfway through I got an ammended clearance giving me a shortcut. The last point in the clearance was ARD then Direct 3N6. After accepting the clearance, and turning toward the next waypoint, I browsed further down on the chart, and realized that they omitted the feeder fix (RBV) in the ammended clearance. There is only one approach into Old Bridge, and the IAF is an intersection of RBV and COL, not ARD. It was a clear VFR day, so I didn't make a big deal of it, but I mentioned it to the final controller, and asked him to verify the vector that I picked off ARD, at which point he cleared me to RBV anyway. But did the controller who ammended the clearance without RBV make a mistake? Was it my mistake for accepting it? In IFR conditions, with a comm failure, would I have flown to ARD then RBV anyway? Should I have asked the controller for an ammendment as soon as I noticed the error? Or am I mistaken in recalling my instructor tell me that I can't fly direct to an intersection without some sort of RNAV unless I am first tracking one of the airways that make up the intersection. Thanks! |
#2
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On Fri, 27 Feb 2004 02:33:55 GMT, Judah wrote:
Or am I mistaken in recalling my instructor tell me that I can't fly direct to an intersection without some sort of RNAV unless I am first tracking one of the airways that make up the intersection. You are probably not mistaken in your recollection of what your instructor told you. However, it is likely that your instructor was not aware of the various methods of navigating directly to a fix without RNAV and without tracking one of the airways that define the intersection. I believe USAF pilots are still taught to do this. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) |
#3
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Hi Ron,
I would love to hear more about that technique. Now that you mention it, I could guess that it would resemble one of the techniques for flying a DME arc - flying perpendicular to radials from the VORs on the intersection, twisting the OBSes 10 degrees at a time until catching either one of the two airways or the intersection itself. Or maybe just dead reckoning it and waiting for the needles to swing, and following whichever airway you hit first in... Still, to my recollection, my instructor actually referred to some regulation that prohibited it. IIRC, the topic came up in a conversation about using an intersection as the first point in a flight plan... Still, if I'm off-track on the technique, I would love to hear more. Thanks! Judah Ron Rosenfeld wrote in : On Fri, 27 Feb 2004 02:33:55 GMT, Judah wrote: Or am I mistaken in recalling my instructor tell me that I can't fly direct to an intersection without some sort of RNAV unless I am first tracking one of the airways that make up the intersection. You are probably not mistaken in your recollection of what your instructor told you. However, it is likely that your instructor was not aware of the various methods of navigating directly to a fix without RNAV and without tracking one of the airways that define the intersection. I believe USAF pilots are still taught to do this. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) |
#4
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On Fri, 27 Feb 2004 07:29:56 GMT, Judah wrote:
Hi Ron, I would love to hear more about that technique. Now that you mention it, I could guess that it would resemble one of the techniques for flying a DME arc - flying perpendicular to radials from the VORs on the intersection, twisting the OBSes 10 degrees at a time until catching either one of the two airways or the intersection itself. Or maybe just dead reckoning it and waiting for the needles to swing, and following whichever airway you hit first in... Still, to my recollection, my instructor actually referred to some regulation that prohibited it. IIRC, the topic came up in a conversation about using an intersection as the first point in a flight plan... Still, if I'm off-track on the technique, I would love to hear more. Thanks! Judah I'd love to know what that regulation is. I've never heard of it but am willing to learn. Perhaps you could ask your instructor? My surmise is that it may be his own (mis)interpretation of the regulations. In any event, rather than re-invent the wheel, I'll post copies of two previous posts on this topic, in this newsgroup, and I'm sure you could find more explanations by using Google. The key is visualization. Ideally a slaved RMI would be the instrument to have, but you can do it with VOR/DME and other combinations of instruments: ============================ Explanation 1 (with RMI): It turns out to be quite straightforward if you have a slaved RMI. The technique uses the visual picture of the instrument to "plot" the solution to the triangle. This is easily demonstrated with an RMI in front of you, but I'll try to explain in words. First, lets explain how it works if the DME from the present position happens to be the same as the DME to the intersection. (This isn't how you really do it, but it makes the explanation easier). Imagine that the centre of the RMI represents the VOR station. Imagine that the airplane is attached to the tail of the RMI pointer. The tail half of the RMI needle represents the track from present position to the VOR. Now imagine a line from the center of the instrument out on the desired fix radial. Because we assumed that the distance from us to the station was the same as the distance from the station to the fix, we can see that the fix is on the rim of the RMI. Hold a pencil up to the RMI between the tail of the needle and where the imaginary line crosses the rim of the instrument. That's the third side of the triangle, so turn the airplane until the pencil is vertical (+/- drift). Now you are on track to the intersection. Of course in the real world you need to allow for different DME's, but the principle is the same. First figure out which is the bigger DME distance, the current indicated value or the DME at the desired fix. Define the radius of the RMI instrument is that distance. Work out the approximate proportion of the instrument face that corresponds to the smaller of the two distances. Now when we "plot" a position either for the airplane or the fix on the face of the instrument, adjust the distance from the center of the instrument that you hold the appropriate end of the pencil so that you make the correct shape triangle. (My apologies for this relatively poor explanation, but it's hard without visual aids). Once you are on-course for the intersection, refining your heading is made easy by the fact that it's going to be straight up the face of the instrument, so with a little practice you can correct by eye without needing to hold a pencil up against the RMI. And it is possible to achieve surprising accuracy with this method - you can hit within 0.1 nm of the fix fairly easily. Good enough for government work. Andy Davis ========================================= Explanation 2 (without RMI): Sigh. Not really. There are a number of ways of navigating direct to a fix, using an HSI/RMI and DME , a TACAN, or a VOR and DME. In fact, any one who carries an E6-B in his shirt pocket could go direct to a fix using the above reference navigation instruments. The technique is found in the Air Force AFM 51-37, which is the old manual. I understand that they have updated and changed the manual number. I'm sure any AF pilot can give us the current manual reference, and if anyone could rip off a new manual for me, I'd appreciate it! The following factors must be understood: 1. The station is located at the center of the compass card. 2. The compass rose simulates the radials around the station. 3. The aircraft position is visualized along the reciprocal (radial) of the bearing pointer. 4. The position with the greater range is established at the outer edge of the compass card. 5. The position with the lessor range is established at a point proportional to the distance represented by the outer edge of the card. In other words, if the outer edge of the compass card were a hundred miles, 50 miles would be half the distance to the outer edge of the card, 25 miles would be 1/4 distance, etc., etc. 6. Determine the no wind heading direct to the fix by connecting the aircraft position and the fix position with an imaginary line, i.e.., connect the dots. 7. Establish another line in the same direction, parallel to the original line through the center of the compass card. 8. Read the no wind heading to the fix under the lubber line. 9. Apply any known wind correction. The distance to the desired fix can be estimated since the distance between the aircraft position and the fix is proportional to the distance established from the center to the outer edge of the compass card. The same problem can be more accurately solved using an E6-B. You DO carry one right? Anyway, flip it over to the wind side, imagine that the center grommet is the station, and plot out your aircraft position and the fix position, draw or imagine a straight line between the fixes, rotate the card so the line is parallel to the direction your are fling, then read the no wind, direct heading under the arrow. To see if you have the concept, grab an E6-b and plot out this problem. 1. You are on the 180 degree radial at 50 miles. 2. The airport/fix is on the 270 degree radial at 25 miles. What is the no wind heading direct to the fix/airport? Have fun, hope this technique helps and gives you something to do on those long IFR/VFR cross countries. Norm (Melick) =================================== Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) |
#5
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I think you're both missing a key point here. Unless I misunderstood Judah's
original post, he was cleared ARD direct 3N6. So leaving ARD, you go direct to the airport - not to the IAF. Since the weather was good, the controller no doubt was counting on a visual approach to avoid sending you out of the way. If you want an instrument approach, you should request it. If unable to navigate direct, then request vectors, but from the enroute chart it looks like the ARD 090 would work pretty well.. There's no prohibition against accepting a clearance to go off airways direct to a fix, but ATC can only issue this if you're under radar control. Barry |
#6
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Did you file to the IAF in the original flight plan? If you wanted to do an instrument approach at your destination, you should have told the controller the clearance needed to be to that point and not directly to the airport. If they clear you directly to the airport, you can expect a visual approach if the airport is not the IAF. Don Brown wrote about something similar in his last AvWeb column. |
#7
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I've never received a clearance to anywhere but the destination airport.
Filing to an IAF might meet some psychic need, but ATC is going to put you where they want you, not to what you filed for. Bob Gardner "john smith" wrote in message ... Did you file to the IAF in the original flight plan? If you wanted to do an instrument approach at your destination, you should have told the controller the clearance needed to be to that point and not directly to the airport. If they clear you directly to the airport, you can expect a visual approach if the airport is not the IAF. Don Brown wrote about something similar in his last AvWeb column. |
#8
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"Judah" wrote in message ... The other day I was flying to 3N6 in NJ from JST in PA in a plane with two VORs and a VFR-only GPS. About halfway through I got an ammended clearance giving me a shortcut. The last point in the clearance was ARD then Direct 3N6. After accepting the clearance, and turning toward the next waypoint, I browsed further down on the chart, and realized that they omitted the feeder fix (RBV) in the ammended clearance. There is only one approach into Old Bridge, and the IAF is an intersection of RBV and COL, not ARD. It was a clear VFR day, so I didn't make a big deal of it, but I mentioned it to the final controller, and asked him to verify the vector that I picked off ARD, at which point he cleared me to RBV anyway. But did the controller who ammended the clearance without RBV make a mistake? No. Was it my mistake for accepting it? It wasn't a mistake at all, ARD direct 3N6 is acceptable routing. It was a nice day so the controller probably assumed you'd be happy with a visual approach. In IFR conditions, with a comm failure, would I have flown to ARD then RBV anyway? In those conditions you do whatever you need to do. Should I have asked the controller for an ammendment as soon as I noticed the error? It wasn't an error. If you wanted something else for some reason you should have advised the controller. Or am I mistaken in recalling my instructor tell me that I can't fly direct to an intersection without some sort of RNAV unless I am first tracking one of the airways that make up the intersection. What intersection would you fly direct to? The only portion of the route you mentioned was Yardley VOR/DME direct to 3N6. |
#9
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On Fri, 27 Feb 2004 08:57:52 -0500, "Barry" wrote:
I think you're both missing a key point here. Unless I misunderstood Judah's original post, he was cleared ARD direct 3N6. So leaving ARD, you go direct to the airport - not to the IAF. Since the weather was good, the controller no doubt was counting on a visual approach to avoid sending you out of the way. If you want an instrument approach, you should request it. If unable to navigate direct, then request vectors, but from the enroute chart it looks like the ARD 090 would work pretty well.. There's no prohibition against accepting a clearance to go off airways direct to a fix, but ATC can only issue this if you're under radar control. Barry Judah asked several questions in his post. I chose to respond to the question about what his instructor may or may not have said. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) |
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