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#11
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On 9-Jul-2005, Newps wrote: The controller almost always eyeballs it. As for range rings they are alway displayed and are drawn around the radar site, not around an individual airplane. Of what possible use would range rings centered on the radar site be? From my memory of a visit a few years ago to a TRACON facility, I seem to recall that the controllers could get a reasonably accurate reading of distance from given fixes (e.g. VORs, OMs, airfields, etc.) by calling up range rings from that fix to appear on his/her scope. Given the level of digital sophistication they have available on the newer technology radar displays, that would be a piece of cake. Still, as you state, my guess is that most controllers, particularly experienced ones, usually eyeball it unless more precision is required. -- -Elliott Drucker |
#12
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On Sat, 09 Jul 2005 20:47:41 -0600, Newps wrote:
You have a digital readout that gives exact distance. The controller looks at the little space between you and the VOR symbol on the radar scope. That symbol, a circle, is about a mile in diameter. The controller looks at that space and he came up with 3 miles. He was off a mile. No big deal. Newps, Thanks for your reply. It may not be too big a deal from the ATC side, but one mile would be a big deal for a spam can like myself. As you know, some approaches require DME and if my equipment happens to be one mile off, then I may have problems if I was down to minimums and didn't see the airport because I was one mile short. Missed at MBO is just short of crossing mid field. Since my DG had gone south on me, I was even more concerned after passing the initial approach fix that maybe I could not rely on the DME since he "reverified" my distance from the VOR as 3 miles when I was reading 4. I realize that I was operating under VFR, so in my specific circumstances for today, it's no big deal, but had I been IMC, it would be more critical to know that my DME is working correctly. Seems that with airplanes, more then one part seems to go south at the same time..... Allen |
#13
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"A Lieberman" wrote in message ... On Sat, 09 Jul 2005 20:47:41 -0600, Newps wrote: You have a digital readout that gives exact distance. The controller looks at the little space between you and the VOR symbol on the radar scope. That symbol, a circle, is about a mile in diameter. The controller looks at that space and he came up with 3 miles. He was off a mile. No big deal. Newps, Thanks for your reply. It may not be too big a deal from the ATC side, but one mile would be a big deal for a spam can like myself. Its not a big deal if you realize that ATC isn't going to give your exact distance. 1) ATC is not responsible for calibrating your DME. 2) ATC assumes you will be able to figure out when you cross the VOR 3) This specific approach can use time to identify the MAP As a CFII, I always seem to have students with GPS and DME who feel compelled to question ATC for distance discrepancies of about a mile. After we visit an ATC approach control facility (its on my instrument syllabus) and see how controllers determine distance, that annoying habit usually goes away |
#14
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On Sun, 10 Jul 2005 11:45:48 -0400, Brad Zeigler wrote:
Hi Brad, See below comments. Keep in mind, I consider myself still new at instrument flying. Followups set to rec.aviation.ifr to maintain on topic. Its not a big deal if you realize that ATC isn't going to give your exact distance. 1) ATC is not responsible for calibrating your DME. Agree 100 percent 2) ATC assumes you will be able to figure out when you cross the VOR Agree 100 percent. That's what the to and from flags are for. So, the distance to the VOR did not concern me as I had the flags to help me identify the fix nor did I need a timer to verify the fix as I was being vectored. 3) This specific approach can use time to identify the MAP This is where I have additional questions. The time is based on a distance factor. The actual approach is the VOR A at MBO. I need 3 minutes 20 seconds to fly 5 miles from the JAN VOR to the MAF. Add in a headwind on the approach IF I have a discrepancy between what ATC is reporting and what my DME says, then I would think there is a potential problem, especially if ATC is reporting that I am closer then what my DME says. I do use all possible tools in my plane, and I do have a VFR GPS to help me determine ground track, so I can tell whether I should arrive to the MAP sooner or later then 3.20, but if didn't have that, wouldn't the accuracy of the DME be more critical since time would be skewed by wind correction? Now, by posting my concern to the newsgroup, I think I am learning that the DME would be an overriding factor on "who to trust" for distance determination. As I posted before, I never had come across a discrepancy before between my DME and what ATC reported. Hopefully I am right on my assumption that the DME is the overriding decision for accuracy?? Allen |
#15
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I have a 70's vintage Mitchell DG (with autopilot bug) that was drifting off
course rather quickly. After snooping around with Google groups to see which overhaulers had the best reputation, I sent mine off to Ducasse Aircraft Instrument Service in Pennsylvania for overhaul. It's been working great for the last 10 months. Expect it to be out of service for about 3 weeks even with air shipping. "A Lieberman" wrote in message ... Couple of questions. Went up to practice some ILS approaches. While being vectored for my approaches, my DG kept sticking through the 270 heading. First time on my initial approach and the second approach. Third and fourth approaches, DG acted normal, though seem a little off compared to the magnetic compass. (gave me good practice for partial panel approaches!). Also, my header bug seem to be frozen, couldn't move it at all. I ended up using my magnetic compass and VFR GPS for my primary navigation and tracking. I had this happen once on the ground a long time ago, and never gave any thought as it performed flawlessly in the air since. Vacuum gauge was exactly where it should be. Last thing I want to worry about in the clag is the DG. Is the DG worth overhauling or just getting a new one??? I went to http://www.aircraftspruce.com/menus/in/gyros.html to see what prices I am looking at, and it seemed all over the page in price. This would be a part obviously I don't want to cheap out on, but I don't want to buy a part that is has something in it I never will need. Suggestions much appreciated. I figured to post this time b4 going out on the limb. DME question. While on my VOR Alpha approach back to MBO, ATC reported me 3 miles from the VOR, and my DME reported me 4 miles. This is the first time I ever had a discrepancy that much. Anybody know what gives. My DME seemed correct as it reflected 5 miles to my airport. Allen |
#16
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john smith wrote: DME is slant range, ATC may be horizontal. How high were you? I was at 2000 feet, which is about 1700 AGL. Certainly not enough to give you an extra mile of slant range. You have a digital readout that gives exact distance. The controller looks at the little space between you and the VOR symbol on the radar scope. That symbol, a circle, is about a mile in diameter. The controller looks at that space and he came up with 3 miles. He was off a mile. No big deal. Another factor is the physical location of the DME site with respect to the airport reference point. How is that a factor? |
#17
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Newps wrote:
How is that a factor? If the DME antenna is at the end of the runway farthest from you on a long runway, the distance is greater. |
#18
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john smith wrote: Newps wrote: How is that a factor? If the DME antenna is at the end of the runway farthest from you on a long runway, the distance is greater. The controller will give a distance from a fix, almost always the OM or the FAF. It isn't relavant where the DME is actually located or how long the runway is, you still have to do some math to figure out how far you are from whatever the referenced fix is. |
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