tag:blogger.com,1999:blog-10000144.post8097166263193889499..comments2024-03-13T09:47:40.487+00:00Comments on Cockpit Conversation: Magnetic North is Not the SameAviatrixhttp://www.blogger.com/profile/13634111275860140084noreply@blogger.comBlogger16125tag:blogger.com,1999:blog-10000144.post-2566721416110291392011-06-27T20:44:40.564+00:002011-06-27T20:44:40.564+00:00Probably a weird question to ask here, but does an...Probably a weird question to ask here, but does anyone know this site? Did anyone order a shirt here? The shirts look really good but I don't know if I can trust the site <a href="http://www.pilotbooth.com" rel="nofollow">www.pilotbooth.com</a>Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-10000144.post-58100622312582097922011-06-20T20:40:36.179+00:002011-06-20T20:40:36.179+00:00A Squared: No, at the code level, the navigation i...A Squared: <i>No, at the code level, the navigation is being done in Earth centered Earth Fixed Cartesian coordinates, the inherent reference system of GPS. Magnetic heading, and latitude/longitude for that matter are all computed for display.</i><br /><br />Of course the GPSs internally work in ECEF coordinates but I wasn't talking about that: I was talking about the <i>procedures</i> which are published as magnetic radials. However, as I recall a single variation is used for the whole procedure so you can wind up using a nav aid with a different variation for a GNSS procedure as for a normal one.Edhttp://edavies.me.uk/noreply@blogger.comtag:blogger.com,1999:blog-10000144.post-16638290215795217212011-06-19T08:38:44.850+00:002011-06-19T08:38:44.850+00:00I've been flying for only a few years and here...I've been flying for only a few years and here in France I know a few airstrips which numbers have changed because of magnetic North changed.<br /><br />It's not uncommon.<br /><br />I'm very happy to fly in a place where the magnetic declination is 0° :-) (well it's between 0° and 5° so in practice for my little VRF flights I can usually neglect it).patghttp://pilotaillon.over-blog.comnoreply@blogger.comtag:blogger.com,1999:blog-10000144.post-74914220239170753912011-06-18T15:58:18.750+00:002011-06-18T15:58:18.750+00:00zb: Yes, as Sarah attests, it is not an everyday o...<b>zb</b>: Yes, as Sarah attests, it is not an everyday occurrence, but eventually magnetic north shifts far enough that the runway heading is no longer within 5 degrees of its number and it gets changed. Sometimes at night you can see the painted out numbers underneath.Aviatrixhttps://www.blogger.com/profile/13634111275860140084noreply@blogger.comtag:blogger.com,1999:blog-10000144.post-21537154848101834562011-06-18T12:25:35.103+00:002011-06-18T12:25:35.103+00:00Yes, zb - our local international used to have 29L...Yes, zb - our local international used to have 29L/R parallels. They're now 30L/R.Sarahhttps://www.blogger.com/profile/09991660841701835065noreply@blogger.comtag:blogger.com,1999:blog-10000144.post-67350460486592379762011-06-18T08:06:48.121+00:002011-06-18T08:06:48.121+00:00I wonder if the big white letters painted on runwa...I wonder if the big white letters painted on runways have ever been changed somewhere because magnetic North has shifted.<br /><br />One thing that amazes me about air-navigation (to make a word out of words) is how everything, be it ever so high-tech, is built to be in perfect harmony with what was used in the first half of the 20th century.<br /><br />Yay for interoperability.<br /><br />However, making true North the norm would probably not even mess with the idea of having DC-3s and A321s find the same runway, using some different navaids.zbnoreply@blogger.comtag:blogger.com,1999:blog-10000144.post-47680239948437914782011-06-18T05:39:52.997+00:002011-06-18T05:39:52.997+00:00Actually, yes they do. All you have to do is add t...<i> Actually, yes they do. All you have to do is add the variation.....</i> <br /><br />Sigh.... OK yeeees, it *is* possible to *compute* true north by adding variation to magnetic heading. I assumed that was obvious to all. <br /><br />Allow me to rephrase: <br /><br />Because the vast majority of planes flying have no means of *directly* determining the aircraft's orientation relative to true north, by sensing true north. <br /><br />Better?<br /><br /><i> For GNSS (GPS) procedures we have the ridiculous situation where variation is deliberately added in to headings to be subtracted out again.</i> <br /><br />No, at the code level, the navigation is being done in Earth centered Earth Fixed Cartesian coordinates, the inherent reference system of GPS. Magnetic heading, and latitude/longitude for that matter are all computed for display.A Squarednoreply@blogger.comtag:blogger.com,1999:blog-10000144.post-34510844508031418252011-06-18T05:27:47.629+00:002011-06-18T05:27:47.629+00:00I'll see if I can find out if anyone else does...<i> I'll see if I can find out if anyone else does this, or it's Canada alone. </i> <br /><br />The runway direction at Thule, Greenland is true.A Squarednoreply@blogger.comtag:blogger.com,1999:blog-10000144.post-83782563564575781182011-06-18T01:28:03.149+00:002011-06-18T01:28:03.149+00:00It should be noted for the purpose of this discuss...It should be noted for the purpose of this discussion that Canada <i>does</i> use true north navigation north of a line I may find for you later. The runway numbers have a T in them to remind pilots that they are true. I'll see if I can find out if anyone else does this, or it's Canada alone.Aviatrixhttps://www.blogger.com/profile/13634111275860140084noreply@blogger.comtag:blogger.com,1999:blog-10000144.post-72047157209649565212011-06-17T19:49:44.463+00:002011-06-17T19:49:44.463+00:00Reading Aviatrix's post about the Vancouver VO...Reading Aviatrix's post about the Vancouver VOR's compass rose being rotated 4 degrees (a significant amount) and the change being announced via NOTAM stuck in my craw. Pilots need the best possible tools to avoid flying into high-altitude, crunchy clouds -- which are plentiful near Vancouver. Rotating VOR radials is at best a temporary solution.<br /><br />I mean, we're talking about Canada, the Home of the Wandering Magnetic North Pole and the Land of Squirrelly Compasses. If any nation has an impetus to lead the way to standardization on true north navigation, Canada does. It's not 1935 any more.<br /><br />If if those of us living south of the border are really lucky, our nation might take notice and adopt true north navigation as well. Although, given that we're still measuring temperatures in Fahrenheit and buying food by the pound, I'm not going to hold my breath.DataPilothttps://www.blogger.com/profile/11478857340951784073noreply@blogger.comtag:blogger.com,1999:blog-10000144.post-65447473368296639162011-06-17T11:14:47.620+00:002011-06-17T11:14:47.620+00:00Perhaps part of the explanation for the enduraance...Perhaps part of the explanation for the enduraance of Magnetic in a (developed) world of satellite aids is that in that other world many many people are obliged for a variety of reasons to navigate - in the generic sense - in a much less sophisticated surface environment .Dafyddnoreply@blogger.comtag:blogger.com,1999:blog-10000144.post-91866090017326278372011-06-17T09:58:09.063+00:002011-06-17T09:58:09.063+00:00Because the vast majority of planes flying have no...<i>Because the vast majority of planes flying have no means of determining the aircraft's orientation relative to true north.</i><br /><br />Actually, yes they do. All you have to do is add the variation (difference between true and magnetic) to the reading from the compass. You're supposed to correct for deviation (compass errors) anyway so why not one more step.<br /><br />It always seemed to me that the best way would be to have a little knob (non-magnetic!) which you turn to set the position of the lubber line on the compass to match the variation.<br /><br />I think IRS equipped aircraft do determine true north by sensing the Earth's rotation and the local gravitational field while they're aligning.<br /><br />For GNSS (GPS) procedures we have the ridiculous situation where variation is deliberately added in to headings to be subtracted out again.<br /><br />Use true.<br /><br />(And why do we CC e-mails? When did you last use any carbon paper?)Ed Davieshttp://edavies.me.uk/noreply@blogger.comtag:blogger.com,1999:blog-10000144.post-79752845216115010802011-06-17T06:38:44.281+00:002011-06-17T06:38:44.281+00:00Data pilot,
Unless you're flying an airplane ...Data pilot,<br /><br />Unless you're flying an airplane which navigates from an inertial reference, your heading indicator, gyroscopic or not, is oriented to a magnetic reference, is by a device that senses the earth's magnetic field. <br /><br /><i> Does anyone know why we don't use true north for all navigation? </i> <br /><br />Yes. Because the vast majority of planes flying have no means of determining the aircraft's orientation relative to true northA Squarednoreply@blogger.comtag:blogger.com,1999:blog-10000144.post-65777458774384185572011-06-17T05:21:23.742+00:002011-06-17T05:21:23.742+00:00Oddly, I never asked that question. I believe we n...Oddly, I never asked that question. I believe we navigate by coordinates based on magnetic north because we are following in the unbroken tradition established when someone (some ancient Phonecian? Who discovered the principle of the magnetic compass?) discovered a way to maintain a course on a cloudy night. <br /><br />It would kind of make sense to switch. It wouldn't actually put more work on the people navigating with compasses, because the <i>charts</i> have gridlines on true north, so we plan in true and convert to magnetic anyway.<br /><br />It would definitely be one for old captains to annoy their young FOs about in reminisce.Aviatrixhttps://www.blogger.com/profile/13634111275860140084noreply@blogger.comtag:blogger.com,1999:blog-10000144.post-38891340892688450502011-06-17T04:21:02.577+00:002011-06-17T04:21:02.577+00:00As someone who flies antique aircraft (a 1943 J3 c...As someone who flies antique aircraft (a 1943 J3 cub and 1946 Champ) I say hrrrmph!<br /><br />You can navigate by compass, it's a little wiggly and all, and maybe not too accurate. But I'm a student and I've used it just fine for my cross country trips. I'm also only travelling at a meager groundspeed so it takes quite a lot longer to accumulate any serious errors.<br /><br />On the flip side, it's not like I'm using a VOR anytime soon unless I buy a handheld that does that.<br /><br />Of course the whole ATIS is magnetic but METAR's are true would go away too.Chris Prosserhttps://www.blogger.com/profile/00407859630135136398noreply@blogger.comtag:blogger.com,1999:blog-10000144.post-80022170297887455012011-06-17T03:03:16.473+00:002011-06-17T03:03:16.473+00:00I always hated it when my students asked me to exp...I always hated it when my students asked me to explain why magnetic headings were used for just about everything -- runways, NavAids, and so on. I hated that question because I could never provide a satisfying answer. I'd usually respond with something along the line of, "Runway headings are magnetic because some (ancient) planes don't have gyroscopic heading indicators, and the poor pilots flying them have to navigate by the magnetic compass." <br /><br />Thirty years ago, most students bought that explanation. Maybe they bought it because GPS units were not available to civilians at any price back in those days. Or, perhaps they were just being polite. Heck, I don't know.<br /><br />I never could figure out how to respond to astute students that pointed out that you can't really fly according to a magnetic compass anyway, unless the air happens to be perfectly still. Turning and turbulence will make the compass swing all over the place, and besides, you have to correct for the crosswind. Why not forget the plight of pilots flying antique aircraft, set all gyro compasses and runway headings to true north and be done with it? And while we're at it, why don't we standardize all VORs and ILSs and other NavAids to true north as well?<br /><br />Does anyone know why we don't use true north for all navigation? Other than because that's the way it's always been done in the past?DataPilothttps://www.blogger.com/profile/11478857340951784073noreply@blogger.com