Airport runway names shift with magnetic field
ncei.noaa.gov
ncei.noaa.gov
[0] - https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml#d...
Flying a great-circle route that intersects the North Pole, and magnetic North Pole, would mean travelling both north and south at the same time for a period.
It's perhaps unfortunate that we live in an era where they are "close enough" that we have one word (North) for two different directions.
Is it possible for the magnetic poles to ever exist far from the geographic poles? (I know the magnetic field could have been the opposite polarity, or not existed at all, but in either of those cases, we still wouldn't have gotten another word.)
The north magnetic pole has been south of 70 degrees as recently as the mid-1800s and the south magnetic pole is currently north of 65 degrees. Every half million years or so the whole thing goes nuts for a while and reverses.
I don’t think the exact mechanics of the magnetic field are super certain, but the general idea is that the rotation sort of pins the poles nearish to the axis but there’s been some significant variation historically.
There might be a very large metal deposit close to the surface (like in Sudbury) that upsets the local magnetic domain.
If you are in the UK you might be interested in Standup Maths’ video https://youtu.be/HcFvegnQpPo.
Currently true north and magnetic north are broadly the same in the UK - and over the next year or so, there is a point where grid north (Ordnance Survey maps) also coincides with both other “norths”. That point will track north over the UK.
The video shows Matt visiting Cornwall at a place where that point was.
Ref: https://www.sco.wisc.edu/learning-center/magnetic-declinatio...
Note it doesn't work with an adblocker enabled. (I don't think the API to show the maps is free.)/
Related, during the last two weeks or so I've been immersing myself in exploring the topographical maps of Bulgaria the Soviets drew towards the end of the '80s (it was for a personal project of mine). For those interested the map can be found in here [1], by scrolling further down the page, a typical map-sheet looks something like this [2]
[1] http://web.uni-plovdiv.bg/vedrin/index_en.html
[2] http://web.uni-plovdiv.bg/vedrin/details/large/K-35-016-3.jp...
The difference between them depends on where you are on the globe - it could even be 180 if you happen to stand in the middle of the two!
Magnetic compasses always point to magnetic north, but with earth being molten metals - magnetic north likes to move around a bit, so we work out the difference between the two and apply it to the directions we track.
For example, where I am - the difference is around 11 degrees. In order to head directly west, I can't just let my compass point north and go directly perpendicular port - I have to point north plus 11 degrees, and then go. My actual track will be 281 degrees magnetic, not 270.
What's more interesting is that most navigation charts have all their directions and bearings in "true" north, with the variance also charted, whereas when you actually fly you track the magnetic headings plus/minus the variance. If you go long enough - the variance also changes so you have to take that into account when planning your route.
When you take off / land, runway headings directly corresponding to your heading are a good sanity check - alarm bells go off if you're meant to be flying west but come across Runway 09 in front of you (the opposite!), not to mention we still rely on magnetic compasses - you don't want to be coming into land at a track for 281 degrees and see 27 painted on it; chances are something went wrong somewhere.
Example, San Francisco US, SFO (37°37'08"N 122°22'31"W), to Granada Spain, GRX (37°11'19"N 3°46'38"W) would go north of Newfoundland Canada:
The 1st place plane took off after the 2nd place plane. This happened because the navigator of the 2nd place flight didn’t take into account the great circle distance and flew straight headings.
(looks at map of Pacific)
Hang on ... where did the earlier ones stop?
For short manually planned tracks (eg VFR planning), most people will plan from one visually helpful waypoint to another, and measure the heading at the mid-point of each route segment. The midpoint approximates the GC heading, and anyway the discrepancy is (very) small on short segments.
For long tracks (eg IFR interstate or intercontinental flights), most plans comply with standard routes, between nominal waypoints, and the route segments together may approximate GC tracks. Between each waypoint, one normally flies a constant heading.
This is imperfect, but variations due wind and traffic are far bigger than losses due not quite conforming to a GC track.
Press GPS direct button and don’t bother ;) ;) ;)
It seems like it could be confusing over time to keep updating runway names as flight paths are repeatedly flown by generally the same sets of pilots, and as paths becomes familiar. For fancy autopilot setups most of the in-the-moment thinking is avoided and this may become a very minor detail.
Edit: Thanks for the quick info everyone! Now this makes sense. Happy holidays :)
Also so there’s no confusion, each direction is named, so a runway that runs due North-South will be Runway 36 in the northern direction, and 18 to the south.
In practice it is rare for all but the largest airports to have more than 3 or 4 runways so it isn’t like there will be a Runway 2 and a Runway 3 at the same airport. If they need more capacity they’ll build parallel runways which will be named with a suffix, like 9L and 9R.
(Also, magnetic compasses aren’t that accurate in the first place, since there’s iron in the engines if nothing else. In theory there should be a compensation/calibration done with the results on a card, but, no guarantees that it’s done or up to date).
There are even some airports that have three runways with the same heading, so they have "L", "C", and "R". (Two examples that I've personally took off or landed on all three of are 17/35 at DFW and 01/19 at IAD.)
There would be no (or extremely rare, at a minimum) operational reason to alternate directions for takeoff and landings on parallel runways. (There are rules for simultaneous operations to parallel runways and having them be in opposite directions would be problematic as you have to assume some aircraft will execute a missed approach and would then be climbing into opposite direction landing traffic with only a small lateral offset.)
In fact, taking this dodge into account, the DFW example I gave actually has five parallel runways; the two they label 18/36 are actually the same heading as the three they label 17/35. I wonder if they'll ever need to go to six and add an 18/36C.
Doing that for 4 would need one direction to be A B C D and the other to be B C D E (which is workable, but doesn't seem particularly more elegant than just using left, right, and center [and in fact is worse in some ways, since from one direction, B is the left-most and from the other, it's A])
Then you have airports like ORD which have more than three parallel runways - but pretend some of them are ten degrees off to get more naming space. [1]
[1] https://upload.wikimedia.org/wikipedia/commons/a/aa/FAA_O%27...
My flight instructor once switched off the electricity to the airplane's controls and radios and told me to land. At an airport with a control tower. Using the magnetic compass, airspeed, barometric altimeter, RPMs, that's it. Nothing else works without electric power. There's a whole procedure for doing all that. Being able to navigate safely with an old-school magnetic compass is life-critical.
You just pre-arrange it with the tower and it's no big deal. Probably exceptions for busy class Cs or Ds, but it's no big deal to any airport near me.
Also, in the real world, i would probably break out my smartphone. Short of an emp strike, it will still run on its own battery and can act either as a rough set of instruments or to phone the tower and declare an emergency.
Planes also a normal compass as their ultimate backup instrument, which of course is also magnetic.
Finally, while modern systems could operate off true north instead, not ALL planes have that.
Also, winds (and just about everything else) are in magnetic degrees. If I have wind from 280 while I'm landing, then I immediately know that I have a left quartering headwind and what to expect.
Not always: "If you read it, it's true. If you hear it, it's magnetic."
Actually, it's more like "310ish". Both 305 and 314 are acceptable readings for a runway 31.
Edit: forgot 2 HSIs ;)
So the numbering is a useful backup and discriminator, but the charts have much more detail, and modern navigational and instrument systems on runways obviate much of this for most flights anyways.
As a side note, modern avionics like G1000 auto sync your heading indicator to magnetic. So if we started flying with electronic avionics that are auto synced and have a database of magnetic variation around the world, then it’s feasible to always show true on the heading indicator and have runways and everything else be true bearings. But that’s not the case and I still fly some of the many steam dial planes out there as do others, so we’re stuck with magnetic runways and magnetic everything else used in real-time flight and situational awareness for pilots.
Thread with details here: https://twitter.com/lemonodor/status/1508505542423064578
A short summary is that sometimes when ATC radars see an aircraft, if it doesn't seem to have ADS-B (is in a position where no known ADS-B-equipped aircraft is), it will create a synthetic target, broadcasting it out so that aircraft with ADS-B In can see it on their traffic displays. That system is called TIS-B. Somehow the radar in Islip got confused by the magnetic declination: it was generating TIS-B targets that were rotated 13 degrees from where the aircraft really were. And it was doing it for pretty much every aircraft, whether or not it had ADS-B. I assume it wasn't able to correlate the known ADS-B position with the secondary radar returns because they were offset by 13 degrees.
Very weird way for a pretty important piece of ATC infrastructure to fail.
None the less I'd (semi educated) guess that someone at the rader site in question "updated" | "improved" the implementation of The World Magnetic Model [1] in use there and effectively dropped the correct corrections from the end result (for a few days until it was noticed and fixed).
Normally coefficient sets are updated every five years .. and frequently sites and software that use the WMM find themselves with a current IT support person that has not previously encountered a WMM update and then backtrace their way into an "understanding".
This can cause errors until noticed.
Critical infrastructure places (Military, Air Traffic Control, etc) tend to fare better and have longer periods of staff retention, etc. but it can still happen that "we no longer have anyone that was here the last time (five years ago) this happened"
However; given the last epoch update (WMM2020) was released 12/10/2019 (in 'merc date speak MM/DD/YYY (barbarians)) and remains current until expiring on December 31, 2024 we can rule out a simple epoch update FUBAR.
This leaves the other semi regular source of WMM errors - programmers that don't like FORTRAN (esp. super opaque single letter variable 25th degree spherical harmonic functions that date from the 1960s) and feel the need to "do it better".
Having barely survived the prior epoch update and knowing that another will happen again, they carve out some space to build a better mousetrap so that next time will be easier.
This is often a, uhh, interesting intersection of ego and hubris.
And those lines won't be even remotely straight =)
"Why aviation’s compass is shifting towards True navigation"
https://news.ycombinator.com/item?id=28985745
Summary: "The debate about changing from Magnetic to True navigation is now moving towards how to change, and when, with March 2030 as the proposed date."
This NavCanada presentation - gives a good overview of the issues in changing.
https://www.navcanada.ca/en/magnetic-north-vs-true-north.pdf
We have a good (excellent) idea of the density of the core. We also have an excellent idea of how density changes with pressure. Add in that the core must be magnetic and a fairly common isotope in the universe, and you're pretty much left with Fe.