Plans to shift aviation from magnetic navigation to true navigation | Hacker News Reader

Plans to shift aviation from magnetic navigation to true navigation

flightglobal.com

262 pointstankenmate162 comments

With how much the military has been practicing for situations where GNSS will be jammed in the past few years it seems... overly optimistic to coerce the entire industry to ditch the magnetic compass at this point.

https://www.thedrive.com/the-war-zone/17987/usaf-is-jamming-...

https://www.thedrive.com/the-war-zone/15194/russia-jammed-ph...

FAA issued NOTAMs (Notices To Airmen) reveal a lot of deliberate GNSS jamming across the US around military bases, it's not just limited to the Nelis area: https://notaminfo.com/explain?id=1630592

Also Russia enjoys just messing with GPS to annoy NATO exercises, so you never know when you might fly through an area of active GNSS denial: https://www.ofcom.org.uk/spectrum/information/gps-jamming-ex...

Magnetic variation can be pretty dramatic, especially at latitudes past the tropics. It's reasonable to use a combination of magnetic compass with dead reckoning.

And ever changing - drift is quite visible over a decade or so, and using old maps can cause real problems if you’re only using magnetic when you get even as far north as Seattle.

And this is why when doing any sort of navigation activity you should always check the publish dates on your maps/charts and act accordingly!

Don't some maps actually show the current rate of change? I seem to remember some of the USGS maps I purchased showed this.

You're right that they do often show the local magnetic declination's rate of change (around the time of publishing), but even that goes out of date eventually. For relatively short periods (maybe on the order of years or possibly even a decade or two, depending on the particular location), applying this rate of change may give a good approximation of the present day's magnetic declination value, but beyond that the errors can become unacceptably large.

My uncle was a private pilot. He used to take me flying from time to time.

I remember him saying that it's legal to fly without a map, but it's not legal to fly with an outdated map. If you have a map, it must be up-to-date.

I mean the article mentions that GA (General Aviation) has pretty much adopted GNSS at this point. And its likely that airliners can afford the cost of INS as a backup system along with the other backup mechanisms mentioned in the article.

"Today, however, navigation by global navigation satellite systems (GNSS) – backed up by ring laser gyro-stabilised INS/attitude and heading reference system platforms, radio beacons and air traffic control surveillance using multiple technologies – means that aviation has no real need to use a magnetic reference."

Lastly, I would imagine the inclusion of AHRS systems as backup still supports a mission critical VFR/IFR type of flight.

In the event of GPS jamming, I doubt non-critical operations would operate given the heightened risks.

As context: aviators have at least five references that (in reasonably-populated and infrastructure-supported areas) they can usually use:

* GNSS

* compass

* VOR (ground radio beacons emitting a patterned signal to point to where the beacon is)

* Visual landmarks

* Asking air traffic control where radar spots them to be

The meat of this planned change, IIUC, is that maps that have to change to account for shifts in magnetic north over time will now be static, and instead additional offsets to correct the true north / magnetic north error will need to be factored in when an aviator uses one of their five common navigational aids. This seems like a reasonable place to put the costs.

Not just maps, but also runway number repainting and all associated documentation.

NDB (non directional beacon) is also still in use in quite a few places. With two beacons in reach and a bit of math, you can cross reference your position.

Flying as a GA pilot in Montana, I can't rely on VOR for two reasons: signal interference from terrain and the fact that the FAA is actively decommissioning the VOR system. I can't rely on ATC radar because of terrain, either.

Don't forget (if you're VFR): Your eyeballs looking out the window. My instructor would pull the circuit breaker on the GPS if I looked at it too often, to encourage me to always be actually looking outside of the aircraft for ground reference points and point them out on the paper chart.

Sounds familiar! Mine would turn the contrast on the G1000 to zero if I was chasing the needles again :) Bad habit I picked up from simulators.

I doubt we'll lose the magnetic compass tbh... but the idea is that we would use true north for everything. If you needed to use your magnetic compass because your GPS is INOP you'd just apply the appropriate declination + compass card correction then.

In practice, most GA pilots have at least a VFR GPS on the plane and the majority fly with iPads w/ Foreflight now. You put one of those window-mounted ADS-B receivers and you even get traffic alerts and <1m accuracy. For IFR, pretty much all approaches are VNAV and use GPS now anyways.

And how much do they change while flying from LA to NYC? Or on medium distance trips? Or out over one of the owns.

Having to recalibrate continuously during a flight seems very counterproductive. Especially if you drift off course and so can't recalibrate accurately.

The HI needs to be adjusted continuously during flight (every 15 minutes is a rule of thumb but more if maneuvering) anyway. Having to factor in the variation when doing so doesn't seem like a significant increase in workload, and the industry will quickly start producing aids to doing so.

I think they're saying in the extreme event of needing to do declination manually you are safe and can navigate and land the plane, not that it would be a normal occurrence. The default would be using true North and all the modern navigation equipment.

On an LAX to JFK trip, magnetic variation changes from 12E to 13W, or about 1º per 100 miles. In a case of falling back to magnetic navigation from a GPS/INS failure, this would represent an insignificant increase in workload (on that trip; around the magnetic poles, it's higher workload, but it's already higher workload to do magnetic navigation very near the poles).

Many commercial craft already use RLG as a backup to GNSS, and as TFA notes, the maritime industry switched to using mechanical gyro-compasses a long time ago.

Then you can use a compass and use your magnetic look-up table in the other direction.

And only airplanes would then have to use look-up tables. Things on the ground would keep using true north.

This is really fascinating, but probably something that is needed. If nothing else it means airports will stop needing to re-paint their runways periodically. Tampa had to repaint runways in 2011, Stansted had to do it in 2009 and thinks they’ll need to do it again in 2055 [0].

Of course, to get there we’ll have to repaint a lot of runways and replace a lot of signage for runways that currently correspond to magnetic north.

[0]: https://phys.org/news/2011-01-tampa-airport-runways-renumber...

> If nothing else it means airports will stop needing to re-paint their runways periodically.

Airports have to repaint their runways far more frequently than the multi-decade timespan it takes to shift 10 degrees due to wear-and-tear, weather, resurfacing, etc.

I'd wager that maintenance repaint (in place) is less costly than repainting at a different location, which requires additional expertise

you do not repaint in different place, you change the numbers at most, because unless you rebuild the runway you're not going to change its axis to which paint marks locations are referenced.

You can’t just arbitrarily change numbers though. Lots of documentation needs to be updated with a number change.

True. But I'd say not as much as people might think, assuming (oops) that people check NOTAMs

It changes regularly, and by significant amounts. Magnetic north can drift 45km to 55km per year, and in the article it was talking about a major airport in Canada, the Calgary airport, where even slightly out of date maps were off by as much as 7°. Source: https://www.ncei.noaa.gov/news/tracking-changes-earth-magnet...

Will it require repainting? Probably not, but the further north you go, the more noticeable even minor drift or fluctuations will be.

While you're at it, please shift to metric! Feet for altitude, nautical miles for distance, statute miles for visibility, metres for runway visual range (most often)...

Take a plane that has a glide ratio of 1:10, say. It's 1 km high. How far can it glide? 10 km.

Now it's 3000 ft high. How far can it glide, in nautical miles?

My mental math told me ~5 nautical miles, I checked and I was off by 0.07. Metric would be nice but most people who have flown can do the rough math in their heads.

Interestingly, glider pilots in metric countries use metric units.

There are a lot of old Cessna-type planes out there in the US (and to a certain extent Canada) that act as the backbone of the pilot training pipeline: what will it take to update all of those? (And a whole bunch are owned 'for fun'.)

I guess after people had to pay to meet the FAA's ADS-B mandate, this is another equipment update that will need to dealt with.

>I guess after people had to pay to meet the FAA's ADS-B mandate, this is another equipment update that will need to dealt with.

Have us Canucks even done ADS-B? The USA is way ahead of us on that one.

"Meanwhile, the ADS-B mandate in Canada has been under an indefinite suspension since November 2019. It was originally slated to begin in February 2021 but was placed on hold in response to stakeholder feedback."

https://www.ainonline.com/aviation-news/business-aviation/20...

Thanks, couldn't find anything. I knew that happened years ago and didn't hear much.

IIRC a major sticking point was "antenna diversity": in addition to having something point down, Nav Canada wanted antennas pointing up for space-based ADS-B (NavCanada was an initial investor in Aireon).

But the extra antenna is still a bit pricey, but given Canada's vastness, satellites were the only way to get good overage outside of major urban areas.

NavCanada/Aireon would also be using 1090ES and not the UAT that the US allows for lower-flying GA planes as well.

However, if you're near the US border, your transponder can (IIRC) broadcast that you have an UAT receiver on-board (even if you have an 1090 transmitter), and the FAA's gear may send out UAT data (e.g., weather, UAT planes).

* https://skiesmag.com/features/diversity-matters-canadas-perf...

The direction indicator is gyro based rather than magnetic so for most GA it would probably be enough to just learn the offset for the area you are flying and add that when you set/check the DI.

For VFR flying it hardly matters anyway

The direction indicator is not a gyrocompass, though – it will eventually drift unless it's periodically adjusted.

Sure but in small GA planes you're not likely to be travelling so far that the magnetic declination is significantly different so just keep it in mind each time you reset the DI. Or if you are travelling long distance you could make a note of it along your planned route, or your GPS app could let you know.

My point was that this shouldn't require any instrument upgrades to the GA fleet

Also, the compass used for calibrating the gyro is pretty small and wobbly. I really doubt you'd be even be able to read that minor difference off it.

Edit: Just read here that in the pacific Northwest of the US there is a 20 degree deviation! I had no idea. Where I flew it was a degree at most.

I don't have a pilot license, but from what I recall of limited training, don't you do most of your training based on Heading Indicator? You adjust it at beginning, which can easily be switched to whatever heading/offset of the runway is (true or magnetic); then reset it to compass as needed on level flight - which is rare during short training flights, and could be adjusted to appropriate offset.

So I don't think training itself will be a problem.

Once you have actual flights in those aircraft though, I imagine it'll be a bigger kerfuffle for pilots.

a lot of smaller planes have only magnetic compass, no gyro-based heading indicator

Not true, even the lowly rental C172 with 3 shades of paint and carpet at any raggedy flight school will have a gyro based indicator.

Magnetic course calculation is only taught at the initial license level and to instructors. Anyone else is flying by GPS or radio-based nav.

OK but the vacuum gyro in said raggedy-ass 172 needs setting against something as part of the checklist (and quite possibly in flight), which today is the magnetic compass.

Yeah, but this is really only applicable to VFR-only airplanes (mostly trainers). I doubt there are many people really traveling in airplanes without any sort of precision nav equipment.

Practically, it doesn't matter which direction the gyro points as long as you are receiving a VOR signal or GPS signal on a VFR flight.

And yeah, a lot in flight. By definition those gyros are gonna be old, and they cost more to overhaul than they're worth so people who are too cheap to go buy an electronic replacement replace used for used off of eBay or the local radio shop's junk shelf. They're not gonna be reliable, at all.

But, for VFR purposes it doesn't matter and for IFR purposes you shouldn't be flying such an airplane with such equipment IFR anyway, so...

Right. And then you'd have to apply a correction (which might change a tiny bit over several hundreds of miles flown, or over the years).

But no need to change anything in the aircraft, as far as I can tell. Just planning and procedures.

Great, C172 counts as "more expensive" option here, training will go on raggedy ass C150 recovered from a crash, be happy if you get turn indicator.

That in the US?

Here in Europe both are needed to be kept to pretty high standards. You can do basically nothing yourself anymore.

No, in Europe.

There's surprising amount of what is actually allowed and what is believed to be allowed often doesn't match :)

Most GA planes in Poland would be VFR only, I bet.

They just said "a lot of". There are a lot of pre-1950 planes out there flying without a 6 pack to be heard of. Good ole stick and rudder flying. No gyro instruments needed... just altimeter, airspeed, tach, fuel, and the horizon.

NBC: Harrison Ford Lands On Taxiway

https://www.avweb.com/news/nbc-harrison-ford-lands-on-taxiwa...

While it’s legal under part 91 to have only a magnetic compass, a vaccine powered gyro DI (or solid state equivalent) can be found in the majority of the GA fleet. The aircraft without a DI are typically ones with bush flying or acrobatic missions, where pilots don’t spend much time looking at their instruments for navigation anyway.

It took me a while to realize that you meant vacuum powered. :)

Q up there made a Freudian slip :-)

In my country (Romania) all of the small planes I flied (about a dozen) had just 2 or 3 magnetic compasses. These planes are allowed to fly only on visual orientation conditions (weird local laws), so navigation is not a real concern.

I think any requirement to have gyroscope-based instruments only comes in with IFR (at the very least you need turn indicator due to lack of horizon reference).

It's not any weird local laws, it's common aviation laws :) though navigation is a big thing even in VFR ;)

The weird local law is that small planes are not allowed to fly IFR even if they are equipped for that and the pilot is rated. These planes are not even allowed to fly above a low-level cloud with partial coverage.

...a Raspberry PI, some COTS sensors, a USB power bank and an old iPad:

http://stratux.me/

(or: less than the cost of a usual 100h overhaul ;-)

source: PPL applicant and fellow hacker

Doesn't that need to be FAA certified to be relied upon in an aircraft? That's generally what adds all the expense between "homebrew" and "commercial", isn't it?

It needs to be certified to be permanently installed in a non-experimental aircraft, or to be relied upon for IFR use, but for VFR use powered from a cigarette lighter and suction cuped to the window, you can do whatever you want.

It's classed as "pilot carry-on" equipment and doesn't need to be certified. Only stuff permanently installed gets that treatment.

Just as I don't have to have my pen and pad (or indeed my iPad) certified either :)

I wonder how many aviate with a big-ass “portable” lithium ion battery to power it all instead of paying $100 for a flight-certified cigarette lighter receptacle:

https://www.aircraftspruce.com/catalog/elpages/cigrecept.php

I have a pair of 13aH Anker batteries I use, rather than dealing with the lighter plug. The electrical isolation is a feature.

uh, no.

Homebrew hacking is one thing on your dining room table, or for basic home automation, or whatever.

Homebrew hacking in an airplane sounds like an awful idea.

why?

homebrew solutions generally don't have the excessive redundancy that keeps planes from crashing.

You mainly see "excessive redundancy" in larger cargo, passenger, and military aircraft. Small general aviation airplanes don't have as many redundant systems as you'd think. There is neither the space or weight budget. For safety, they mainly rely on well engineered systems, frequent inspections, required maintenance and updates, and failsafe design, such as the ability to pilot the plane as a glider if the engine cuts out.

Not all systems are safety-critical though. Most hackers probably wouldn't mess with control surfaces, engine control, and instruments, and would err on the side of safety too. But planes don't immediately drop from the sky just because their radio is off or their navigation systems have a hickup.

Homebrew hacking of ultralight airplanes (including homebuilt planes) is common here in Czechia, legislation is much less restrictive than for homebrew hacking of cars.

> Homebrew hacking in an airplane sounds like an awful idea.

These are not for commercial aviation. The only area where homebrew can "fly" is experimental airplanes. And in that application it kinda makes sense. Many of those airplanes were made in someones garage themselves, so why stop there and why not make the instruments yourself too?

Uh, yes.

There is a whole aviation subculture of experimental aircraft designers, builders, and hobbyist engineers. There are limitations of course (mostly to do with passenger safety) but the FAA grants a surprising amount of leeway once an aircraft is granted the "experimental" label.

A lot of those are also being retrofitted with newer gauges... Garmin has a whole series of products that is basically "take your six-pack and make it digital!" sort of stuff. I think your ADS-B analogy is spot on -- I'd imagine this go somewhere in the same way as that.

> this is another equipment update that will need to dealt with.

Even in planes with only 'steam' gauges the changes are minor — you won't need any new equipment.

Currently: direction indicator is set to magnetic. When planning a flight you take true headings from charts and have to convert them all to magnetic. You then fly magnetic headings.

After the changeover: direction indicator is set to true. No need to convert headings when planning a flight. You fly true headings, and the only conversion you need to make is when setting the DI from the compass.

(If you don't have a DI you can still pre-convert all your headings to magnetic and fly those. You'll need to mentally convert runways headings etc. though.)

It drifts considerably over time so you'd have to set it to true periodically which on the ground during start up is fine but not in the air, having to determine magnetic variation at your current location.

magnetic variation doesn't change all that quickly at 100 knots, and charts provide the variation. I don't really see it being a much bigger workload, and I imagine that if this change does occur chart plotters like Foreflight will start displaying the current variation very prominently for convenience (it's already pretty easy to pull up). I can also imagine people starting to sell retrofit bug rings for heading indicators that let you set the variation in for convenient setting.

But in general most pilots of slow aircraft probably already know the approx. variation around their area by memory, most pilots of fast aircraft will have instruments that do it for them.

Its kind of funny. In our initial training the FAA requires that instructors really drill it into our heads when we using magnetic vs true numbers then as soon as you pass your first check ride you basically never think about it again.

I've been flying since 2013 with almost 500 hours at this point. I could make some educated guesses about where we use true vs magnetic, but aside from runway designations couldn't tell you much for certain.

Its never come up in my flying.

CFI here. It’s not a big deal in most of the country but the Pacific Northwest does have variation of about 20 degrees. It can make a difference when calculating takeoff and landing data as winds are true but runways are magnetic.

I think it’s important to point out the nuance. Observational winds (eg METAR) are recorded in true. Reported winds (ATIS, ASOS, AWOS) are given in magnetic. [1]

The adage goes “If you read it, it’s true. If you heard it, it’s magnetic.”

[1] https://www.faa.gov/documentLibrary/media/Order/7900_5D.pdf Chapter 7.4

What if you read the ATIS though? /s

one of my favorite apocryphal exchanges:

airplane inbound to land: "KXYZ tower, N12345 at 3000' tower: "N12345, KXYZ tower, confirm you have Romeo" airplane: "KXYZ tower, N12345 has Romeo" tower: "N12345, fine, but bravo is current, recommend you recheck atis"

Oh you must have meant KDTW.

When I was working on FMS, that's what we used to test our true north to mag conversions. Just fly across the Pacific Northwest and toggle the switch to verify that everything looks good.

Related to this topic, here's an interesting NOAA site with more details about Earth's magnetic declination and containing lots of data about how it changes spatially and temporally: https://ngdc.noaa.gov/geomag/declination.shtml

They even have detailed data for predictions about how it is likely to change in the coming years (presently up until the year 2025).

> They even have detailed data for predictions about how it is likely to change in the coming years (presently up until the year 2025).

They have been publishing the models in 5-year packages for as long as I can remember (e.g. previous one was 2015-2020 model, and so forth). I still have 30 year old devices/PDAs/GPSs that see firmware updates just for the magnetic declination models.

Curious how they do it these days, since all these devices with a compass need these up-to-date models. Likely they just phone home every time. :(

It probably depends on the specific application, but I would imagine the models/data that various devices in the field are using are probably updated as part of some periodic maintenance schedule. They don't change significantly enough or quickly enough to demand online updates that frequently, but I suppose every device manufacturer/maintainer has their own way of doing it for whatever reasons they might have.

In my own work, I've downloaded the dataset from NOAA and their tools to parse and work with this data to generate my own global 1-degree by 1-degree by 1-year "grid" for magnetic declination [0], along with some code [1] to read this data and be able to give you an estimated value for magnetic declination for any position on the globe for any time instant between 2020 and 2025. Before 2025, I will probably need to download the new data, run the tools again, and update my own dataset (to include values for 2025-2030 or whatever the case may be), but this will definitely be a manual process.

[0] https://github.com/ls4096/sailnavsim-core/blob/master/compas...

[1] https://github.com/ls4096/libproteus/blob/v0.6.2/include/pro...

Kinda funny that the aviation industry cannot implement the more accurate inertial navigation systems (INS) right now because:

"The biggest single problem in trying to implement this change worldwide would be inertia"

INS that doesn't drift pretty much immediately is expensive and needs periodic fixups, and the moment GPS became available it pretty much dropped off anyones purchase plans (as it can't be used as backup for GPS unlike VOR/DME)

I think they may have been joking since INS - is inertial navigation.

While INS is not simple, it's also not that difficult to implement. As even the cheapest drones that can hover show new MEMS sensors are accurate enough to work with a proper filtering.

I did some prototype INS system as my master's thesis 10 years ago, the code was quick and dirty and even then the accuracy was like 30 meters after an hour of walking around with the device.

Thing is, it has to work over atlantic/pacific/cross north pole routes, etc. We're talking multiple hours and long distance, possibly with a lot of turbulence (even for GA, which actually gets less steady flight so...).

And then it needs to provide guarantees about said navigation, guarantees that those drones do not need.

That is surprising, you must have had an extremely accurate accelerometer and gyro, or employed tricks [1]. There are two problems with determining position from acceleration measurements:

1. You're integrating twice (acceleration to obtain velocity, then velocity to obtain position). So if you have any noise or error, you're integrating that, and integrate that again. Hello, parabola.

2. Gravity. It's strong. So you have to subtract it (as it induces an apparent acceleration upwards).

If the difference between actual down and where your model thinks is down is just a fraction of a degree, you'll be totally off within minutes.

See eg here: https://www.youtube.com/watch?v=C7JQ7Rpwn2k&t=1401s

Or here: https://www.cl.cam.ac.uk//techreports/UCAM-CL-TR-696.pdf

> As a concrete example consider a tilt error of just 0.05 [degrees]. This error will cause a component of the acceleration due to gravity with magnitude 0.0086 m/s2 to be projected onto the horizontal axes. This residual bias causes an error in the horizontal position which grows quadratically to 7.7 m after only 30 seconds [and thus to 770 m after 5 minutes, unless I'm mistaken, and 110 km after an hour]

Or here: https://liqul.github.io/blog/assets/rotation.pdf (search for "Accuracy of Velocity and Position Estimates").

[1] such as assuming that your foot has velocity zero while on the ground, which does not hold when you're in an elevator, for example, and which you can't use in a drone without some serious sensor fusion.

I had 2 tricks - really high-order filter borrowed from some paper and the assumption that a walking human doesn't gain constant acceleration. Even in an elevator you stop on a floor which resets your speed to 0.

I agree that there is no way you could extend this directly for flying, but with modern devices and things like ground-distance radar, relative airspeed indicators and so on I don't think it is beyond the realm of possibility. Plus we have detailed hightmap of the world, which, when combined with a radar should allow for terrain tracking. That makes the accuracy of sole INS much less crucial.

This also depends on the plane. For larger commercial applications, you need to have INS. You want to use a combination of sources ideally, since INS is accurate for a shorter period and GNSS/GPS for longer periods(often GPS/GNSS is only updated every second). Plus a lot of newer units have a much smaller drift. This FOG has a drift of 0.1 deg per hour, which is quite good (https://www.advancednavigation.com/solutions/spatial-fog-dua...).

Outside of military uses when GNSS can be jammed INS is pointless when GNSS is available.

INS that is accurate is very expensive to build and maintain. INS that isn’t reliant on external inputs including from a magnetic compass for calibration is even more so.

And even top-grade military INS does external checkpoints where possible (although it's probably pretty accurate in any case).

Not saying you're wrong, but. . . who actually knows what actual top-grade INS is doing these days? Those kinds of capabilities would probably be Top Secret or SCI.

The SR71 was using stars to navigate!

You need clear view of the sky and big lenses (you can always use more compact metamaterial lenses and infrared imaging for cloudy days but they are as expensive if not more than INS). Star charts also drift over the years and you will have the same problem as magnetic true north where the database needs to be updated regularly. Fine for airliners, not so great for skyhawks.

Yeah I guess that wouldn’t work during takeoff and landing. But for the most common airliners (a320 to a380 and boeing equivalent): are there clouds above their cruising altitude? By day I presume you could use the sun.

Some early jetliners had special cupola for star navigation, but it soon fell out of use because NDB, VOR, DME and other radio systems were easier and better.

I'm imagining a navigation system by trying to pattern-match the earth terrain with a downward-facing camera from the plane.

A suitably large database of satellite photos covering various conditions, day, night might work for all cases but cloudy (when the plane is above/in the clouds).

Already exists: https://en.wikipedia.org/wiki/TERCOM Since the 1950s!

Oh yeah, contour-matching. I remember this being touted with regard to U.S. cruise missiles in the 80's, 90's.

Guess radar + countour is more reliable than camera + imagery.

(I'll crawl back to the 1800's now.)

They've used that landing on Mars as well, Terrain Relative Navigation.

An automatic celestial navigation system for navigating both night and day by observation of K-band or H-band infrared light from multiple stars.

https://patents.google.com/patent/US7349803B2/en

In this celestial map, the bodies of the solar system are placed so exactly that those versed in astronomy could calculate the precession (progressively earlier occurrence) of the Pole Star for approximately the next 14,000 years. Conversely, future generations could look upon this monument and determine, if no other means were available, the exact date on which Hoover Dam was dedicated.

https://www.usbr.gov/lc/hooverdam/history/essays/artwork.htm...

That worked in the SR71's case because, flying high as it did, the sky above is black and you can see stars during the day.

They were teaching cadets at the Air Force Academy celestial navigation in the 1980s.

This guy

https://en.wikipedia.org/wiki/Guy_Murchie

taught celestial navigation to navigators flying across the Atlantic in WWII.

Exactly what I was thinking about:

https://www.thedrive.com/the-war-zone/17207/sr-71s-r2-d2-cou...

https://www.thedrive.com/the-war-zone/41287/r2-d2-spotted-on...

If something unforeseen happens an the GNSS systems go down for whatever reason we might be set up for a terrifying few months of disruption. Coronavirus was bad enough, and most of the disruptions were voluntary to some extent.

We still have VOR network and other legacy systems. Some are no longer integrated into parts of the avionics but you can still plan routes and use them to fly. Plus Primary Surveillance Radar will see you anyway.

I wonder how long it will take to get the VOR network serviceable. Many of them are no longer maintained.

some dropped off maintenance, but not all. NDB is pretty much dead outside of few rare spots, though, and not everywhere had DME even at best time. But nav points used with GPS still often are based on VOR locations.

If all the various GNSS constellations went down simultaneously we'd definitely be in the shit. Not just because we lost GNSS, but we'd also probably be fighting a war or Kessler syndrome would be in effect. Either way, losing GNSS would be just one of many problems!

Operation Black Buck [1] was done using INS [2] as GNSS was not yet available.

[1] https://en.wikipedia.org/wiki/Operation_Black_Buck [2] https://en.wikipedia.org/wiki/Delco_Carousel

I wonder if someone got intel that we are about to have a pole reversal or it might stop working completely.

Awe man, they just moved the runways at my local airport a couple years ago to align with the newer magnetic north. It used to be 18/36 and 9/27. After the move it's 1/19 and 10/28.

Neat article, but I have a question that's kind of a tangent: what are those rose-colored lenses that the pilots have flipped down to look through the windshield of the plane in the picture?

A heads-up display: https://www.flyingmag.com/how-it-works-head-up-display/

My first guess would be heads-up displays. On photos they always appear blank.

As a GA pilot, one of the complications of the navigation exams for small planes was navigation and calculation of magnetic versus true and the entire range of derivations. It was mostly useless because of the local legislation demand to fly only in visual conditions (IFR not allowed for small planes), but it made the exams unnecessarily harder. The ever worse part was the demand to be able to calculate a flight path to something like New York, where Earth curvature matters, for planes that cannot fly more than 1000km at low altitude and speed, so they are never allowed to fly over the ocean or on distances big enough to have a significant difference between a straight line on the map and the shortest route. I am happy to see at least one of these going away, even in 9 years.

I have some training as a VFR pilot (for ultralight aircraft). I was under the impression that true north was always used everywhere (maps mainly), and adjusted with the local (and current) magnetic deviation when preparing the flight plan, to be able to take accurate bearings.

Using magnetic north in maps and databases seems... misguided. Not updating instruments with the latest value too, although it must be a lot more complex to do so over long flights, with non-negligible deviation changes.

Don't lose your bearings! I can imagine it's easy to rely too much on instruments when they're available.

What is the advantage though? True North is of course easier to understand and use when navigating manually, but what's the benefit in a commercial airliner?

TFA doesn't precisely enumerate them but two I saw were:

* removes the ongoing process / cost of updating mag tracks as the Earth's magnetic field shifts

* avoids errors that occur when the true/mag difference is correctly specified

It removes the need to maintain the lookup tables that are used to compute magnetic north from the true north determined by the navigation system.

I don't know anything about them, but looking it up, apparently inertial navigation systems can determine true north by sensing the spin axis of the planet! So it isn't just a 'gps is easier' kind of thing.

There are two main ones 1. modern navigation systems often work in true North already but have to map to magnetic for display & to match charts. 2. magnetic north moves! This greatly complicates how you deal with the first point.

I don’t envy the Canadian pilots they were talking about who tested some of this current stuff, and found their plane’s idea of the runway direction way very different from where it lay.

First Air Flight 6560 crash [0]

[0] https://en.wikipedia.org/wiki/First_Air_Flight_6560

PS: I highly recommend crash analysis written by Admiral Cloudberg. In the above case: [0] Arctic Approach: The crash of First Air flight 6560

[0] https://admiralcloudberg.medium.com/arctic-approach-the-cras...

> What is the advantage

From the article:

“The migration of the geographic magnetic poles has accelerated in recent years, adding to the relentless task of updating systems and distributing the associated flight information.

The AHRTAG points out that updating aircraft declination look-up tables is a specialist and expensive maintenance activity that has no effect on the way an aircraft derives its directional information. It merely ensures the result is displayed as a magnetic value that is normally less accurate than the originally determined True heading.

And, if a future variation shift is sufficient to affect airport assets – like runway and taxiway signage and markings, plus instrument procedures, landing aids documentation, and FMS coding – at a major hub, the cost can top $20-30 million.”

https://www.flightglobal.com/flight-international/why-aviati...

That last paragraph makes sense, changing taxi markings etc is inherently expensive. The lookup tables part is harder to understand, but perhaps the airplane software is very badly written.

It's a fundamental principle thing, that has some knock-on practical effects. Navigation is fundamentally getting from point A to point B. To do that, you steer a course between the two. Do you want to describe the angle of that course in reference to

(a) A fixed line that never moves, such that the angle ('bearing') of that course is always the same

(b) A line that moves around, seemingly randomly, particularly if you are near one of the poles of our planet

Obviously from first principles, you'd pick the first. Due to historical navigation technology it was more convenient to use the second though. We had an instrument (magnetic compass) that would directly give us reference for (b), and so we described everything in those terms, and maintained tables of offsets so that we could calculate (a).

Using (b) - magnetic North - causes some problems and because very few aircraft, and no commercial ones, rely on magnetic bearings as a primary source of navigation those problems are not worth it. One of the problems comes when you start labelling things that are fixed relative to (a), because they're attached to the ground but you label them using (b). After a few years the labelling is wrong and they need relabelling. This requires everything from pointing of radio beacons to repainting runways. It's all needed for effectively historical reasons.

There are two Norths:

The one that points in a constant direction on the Earth's surface. Getting from point A to point B on the Earth is fundamentally what navigation is and so having a fixed reference for that is good (modulo continental drift).

The direction that a magnetic compass points. This is at an arbitrary and changing offset to any direction on the Earth's surface.

Why

Now I get it, using the magnetic north is akin to the daylight saving time kerfuffle, on steroids - you basically have to account for variations even during the same flight if you fly near the poles.

The magnetic north is even affected by local phenomena, at least when you're on the ground, so it's worse than that.

> (a) A fixed line that never moves, such that the angle ('bearing') of that course is always the same

Just to nit-pick your otherwise great comment: This may be true for short, general aviation navigation, but long haul airliners typically navigate via great circle routes, which do change true course throughout the route.

Yes, there's lots of reasons why you don't fly in a straight line from airfield A to airfield B. Whether that's a great circle or just a multi segment line to avoid an airspace restriction I suppose what I was really talking about was "your bearing at any given moment on your course".

I'm aware of all this, it's the same in sailing and it's a mess. But since aircraft are already set up to use magnetic north, and are basically flying computers, it shouldn't matter what crazy navigation scheme they are using.

But a sibling comment already pointed out, what you also mention, that it also affects physical markings etc, and that makes much more sense.

IIRC, non-uniform magnetic variation in northwest New Mexico: not aliens or jamming. Just some differences in composition of the Earth around there.

In addition to the drift of magnetic north, it's important to keep in mind that there are local variations. These are indicated on aeronautical charts but take some getting used to.

> While professional mariners stopped using the earth’s magnetic field as their primary directional reference some 50 years ago, civil aviation did not, because at that time accurate inertial navigation systems (INS) were too heavy and bulky for aircraft use.

Ships do not sink if they get lost with no fuel.

The article mentions that the magnetic field of the earth is changing more rapidly. Why is that?

It goes through cycles naturally and from time to time the magnetic poles flip (it happens every few hundred thousand years). The magnetic field is largely created by the movement of molten iron and nickel in the earth's outer core. Wikipedia has a pretty good article on it.[0]

[0] https://en.wikipedia.org/wiki/Earth's_magnetic_field

Whoa it looks like we're estimating it takes ~7000 years for it to complete the flip.

https://www.nsf.gov/news/news_summ.jsp?cntn_id=100358

Biology appears to survive it but I'm curious what happens to our digital ecosystem when we lose a portion of our protection against charged particles.

No one knows. We just observe it happening.

>> The article mentions that the magnetic field of the earth is changing more rapidly. Why is that?

It is heading toward Russia. Putin is a super villain and he's stealing the north pole.

I prefer Right navigation :P https://en.wikipedia.org/wiki/Magnetic_declination

GPS goes down or is spoofed or blocked, a solar storm hits, software bugs & crashes, how many RISKS to the public ?

GPS is not involved in this change really. Solar storms affect the magnetic field of earth to. Magnetic north is just a sensor going through software like everything else. Less risk... not more.

Er... I get it that it's about changing the "reference system" and not primarily about GPS. But the difference between "magnetic North" and "true North" depends on your position, and how are you going to get your position if not using GPS?

Using a wide variety of "traditional" techniques that range from dead reckoning (or "pilotage" which is dead reckoning corrected by landmarks) to politely asking a controller if they have you on radar. Airplanes operated under challenging conditions without falling out of the sky for a long time before GPS became a ubiquitous flight instrument (pretty recently, really).

> GPS is not involved in this change really.

How do you determine true north without a GPS system?

Wouldn't it be possible to broadcast local magnetic declination over ATIS or other automated broadcast systems?

As far as I know (and according to the article), modern navigation systems contain databases of the local magnetic declination anyway; instead of updating maps and navigational databases, we could just update these declination database instead every once in a while if I understand it correctly.

How do you apply these things without knowing where you are?

True/magnetic deviation is localised. You need to know where you are to know what the localised value is.

Wouldn't a very rough location suffice, i.e. something that could be either manually set (for general aviation and shorter distances), derived from a VOR station identifier or similar, or just estimated via dead reckoning/an INS?

In other words, if you don't even have a rough idea of where you are, what good will a magnetic heading do?

Rough yeah - but I think it does change by integer degrees from actual map sheet to map sheet, so you could probably drift a couple of degrees without knowing it within an hour or so of flying.

How do you determine true north with a GPS system? GPS only gives you your position, not your orientation.

> How do you determine true north with a GPS system?

  def true_bearing(magnetic_bearing, location)
    magnetic_bearing + gma(location)
  end

And that's the point - your true bearing is a function of your location.

Ah. Right. Duh. (I must be having an even worse day than I thought.)

Magnetic declination and deviation are already trained concepts in nautical navigation. Don't see why they couldn't be used with aeroplanes as well. Bit more calculating, but not really very big deal.

They already are; every private pilot is trained on magnetic variation and deviation as well as magnetic dip (turning) and acceleration errors.

> GPS goes down or is spoofed or blocked, a solar storm hits, software bugs & crashes, how many RISKS to the public

None. The second sentence in the article:

“…navigation by global navigation satellite systems (GNSS) – backed up by ring laser gyro-stabilised INS/attitude and heading reference system platforms, radio beacons and air traffic control surveillance using multiple technologies.”

https://www.flightglobal.com/flight-international/why-aviati...

The FAA is also maintaining a core set of ground navigational based stations (VOR) in case of GPS failures. It’s the COBOL of the aviation industry :) There are occasionally parts of the sky that have GPS outages due to military activity anyway.

Just more money for the avionics shops

OT: looking at the maps on FlightAware, Flightradar24, and similar sites and seeing the vast number of planes crisscrossing the US at any one time I wonder if it would be possible to do a peer to peer navigation system?

A plane at 30k feet should have line of sight to any other plane within about 200 miles, and even farther the higher up the other plane is. If the other plane is at 30k feet, it should be in line of sight at about 400 miles.

Have a way for planes to exchange information with other planes that are in of sight about where they are heading and how confident they are that they are on the right heading.

So let us say you've got a plane flying from Los Angeles to New York. You see what other planes you can see. That should include others that are going to New York but are ahead of yours. Find out from those who confident they are that they are on course, and use that to figure out a good course for you to follow and an estimate of how confident you are in that course.

You in turn provide your course information to other planes heading to New York that are behind you.

I think you could probably make a viable system with omnidirectional transmitters on planes for broadcasting course and confidence information, and directional receivers for receiving those broadcasts.

I've sometimes wondered if some whales use a system like this. I remember reading once about some species of whale (I totally have forgotten which species and even where they lived) that had a long annual migration. Researchers had attached GPS trackers to several of the whales and recorded their routes.

The researchers were surprised by how direct the routes were. The various ways they had hypothesized that the whales might navigate would have enough uncertainty that they expect the routes to have a lot more deviation from the direct route.

The number of whales they attached trackers to was only a small fraction of the number of whales in the migration, and from what I read the migration doesn't start all at once. As the weather turns more and more whales start the migration.

Suppose the whales navigate like I suggested above for planes. The whales that leave early or using the imprecise methods that the researchers hypothesized. They go in the right general direction using clues like sun position, but can get quite a ways to the side of the straight route, such as when they lose sight of the sun.

The whales that leave a little latter would do the same thing. But the ones behind would also be able to hear the calls of the ones ahead. If they can tell what direction those are coming from, they can use that as a navigation input. If there are several ahead going toward the average position of the leaders should put the follows on a more direct route.

Even if there is only one ahead that you are following, as long as that one is on average going in the right direction you should end up on a more direct route. That's because if the leader is drifting side to side and you are going toward them which causes you to also drift side to side your drifts should have a smaller amplitude.

Those farther back following you will have even smaller drifts. The ones following your followers will be doing even better, and so on.

If the whales the researchers attached trackers to where all far enough back in the migration, the above mechanism might explain what the researchers saw.

Bad idea. Wouldn’t want to be flying over water in Asia when China decides to invade Taiwan with just GPS.

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