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Comment by dosman33 | Hacker News Reader

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...

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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.

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).

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.

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.

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.

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

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.

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.

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.

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!

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.

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.

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.

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