I am not sure anyone knows, but I also would like to know that.
I would also like to know if they were fed a static position or they had a position that was moving right along with accurate speed and altitude, but 60 miles over.
I guess we are lucky they weren’t good enough to gradually move the plane over bit by bit, that might have made the crew just think the INS had got drifty.
These are called “corner cases” in software engineering. Every so often you get an error condition no one thought of or a combination of errors no one thought of.
Airbus had one where they disabled the stall warning below a certain speed to keep it from going off while taxiing. What they didn’t realize was that someone would get the plane so slow in flight they would get into that speed range and thus the stall warning would go off every time they sped up.
They probably planned a lot for GPS jamming or other loss of signal, but not much at all over a good but hacked signal. Hindsight is 20/20, but here is how I would do it.
If the GPS and INS diverge more than X miles in Y minutes, do the following:
Switch the autopilot to heading mode.
Display an alarm like “GPS INS DISCREPANCY OVER LIMIT, AUTOPILOT REVERT TO HEADING BUG”, then display the raw GPS position+speed and the raw INS position+speed. The crew can take it from there.
If you want to get fancy, display a graph so you can see one of the two suddenly went nuts.
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The gist I get is the ins drifts a known amount for a postion and direction on the planet, hence an almanac could correct that.
I think thats how subs do it.
A pilot told me NY to UK you are about 6 miles off course on the old INS systems, who cares your in radar range when it matters, but when the sky gets busy maybe not so good.
Oceanic routes out of radar coverage were designed with that level of (in)accuracy in mind. Also note with TCAS and now ADS-B, (flying versions of AIS), the airplanes can see each other when they get close.
Seeing each other is one thing who decides on the next move?
Interesting article here:
INS and GNSS errors are complementary.
GNSS and inertial navigation systems (INS) have complementary error characteristics: GNSS has good long-term accuracy whereas INS has good short term accuracy. INS is self-contained, operates continuously and provides navigation solutions with low short-term noise. However, it suffers from accuracy degradation over time due to the integration of biases and drifts of the inertial measurement units (IMUs).
Some what analogous to celestial and dead reckoning. DRs are low noise but tend to drift over time.
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Normally there shouldn’t be a next move decided by them, ATC is controlling both planes. If you noticed you were gaining on the airplane ahead of you for one example, you would mention it to ATC and you might get told to slow down or the other guy told to speed up. The aircraft can also talk to each other, there is usually a common VHF frequency for the route that has a range of over 100 miles at the altitude they fly besides for overhearing the HF conversations depending on how the SELCAL is set.
Obviously this does not work if you are actually close enough to hit someone, then you do what you need to do. Airplane right-of-way is similar to two power vessels, but at closing speeds that can be over 1,000 knots you don’t have a lot of time to figure it out.
The better versions of TCAS can talk to each other to prevent the two-people-in-a-hallway scenario where you both move into each other’s way. Keep in mind these airplanes over the ocean are flying IFR and having to DIY collision avoidance would mean someone badly screwed up somewhere!
Sunday flying VFR I had someone in my six headed for me and climbing towards me. I could see him on the display, but I can’t see below and behind me visually. Being the overtaken aircraft I had right-of-way and I should have been very visible to the other plane, but I was a bit nervous watching the little symbol creep up on me. They eventually turned and went somewhere else.
One interesting thing in that article is that ships could use INS to assist in detecting spoofing because the INS detects small changes in position that GNSS spoofing would miss, small pitch and roll for example.
yes but by the position and time you are telling them…
Just had a buddy telling me in a 747 freighter, he was catching some Russian tub, just pulled out and passed it, told the controller after they were in front. The russian aircraft was going slower than they reported.
PS pitch and roll compensation built into every DP system, heave is optional
Dp uses that now, when INS coupled, bad gps data same as spoofed when your close to a platform.
Spoofing was considered from the beginning of Navstar.
The extra coded frequency broadcast from Navstar is just the same data, what the industry assumes is the military vessel is getting an almanac from a ground service and comparing to the downloaded so they can know the data is wrong.
Plus the military uses the 2nd frequency to help fix atmospheric issues, all offshore dgps receivers decoded and use this.
Civilians will get this when all the sats change to ones with L5 broadcasts. Will make your phone much more accurate but no defence to spoofing unless the cell towers can send you an alamanc, I bet that service is coming…
Sounds like your buddy was pulling your leg because that ain’t how it works.
over Russia pre ads-b that was only 2020
Like the US C5 that nearly wiped out a Qantas flight as the US plane read the time wrong, in reverse to the area controller, put both aircraft at the same place at the same time instead of an hour apart only saved by the small errors in altimeters.
Back in the gulf war
FYI if you are interested:
Big changes are happening over the North Atlantic, the busiest piece of Oceanic airspace in the world.
Since the 1960s, a system of organized tracks, like a multi-lane highway in the sky, has been in place for any airline wishing to cross from Europe to North America and vice versa.
But the advent of satellite-based tracking of planes, also known as space-based ADS-B, is enabling air traffic controllers, led by the UK NATS, to shake up the Organised Track System (OTS) and even get rid of it entirely on certain days. It’s all part of efforts to help planes fly more efficiently across the Atlantic, saving time, money, fuel and CO2 emissions.
AeroTime spoke to Jacob Young, a former Oceanic controller and supervisor who is now manager operational performance at NATS, about the changes.
“It’s been probably some of the most transformational times that we’ve had since I’ve been at NATS,” Young says. “Space-based ADS-B and the COVID-19 pandemic are the two key drivers that have let us move to OTS nil on certain days.”
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all based on gps, scary
What altitudes do you need ads-b where you are?
Hence you knew other guy has it as well?
I knew the other guy had it because that is how I was “seeing” him, on the screen. Visually I would have never known he was there, I can’t see below and behind me.
There is so much Class B airspace around where I live that ADS-B is very common, if you don’t have it there are huge areas that you couldn’t enter.
You can see the required areas here:
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oh my golly gosh, lost without gps.
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Jammed is one thing, spoofed is another. Imagine fake AIS targets in your way and real ones in your way appearing 50 miles off.