Primarily for general aviation discussion, but other aviation topics are also welcome.
By highfive
#1705286
An interesting and perhaps cautionary tail from NASA.

https://www.gpsworld.com/nasa-report-pa ... isruption/

I haven't worked out what kind of aircraft this was, but I would have thought it had a FMS.

I have long thought that GA GPS units should include some sort of DME input for gross error detection, or even better if a suitable low-cost inertial device could be developed.

What is worrying is that the GPS 'came back online' and was still misreporting position?
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By Flyin'Dutch'
#1705293
The 'resilient navigation and timing' folks who's magazine that article is published in suggest that we have eLoran as back up for GPS.

Would be interesting who is promoting that organisation.
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By Flyin'Dutch'
#1705301
@Paul_Sengupta

I don't deny there are actual threats to GPS but whether LORAN is the way forward or DME, I seriously doubt.
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By FlarePath
#1705311
Out of the Box and Blue Sky thinking alert. Why not convert all those soon to be redundant VOR's to squirt out GPS signals that will will correct any hiccups from outerspace gremlins.

Believe, but can't remember the system that does something similar but my Aera 500 doesn't have the capability to utilise it?

I know satellite systems are really the only way for global nav either land sea or air but couldn't a specific country ground based system work?
By highfive
#1705335
Flyin'Dutch' wrote:The 'resilient navigation and timing' folks who's magazine that article is published in suggest that we have eLoran as back up for GPS.
Would be interesting who is promoting that organisation.


That's true, but it's worth noting that the original report was in NASA's Aviation Safety Reporting System (ASRS) database and was highlighted in last month's issue of their Callback newsletter (although the incident seems to have occurred last August).

https://asrs.arc.nasa.gov/docs/cb/cb_473.pdf

I don't think that I can post a link directly to the report but it can be searched at this link:
https://asrs.arc.nasa.gov/search/database.html. Search by Report Number (ACN) for 1565516.

It looks like the aircraft was a C560XL mid-size bizjet. The report was filed by Salt Lake ATC (centre), and the controller concluded
"Had [R-Side] not noticed, that flight crew and the passengers would be dead. I have no doubt."


The thing that surprises me, is that a reasonably well equipped aircraft can be 'spoofed' in this way, with no mis-compare being flagged either by the system or against INS or DME/DME.

I certainly intend to be more thorough in cross-checking with anything else that is available (DME, NDB) when flying GNSS approaches in future. I know that's plain good airmanship, but freely admit I have been getting a bit too comfortable with GPS of late.
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By Sooty25
#1705413
riverrock wrote:WAAS / EGNOS is the satellite based version. https://en.wikipedia.org/wiki/European_ ... ay_Service
DGPS is the ground based version. https://www.trinityhouse.co.uk/dgps

Both are freely available in the UK (although DGPS broadcast is designed for shipping - not aviation).


I've personally seen instability in positioning with EGNOS capable receivers, albeit at ground level. Deselecting EGNOS then resulting in significantly more stable and accurate positioning.

I've also seen a huge error, 100+ miles, appear at random times in the close vicinity of Sizewell power station, which we put down to jamming.

I guess as the boot screens keep telling us, it's an "aid" to navigation.
By riverrock
#1705450
Sooty25 wrote:
riverrock wrote:WAAS / EGNOS is the satellite based version. https://en.wikipedia.org/wiki/European_ ... ay_Service
DGPS is the ground based version. https://www.trinityhouse.co.uk/dgps

Both are freely available in the UK (although DGPS broadcast is designed for shipping - not aviation).


I've personally seen instability in positioning with EGNOS capable receivers, albeit at ground level. Deselecting EGNOS then resulting in significantly more stable and accurate positioning.

I've also seen a huge error, 100+ miles, appear at random times in the close vicinity of Sizewell power station, which we put down to jamming.

I guess as the boot screens keep telling us, it's an "aid" to navigation.

EGNOS and DGPS only help with atmospheric and satellite issues - they don't help with integrity. RAIM tries to do integrity, by cross checking with other satellites. However as none of the civil data is encrypted it can all be spoofed and jammed.
On the jamming side - I'd have expected a certified GPS to show that GPS was unavailable rather than show entirely the wrong position.
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By defcribed
#1705461
riverrock wrote:On the jamming side - I'd have expected a certified GPS to show that GPS was unavailable rather than show entirely the wrong position.


My understanding is that the aim of jamming is to cause an operator and/or their equipment to be unable to distinguish between genuine and false signals rather than simply to deny usage.

Denying usage is quite crude and something of a last resort. The greatest tactical and strategic benefits arise when an enemy is being jammed but doesn't know it, although the period of time where this is the case for any given technology is often short and must be exploited to the full.

Another plug for the R V Jones book 'Most Secret War' which covers this stuff in fascinating detail.
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By Sooty25
#1705469
EGNOS hasn't been seen to affect integrity, only stability and accuracy. Once upon a time, having your position floating about in a 50mtr footprint was considered wonderful, now everyone demands it within a couple of meters! A floating HDOP an fluctuating Lat/Lon upsets some! I'm familiar with RAIM but it isn't something the average leisure user would find built into their iPad or any App they happen to be running. What chinese produced GPS is certified?

The offset was observed in the GPS tracks recorded in a number of vessels traveling close to shore, up the east coast. None of which were RAIM enabled systems, nor did they throw up any error message. The offset was due east and very localised.
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By PeteSpencer
#1705483
The last time a fairly localised GPS Discruption was promulgated for a week earlier this year around D208/Sculthorpe , I rang the mobile number on the NOTAM on the tuesday morning as our strip was right next to the epicentre.

'Nah mate we finished at 11 this morning: nothing more this week.'

Peter :roll: