[Nerds Alert] Use of TIS-B data in en-route RNAV navigation in case of GNSS loss?

[Ibra]

There is an AIC in France where they removed load of VOR, DME, NDB...I was discussing with an ATC on GPS loss procedures (in addition to plans for weight loss in 2024 ), then ADSB come up into the talks...

https://www.sia.aviation-civile.gouv.fr/media/store/documents/file/l/f/lf_circ_2024_a_001_fr.pdf

In case of GNSS total loss, ADSB-OUT is dead, does TIS-B fill the gap? also, 

• Can one still get own ModeS transponder echo and position from TIS-B using ADSB-IN?

• Given that position comes from ATC radar feeds wouldn’t that be enough for own en-route navigation instead of ATC heading? or reverting to VOR/DME (if any are left)?

There are no plans of TIS-B or ADSB in France yet, maybe in 2030?

Edited January 10, 2024 by Ibra

[kortopates]

You’re thinking of TIS-A where some limited TRACON radar systems give traffic information. Could that be used to see your position? Doubtful, and i don’t recall it giving registration #, just a target W/ altitude.
With TIS-B = ADS/B + ADS/R, everyone that has lost GPS will no longer be able to broadcast ADS/B out position.
If it’s just you having lost GPS, your moving map goes into “coast mode” no longer having own position. Even if you did see other Ads/b targets i assume you wouldn’t know where you were; certainly not to within the RNP 2 requirements even for enroute. I expect you would be forced to change to VOR navigation.

I can’t be certain if the last time i had GPS outage, which was likely from jamming, if i had any ads/b traffic as it was a year ago, but i recall a couple years ago others around us reported loss of GPS too. (this wasn’t in the US).


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[Ibra]

Sorry, yes I was referring to TIS-A but you answered my question, it does not have registration under ModeA/C (without ModeS), so ATC are still in the loop to identify the aircraft, especially, if everyone are using same transponder codes (we have situations where everyone IFR is under 2000 or 1000 squawks if they are using ModeS) 

If TIS-A has systematic aircraft identification (ModeC = known squawk or with ModeS), then it would be enough for own navigation RNAV1 or RNAV2 with onboard equipment while in radar environment (even RNP1 or RNP2 if more radars are used in integrity testing), it would be like using position from ATC radar screen, except one can navigate an airway or direct without ATC assigned headings 

For GPS jamming, yes it would affect TIS-B broadcasts from aircraft and I imagine ADSB-out is dead…is ADSB used for identification or vectoring? that would be an interesting case of contingency (no GPS, no ADSB) by controllers to manage tight airspace 

In France, we only allow idents and vectors using primary return (plus ATC instructions), mode S or assigned ATC code (except in Corsica, where they started one pilot experiment with ADSB due to surrounding terrain near Ajaccio airport)

For GPS degradation, it would interesting to see it GPS failure to achieve required navigation (LOI) does affect ADSB-out signal…I recall losing LNAV on procedure while my iPad kept working, I assume ADSB-out was working as well as it does not care if I was loading a flight plan in GPS? or if I am flying LPV, or TERM, or ENR mode?

 

 

 

Edited January 11, 2024 by Ibra

[jlunseth]

13 hours ago, kortopates said:

You’re thinking of TIS-A where some limited TRACON radar systems give traffic information. Could that be used to see your position? Doubtful, and i don’t recall it giving registration #, just a target W/ altitude.
With TIS-B = ADS/B + ADS/R, everyone that has lost GPS will no longer be able to broadcast ADS/B out position.
If it’s just you having lost GPS, your moving map goes into “coast mode” no longer having own position. Even if you did see other Ads/b targets i assume you wouldn’t know where you were; certainly not to within the RNP 2 requirements even for enroute. I expect you would be forced to change to VOR navigation.

I can’t be certain if the last time i had GPS outage, which was likely from jamming, if i had any ads/b traffic as it was a year ago, but i recall a couple years ago others around us reported loss of GPS too. (this wasn’t in the US).


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I hope they don’t dump all the VORs any time soon. I see GPS outages commonly in specific areas around the Twin Cities, typically near KGYL and KHCD, but other areas as well. More disconcerting, they seem to happen in the middle of approaches. If totally dependent on RNAVs to get down, now what do you do? They typically last only a couple of minutes, so if you hand fly the heading the GPS had you on, it will come back. But I don’t like it at all.

[PT20J]

2 hours ago, jlunseth said:

I hope they don’t dump all the VORs any time soon. I see GPS outages commonly in specific areas around the Twin Cities, typically near KGYL and KHCD, but other areas as well. More disconcerting, they seem to happen in the middle of approaches. If totally dependent on RNAVs to get down, now what do you do? They typically last only a couple of minutes, so if you hand fly the heading the GPS had you on, it will come back. But I don’t like it at all.

Not to worry.

 https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gbng/vormon

[Ibra]

2 hours ago, jlunseth said:

I hope they don’t dump all the VORs any time soon

I had the impression the US will keep it’s core VOR network with good radar coverage as conventional backup for GNSS loss, this seems to be growing rather than shrinking 

In Europe, it’s pretty much toasted for light GA as 1/ the plan by 2030 for most countries is to keep “big DME network” and “some VOR” and 2/ rely on radar which covers mostly big airports at low level and +FL195 

Down here, without VOR, there are no serious backup alternatives for to GPS (other than flying toward VMC or flying high into radar, this means staying above FL195 in many places), there are no DME/DME RNAV avionics for GA? although, if it’s like and death one can calculate arcs himself 

In the other hand, starlink STC are coming to the cockpit, imagine looking online for your registration in FR24 and you navigate using your position? (still need triangulation from Radar or TCAS returns against your ModeS), or better let ATC remotely fly your aircraft while en-route, online 

In the meantime, Trent Palmer got his certificate back 

 

 

 

 

Edited January 11, 2024 by Ibra

[PT20J]

TIS (sometimes referred to as TIS-A although the FAA never used that term) was an add-on to terminal radar mode-S transmissions that provided traffic information at selected terminal locations. With the advent of ADS-B, it became obsolete and has been phased out.

ADS-B traffic comprises a number of services. TIS-B (Traffic Information Service Broadcast) is a broadcast of secondary targets from ground-based radar. Not all airspace requires ADS-B participation and so non-ADS-B out equipped aircraft would not be visible to ADS-B in equipped aircraft without TIS-B. TIS-B ground processing includes a tracker application that removes ADS-B targets from the TIS-B transmission to avoid causing so-called ghost targets to appear near the ADS-B aircraft. 

If there were a prolonged GPS outage and subsequent failure of aircraft to transmit ADS-B out position, I expect TIS-B would still function but I doubt that the ADS-B in equipment in the airplane would be able to process it without GPS position. 

The iPad, as I understand it, uses multiple GNSS receivers, so it may be a useful backup in the event of a GPS outage. 

Skip

[PeteMc]

Following up on what @PT20J said above.  Here are some links to the proposed Decommissioned and Retained VORs.  Both lists are from 2022, but I don't think the FAA has updated either list since then.

https://www.faa.gov/ato/navigation-programs/vor-retention-list

https://www.faa.gov/ato/navigation-programs/vor-target-discontinuance-list

[Ibra]

20 minutes ago, PT20J said:

The iPad, as I understand it, uses multiple GNSS receivers, so it may be a useful backup in the event of a GPS outage. 

iPad mini seems to have multi-constellations, Samsung phone seems to have more as well, iPad Pro seems limited but it does relax tolerances and may use cellular 

Samsung S8 tablet process almost every GNSS & SBAS sats out there (even Glonass, LUCH, BDS…), however, ForeFlight does not run on it, so back to iPad…

 

[Ibra]

Also portable units, like Sentry, seems to have multi-frequency and multi-constellations with their own level of robustness and position tolerances as well different orientation of the antenna (aircraft have two external antenna toward ground and toward sky while portable antenna is shielded from some sides), an example here vs Garmin glass panel going into “dead reckon” while ForeFlight show 9m accuracy, 

ADSB-OUT from GPS -> Transponder did fail, even on RNAV5/ENR leg, 

 

Edited January 11, 2024 by Ibra

[jlunseth]

2 hours ago, PT20J said:

 

The iPad, as I understand it, uses multiple GNSS receivers, so it may be a useful backup in the event of a GPS outage. 

Skip

For whatever reason, the iPad does seem to do a better job of maintaining the GPS connection even when my GTN750 with its dedicated antenna does not.