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GPS jamming and spoofing and relying on GPS, and GPS backup plan ?

Airborne_Again wrote:

That surprised me, too. @Timothy, what regulation says you can’t use e.g. a non-SBAS G1000 as primary nav source for enroute IFR? It is approved for LNAV approaches where there is no other nav source, so it seems a bit nonsensical. The AFMS our G1000 C172 simply says that it is “approved” for enroute IFR.

You will find this limitation or similar wording in any TSO C129 AFMS:

When an alternate airport is required by the applicable operating rules, it must be served by an approach based on other than GPS or Loran-C navigation, the aircraft must have the operational equipment capable of using that navigation aid, and the required navigation aid must be operational.

A similar limitation does not exist for most TSO C146 GPS systems.

In the US, to be IFR approved, the installation must comply with AC 20-138 which contains this statement:

TSO-C129 and TSO-C196 are positioning and navigation systems with equipment limitations for the aircraft to have other navigation equipment available appropriate to the operation and for alternate airport flight planning

There is nothing new here. Just means that it is not acceptable to conduct a flight without a functional VOR and any other navigation equipment (DME or ADF) on board as needed to comply with 91.205.

Last Edited by NCYankee at 24 Mar 17:36
KUZA, United States

chflyer wrote:

The note highlighted by Peter was with regards to primary, not sole source. I thought non-WAAS GPS was approved in the US for primary nav as long a another means remained available, as you indicate. Is that wrong?

No. The terms are not well defined, particularly “sole source”. Sole source is not used in the AFMS, there is just a limitation found in the document or the lack of one. TSO C129 has the limitation and TSO C146 with a few early exceptions, does not. Certainly a TSO C129 GPS is approved for enroute, terminal, and NPA GPS approach, it is just that other equipment must be carried in order to satisfy 91.205(d)2.

Two-way radio communication and navigation equipment suitable for the route to be flown.

KUZA, United States

NCYankee wrote:

TSO C129 has the limitation and TSO C146 with a few early exceptions, does not.

Do you have any insight as to why a TSO C146 navigator is acceptable as sole means? It seems as vulnerable to GPS signal-in-space issues as a TSO C129 navigator.

I’d like to transpose into EASA regulation the FAA fuel planning rule that allows a C146-equipped aircraft to plan both destination and alternate airports with only GNSS approaches. I asked the FAA for the safety case, and was technically unconvinced by the answer (even though I was grateful for the helpfulness and responsiveness of those who assisted me).

I presume it is the addition of Fault Detection and Elimination….apparently it can take the USAF up to six hours to shut down the nav signal on a rogue satellite…. a 146 unit will ignore it, a129 unit not.

YPJT, United Arab Emirates

AnthonyQ wrote:

I presume it is the addition of Fault Detection and Elimination

FDE is included in the non WAAS versions of the GNS430/530. That allows use for Oceanic navigation.

KUZA, United States

NCYankee wrote:

FDE is included in the non WAAS versions of the GNS430/530. That allows use for Oceanic navigation.

So the question is, to what extent does FDE mitigate the risk of a GPS continuity failure? If the “rogue satellite” scenario is the main risk, I can see that FDE might justify the all-eggs-in-the-GPS-basket approach to alternate planning. But aren’t there many other GPS continuity failure modes that FDE doesn’t help with?

I also wonder how much GLONASS back up helps? I have a GLONASS feed for my iPad, as a sort of last resort.

EGKB Biggin Hill

Probably depends on how many more Russian “diplomats” get sent back

Administrator
Shoreham EGKA, United Kingdom

Most modern chipsets don’t calculate separate GPS and GLONASS (and GALILEO) positions – they use a mix of satellites as if they belonged to a single constellation. So, GLONASS may be quite useful, especially when you have few satellites in view (though it’s more typical for ground applications than for airborne ones).

LKBU (near Prague), Czech Republic

Ultranomad wrote:

Most modern chipsets don’t calculate separate GPS and GLONASS (and GALILEO) positions – they use a mix of satellites as if they belonged to a single constellation. So, GLONASS may be quite useful, especially when you have few satellites in view (though it’s more typical for ground applications than for airborne ones).

And what would happen if Navstar were simply switched off by the US Military in the face of an offensive launch?

EGKB Biggin Hill
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