RAIM Prediction

Doesn’t every IFR GPS have a RAIM checking feature?

I think you have to trigger it manually; I don’t think it does it before every approach. Or does it? I do vaguely recall getting a message once which warned about something.

tomjnx wrote:

I have seen AUGUR generated NOTAMs in the recent past.

However, they do generate NOTAMs only for one specific receiver configuration, while on the web site you can set different parameters which will generate slightly different results.

I used the default parameters in AUGUR. Clearly you can not generally rely on AUGUR to generate NOTAMs.

Peter wrote:

How many sentences there are not bullsh*it?

Even the first sentence is bullsh*it. We have had a “total RNAV environment” for longer than I have been flying in the Eurocontrol system, and I started in 2005.

Basically, GPS has done to navigation what the CD did to vinyl records, and this is a load of job creation for the old guardians on navigational purity.

Just my opinion, you understand…

I don’t think this is bullsh*t at all. It makes perfect sense to me. We do not have a “total RNAV environment”. Just recall the recurring discussions on EuroGA about whether overlay appraches are legal and/or safe. Also, contrary to what is claimed now and then RNAV is not required in all “Eurocontrol airspace”.

Peter wrote:

Doesn’t every IFR GPS have a RAIM checking feature?

I think you have to trigger it manually; I don’t think it does it before every approach. Or does it? I do vaguely recall getting a message once which warned about something.

Yes it does. But the intermediate approach is not the right time to be told that RAIM is unavailable. You should check before the flight. Also, the RAIM prediction feature of GPS boxes only take satellite orbits into account – not outages caused by e.g. planned satellite outages. AUGUR knows about that.

Of course, if you have a SBAS box (and the satellite augmentation is working), you don’t have to bother about RAIM.

We do not have a “total RNAV environment”. Just recall the recurring discussions on EuroGA about whether overlay appraches are legal and/or safe. Also, contrary to what is claimed now and then RNAV is not required in all “Eurocontrol airspace”.

You and I must be flying in different places because I have never done a Eurocontrol IFR flight which wasn’t totally RNAV i.e. virtual waypoints. All of this was RNAV.

I am not sure where overlay approaches (which I guess means using GPS to fly a conventional IAP) come into this. This has never been illegal in Europe, where the regs are written in terms of equipment carriage not equipment usage. It’s up to Jeppesen which stuff to code into their databases.

Peter wrote:

I started reading that CAA document but stopped before sinking into corporate bullsh*it induced depression

Like Airborne Again I find it astonishing that you criticise the CAA for writing that section.

Your objection to the first paragraph is exactly its point: the technologies for a total RNAV environment have been around for two decades. But we don’t have anything like a total RNAV environment because the operational use and deployment of GPS has not been properly coordinated. The PBN concept is trying to coordinate that operational use and deployment.

The second paragraph explains one of the causes: a proliferation of local specifications making it very difficult for operators who ever cross an FIR boundary.

And the third paragraph should be music to our ears. The classic approach to new technology introduction is a mandate: equip or stay on the ground. This is acknowledging that new technology adoption needs to be driven by carrots not sticks.

I hadn’t previously read the introduction to CAP773, but I’m impressed that the CAA author included that section. 10 years ago, the equivalent would just have listed all the reasons GPS can fail.

Peter wrote:

Doesn’t every IFR GPS have a RAIM checking feature?

I think you have to trigger it manually; I don’t think it does it before every approach. Or does it?

There are two RAIM checks. One is done continuously in flight and will display a message (e.g. “INTEG” on a Garmin GNS unit) together with a warning light in your primary field of view when RAIM capability is lost. This can be due to unfavorable satellite constellation (e.g. satellites shaded by mountains when doing an approach into a valley), unusually strong atmospheric attenuation or similar reasons.
The other check is RAIM prediction. It can be performed before flight (e.g. NOTAM, Augur) or any time during flight with suitable onboard equipment. Usually, FMS units with GPS sensors can continuously compute a RAIM prediction for the ETA at destination, but may not warn you if RAIM will not be possible. So in many operations it is standard practice to call up the relevant FMS page and verify RAIM status before commencing the approach. Some FMSs are smart enough to compute a ground speed so that one arrives at destination at a time at which RAIM will be available again.

Peter wrote:

You and I must be flying in different places because I have never done a Eurocontrol IFR flight which wasn’t totally RNAV i.e. virtual waypoints. All of this was RNAV.

There is a difference in using and having to use. It is a fact that RNAV is not required for all Eurocontrol IFR. That doesn’t mean that you can’t use it if you have it.

Earlier (last year, I believe) I posted a (very partial) list of countries and airspaces where you don’t have to use RNAV. But certainly the countries involved were all from eastern and northern Europe where you seldom or never fly.

The generous coverage by sattelites in the moderate European latitudes leads to complacency – even though I probably should, I do not run a RAIM prediction check for the route (is that even possible?) and for destination/alternate I only do it if the landing forecast indicates that I would still be in IMC in FAF.

Just wondering if anybody has ever got into trouble ENROUTE with controllers complaining about actual navigational capability, which could be attributed to reduced navigational performance of GPS? Maybe somewhere in northern Scandinavia? Any pireps please?

Would be nice if the RAIM predictions could be added to the (excellent) autorouter briefings ;)

You don’t need to check RAIM for the enroute phase, only for the approach phase. And you (hopefully ) wouldn’t notice a loss of RAIM or a loss of integrity because the controller complains about your track, but because your GPS unit would tell you.