Doesn’t the RNAV system constantly use GPS and DME/DME (and maybe VOR/DME) as input for an integrated positioning including comparing/filtering the results? If the GPS gives “impossible” results, like position suddenly moving and crazy ground speeds, isn’t its data automatically filtered away, and the RNAV box looses precision but continue with DME/DME (and maybe VOR) data?
It seems that algorithms in existing equipment have not been developed that way. GPS has priority and spoofing confuses the software to the level that GPS has to be disabled and position has to be established using conventional nav aids. Jamming is easier to fight against.
JohanP wrote:
Thinking about it, if you can jam a GPS signal, you can also jam a VOR signal, so I don’t see why VORs are safer.
The GPS signal received is extremely low power levels (-160 dBW = -130 dBm). It’s really quite a miracle that small electronic devices can capture and lock on to it, which is why it only needs a very small amount of RF jamming (at the receiver) to disrupt it. High power jammers can cover quite a large area.
By contrast, VOR transmitters put out a much higher power signal and are shorter range than satellites, so would require a comparatively much larger jamming signal to disrupt.
In my view, the main point is to have a backup plan if you lose your position, both VFR and IFR. For PPL skill tests we check the student can position fix and then track a using a ground radio navigation aid. In the FRTOL radio test, the student has to demonstrate knowledge of requesting a position fix from ATC/FISO.
Apologies for only naming SkyDemon as the moving map app. Of course others are available, and the CAA do seem careful to use the generic term “Moving Map Display” which I understand also includes onscreen mapping (eg. G1000).
DavidC wrote:
In my view, the main point is to have a backup plan if you lose your position, both VFR and IFR.I can only comment on the VFR of course, but this is interesting – I continuously cross check what I see on the moving map with what I see on the ground, so a) I hopefully notice getting spoofed and b) I am not requiring a fix when getting jammed because the last position is reasonably well known and I could go from there.
Another thing by the way – the less time and mental capacity you spend on navigating, the more time you have for aviating, which includes looking out for traffic.
I did my PPL lessons and test in summer 2011 and I’m quite satisfied with how I was taught and tested. The nav was all dead reckoning plus a bit of VOR/DME/ADF, plus making sure we knew how to do simple stuff (a direct-to and a flight plan) in the GNS430. SkyDemon came afterwards and of course it’s now my primary means of navigation but I tend to think if you really can’t teach yourself moving map GPS, having already been taught to navigate the hard way, then you might think about whether you have the smarts the fly an aeroplane.
I’ve only once had a failure of GPS nav, shortly after leaving White Waltham on my way back to Enstone, a route that I often fly. I won’t bore you with exactly what the failure mode was and why it couldn’t be reset in flight, but I was in a RV8 with no other navigation equipment and it was a choice of go back into Waltham to reset things or continue to Enstone. I had a old chart with no line drawn on it and certainly no plog. I had no ruler or protractor so had to guesstimate the desired track and wind correction, distance, time, etc.
I continued and everything was fine, but it certainly wasn’t a picnic. Given I’d not used any dead reckoning at all for serveral years I was pretty rusty – it’s not that it’s actually difficult to do but it’s just a more stressful environment – having to wait for confirmation of your position to appear rather than being able to check it at any time. More than anything I was determined not to have to call Oxford Radar and ask them for a steer, and things happen faster at 150kts than they do in the training PA28 at 95kts.
So that was my experience, on a simple and short route that I knew well and with the knowledge that I could always get a steer from ATC if it went wrong. A pilot who’d done plenty of DR and got it down to a fine art some 11-12 years previously.
So if the route isn’t this short and trivial and the pilot has only done a tiny bit of DR to establish the principle – an unplanned diversion or simulated GPS failure – will they be able to do it? I think probably not.
If you drop DR from the test standards then you probably need to mandate GPS fitment and then loss of GPS becomes a semi-emergency. Not sure we want to go there?
Besides, what are they going to fill 45hrs with if they drop DR?
DavidC wrote:
I presume this is a first and that no other European country permits the use of SkyDemon etc in skill tests. Is that true?No, I used Skydemon during my PPL skill test in Germany back in 2018. Actually, I had already a TMG license on LAPL, but it was my SEP on PPL skill test. The examiner liked my approach to use an EFB app and he let me explain the entire preparation. He said that “EFB apps are the future” and “paper is old school and not environmental friendly”. My proposal was actually seen as a plus, instead of a disadvantage.
I think the debate is whether to allow GPS for the PPL skills test officially, and this then leads to the obvious Q of whether the examiner is allowed to insist on it (if installed in the panel; this has been the case in the US for many years and very sensibly).
It is very controversial, not least because the PPL schools do not want to be pushed into any extra costs. Some 90% of customers pack up without really using the PPL so why do it? Also a small subset of PPL students are so non-technical that they struggle with any “gadget”, yet they still have the ~15k to donate to the school 
There is no doubt GPS should be introduced in post-PPL tests, because it is practically impossible to fly without it 
The use of onboard GPS navigation (Garmin) was tested during my both skill tests.
