I tune in the ILS anyways if available and identify it – in that case something goes wrong with the LPV the backup plan is just one push of a (VLOC-)Button away.
Then I have the entire glide slope time to think about how I will fly the missed in case as GPS doesn’t seem to be available…
Peter wrote:
Personally I would always fly an ILS even if I had LPV, because while the tracking (with a modern GPS navigator, and roll steering to the autopilot) will be much better – laterally – with LPV, the signal processing is much more robust on an ILS.
You would only do this until you had flown a bunch of LPV approaches. I gave up flying ILS except for practice about a dozen years ago, too much work (manage VLOC or GPS source, tune ILS, identify ILS, switch back to GPS for miss), too many S turns on final due to crosswind or vehicles/aircraft, snow on the ground, Autopilot unusable below, … In my neck of the woods, the GS is out of service more than LPV 200 is unavailable, which is virtually never. Lightning strikes on the localizer or GS antenna getting the system knocked out for a week at a time doesn’t happen with LPV.
One needs to be a bit careful with that because some autopilots will not intercept a GS except
So if you have to make a rapid switch to the ILS, you may well have to hand fly it all the way down, otherwise you may get the [airbus joke] “WTF is it doing now” moment 
Personally I would always fly an ILS even if I had LPV, because while the tracking (with a modern GPS navigator, and roll steering to the autopilot) will be much better – laterally – with LPV, the signal processing is much more robust on an ILS.
I learned to always put the ILS approach in standby. Helped me last time I accidentally put the GPS into some mode where it didn’t capture anything. The fact that something like this has already happened in the relatively short time I am flying IFR shows me how good that advice was :)
Other causes can be a bad GPS antenna on the aircraft, check for water leaks and or over torquing of the antenna causing cracks.
That‘s true, I had it years ago, but the GPS of the iPad is not affected by this.
For non-certified, you can just make your own stub filter for about £5 in materials.
Yes; exactly what I used to fix the KLN94 issue in the link above. I got well ripped off on the shipping costs though; the company doesn’t know / doesn’t want to know how to send a package to a “foreign country” so they use a 3rd party shipping house which charges c. $250 even for a tiny package
If it is comm interference these work very well in my experience. My GTX335 GPS would drop out immediately (in less than a second) when pushing the PTT on certain frequencies, but the issue was completely resolved for $130 USD plus a few minutes work. I was later told by a local installer that he uses them on every certified GPS installation to prevent similar problems.
The VHF interference check is done easily enough by setting the GPS on a page which shows the space vehicles and their signal strengths. Usually it looks something like this
Then set the frequency – 121.15 is a nice one, 1575/13 – and press PTT for say 20 secs and see if the bars drop.
There are related factors e.g. the ELT PI-tank circuit getting excited by VHF TX near 121.50, and generating so much RF that it saturates the GPS input stage.
