RAIM failure?
 

1/ Was wondering if anyone has ever gone to compute RAIM and had it fail? From what I understand in the days gone by with limited GPS coverage it was possible but now highly unlikely.


2/ Has anyone had RAIM issues whilst conducting an approach?

yes, and No.

yes.....




when and where?

Nosey,

That ought to be the least of your failure worries :E

No and no is my answer. :ok:

Just planning for the next one..... and did a bit of research and looks like a very small possibility and if it does occur a very small window of time.

yes, about half way between Bindook, and Camden in NSW, at night, about 6 months ago..

Yes and yes, luckily it was VMC so of no consequence.

Have had GPS lose reception entirely, but low level along the coast, so perhaps some terrain shielding, North of Batemans Bay. Only for 5 minutes or so.

Yes, did a raim prediction before using on a GPS arrival. Computed that raim wasn't available. Ended up being vmc below LSA anyway so the steps weren't required, however the GPS continued to perform normally the entire time.

Doubt you can fly low enough to have terrain shielding when it comes to GPS. Never heard of that reducing GPS navigation accuracy. Have a look at the Queenstown approach charts. You would have to be flying in a tunnel for that to be an issue.

Yes, plenty of times..

Napier, Palmerston North, Queenstown, New Plymouth, Invercargill.

Just to name a few from this side of the ditch.

Yes and yes, but it has been sometime since I have experienced either!:ok:

Yes on approach to YWOL a few years ago (in VMC)

If you plan on using a GPS approach, you are required to do a RAIM check as part of filing the flight plan. There are prediction sites for the airport as well as enroute.
It is especially important at certain locations along the equator and in mountainous area, especially in China and others.

RAIM prediction for enroute will predict how many sats will be available. In reality you need a minimum of 6 sats for navigation. So the prediction will let you know how many are estimated for the final approach and enroute.
Depending on your level required during flight, you may have RAIM failures and have to go to a higher level, or disco the procedure.

Have seen many flights NA into areas of China due to RAIM check on dispatch.