Imagine you’re flying in the clouds. You can’t see anything out the window. You’re flying toward the airport on an instrument approach, only a few hundred feet above the ground while traveling at 120 mph, guidance courtesy of a multi-billion dollar miracle we call “GPS”.
You know that GPS is the latest thing. It’s never failed you. Everyone uses it. It’s the future. It’s smart. It’s sophisticated.
And it may be sending you off in the wrong direction.
RAIM is the method an IFR-approved GPS receiver uses to ensure that the data it’s getting from the satellite constellation is valid. I won’t get into the specifics of how RAIM works, but with the world moving ever more toward satellite navigation, this is pretty important stuff.
It always stinks to realize you’ve been remiss in teaching students something they ought to know, and unfortunately, Receiver Autonomous Integrity Monitoring — better known as RAIM — falls into that category.
I’ve got a couple of instrument students right now who are working toward their ratings in glass panel airplanes. One’s in a G1000 equipped DiamondStar and another flies an Avidyne equipped Cirrus SR22. I’ve taught them a lot about Global Positioning System usage, but for whatever reason I have not been insisting that they perform RAIM checks before IFR departures and approaches.
I was reminded of my omission by John at Aviation Mentor. He’s penned an excellent post about RAIM with plenty of nitty gritty details.