Originally Posted by
Da40Pilot
Ok, I think I may have found the answer thanks to the answer options you provided...I pulled up the old trusty Jepp Instrument/Commercial textbook and here's what it says:
"Some receivers have the additional ability to isolate the corrupt satellite and continue reliable operation with the remaining satellites. This requires an additional satellite beyond what is required to identify a RAIM error, a total of six."
You have error isolation and error detection. To have a good RAIM signal, you only need 5 satellites. If you want the receiver to remove an invalid or corrupted signal from the solution you need to have a 6th satellite to replace the corrupt one.
3 satellites will give you a 2D fix in space (triangulation)
4 satellites will give you a 3D fix in space
5 satellites is the minimum required for RAIM. If one satellite starts giving a signal error or integrity is in question, the receiver can only say that one signal is bad and will not enter APP mode or will remove all GPS navigational information from an HSI
6 satellites can replace a bad signal allowing you to continue an approach without losing signal integrity.