Originally Posted by
Check Airman
The preflight RAIM check is just a prediction. It's possible that they did a "live" check at the start of the approach, and found that RAIM was available. The avionics will also let you know real time if RAIM is unavailable.
Not saying it was right- just raising a few possibilities.
What was the wx at the time? If it was VMC, they may have been able to fly the procedure without RAIM.
As far as I know there is no way to check RAIM availability on B737. The WX was IMC.
Originally Posted by latetonite
A RAIM prediction is just a prediction. What you fly on is ANP. If you could get a better ANP than the RNP, you are good for the approach.
OK, I was thinking about that too, but consider this: If RAIM is not available then the computer is not able to detect a bad signal from satellite. So if a bad signal cannot be detected the ANP will not reflect the actual performance at all. RNP approaches are ONLY allowed based on GNSS sensors, so it seems to me that without RAIM, the ANP reading is useless. Isn't that right?
Originally Posted by custardpsc
pilotnik - what the others said - if the augmentation is satisfactory ( EGNOS in eu, WAAS in USA) then no need to check RAIM.
But I didn't get Empty Cruises point about LPV minima. I know that LPV requires WAAS but if you have integrity and there are no LPV minima what stops one using LNAV/VNAV approach / minima ?
I think you guys have a wrong idea on the RNP approaches, BUT it may also be that it is me who is wrong
From what I have read SBAS (or WAAS in USA) is only used for LPV approaches. It has nothing to do with LNAVs or LNAV/VNAVs. The only GNSS augmentation for the purpose of RNP APCH to the LNAV or LNAV/VNAV minimums is RAIM.