Yes that what I said 
SBAS signal AND TSO146 = NO RAIM
RAIM is always running on most GPS navigators. The criteria changes based on the mode being used. Enroute, Terminal, or Approach. RAIM prediction is determining if RAIM will be able to run at a point in space and time based on the navigation mode.
Ibra wrote:
If SBAS is available and box is TSO146: RAIM does not exit
It does it exist and is used anytime outside an SBAS service volume or a failure of the SBAS system.
Assuming SBAS is not available or flying non-SBAS TSO129, like KLN or GNS430
Sorry will have to introduce new names & objects 
yes there is RAIM PREDICT: prediction of integrity, this can be run manually by PIC on AUGUR, PIC on GPS and automatically by GPS near FAF, then there is an automatic RAIM FDE: actual integrity check using fault detection and exclusion
Indeed, pressing GPS for “RAIM PREDICT” during flight is largely unessessary but it’s more complicated than that:
1) On ENR cruise, if you are within your IAP EAT the RAIM PREDICT check will be exactly the same one you did in AUGUR before takeoff: it will not notice that giant dinosaur did swallow the whole orbit, I also understand RAIM PREDICT is not required for RNAV5 and RAIM FDE will not run on RNAV leg, 4 satellites to get a position and you are good for RNAV5 cruise?
2) On TERM cruise, RAIM FDE will not run BUT the pilot is expected to have RAIM PREDICT to fly RNAV1 legs (STAR, IAP or simply if you are 30nm from FPL destination without even loading an approach), it does not make sense but it’s a planning rule
3) On IAP approach, RAIM PREDICT will run automatically before FAF to show a final leg annunciation then RAIM FDE will run if it’s an RNP leg
I agree on 3) it is unnecessary (done by the box anyway before FAF) but I would carefully to check RAIM for 2), especially if STAR has 50nm or my if EAT changes: I think you will need to check RAIM even of not flying an RNP approach at destination as you expect to fly RNAV1…
Maybe this “tradition of mannual RAIM check during flight” comes from old days where no offline site was available? or when some approaches were designed with RNAV1 for final segment? will GPS run RAIM predict and actual magic before or after FAF on these @NCYankee?
Some examiners or instructors tells you to check RAIM on descent from cruise because 3) which I agree is not necessary but maybe it’s a mis-understanding of one way to comply with 2) or “legacy” reasons?
PS: you definitely need RAIM check during flight before DIY IAP on GPS, unless you code RNP0.3 leg in navigator yourself, everything will be on RNAV1 near destination without FDE
If SBAS is available and box is TSO146: RAIM does not exit
Ibra wrote:
During planning: before staring the aircraft one has to check RAIM for RNAV1 terminal legs (departure SID, arrival STAR) and RNP0.3 legs
Here,
https://augur.eurocontrol.int/tool/During flight: by actually pressing Navigator menu and run the check themselves before starting RNAV1/RNP0.3
What you do before the flight is not checking RAIM but checking RAIM prediction for the duration of the flight (or at least the times when you actually need RAIM). There’s no point of doing that once you’re airborne. The box will tell you at once if RAIM is no longer available.
For Europe RAIM checks, I think they depend on the box, the flight leg and if it’s planning/flight
TSO129 GPS-NW non-SBAS box
During planning: before staring the aircraft one has to check RAIM for RNAV1 terminal legs (departure SID, arrival STAR) and RNP0.3 legs
Here,
https://augur.eurocontrol.int/tool/
During flight: by actually pressing Navigator menu and run the check themselves before starting RNAV1/RNP0.3
TSO146 GPS-NW SBAS box
During planning: no RAIM check is required but one need to read the “GPS NOTAMS” for SBAS availability
During flight: if SBAS is lost, GPS reverts to RAIM checks and vertical guidance is lost
- GPS “only” needs 4 stats to fly RNAV1 for the missed during an LOI
- TSO129 GPS-NW would run RAIM with fault detection on 5 sats
- TSO146 GPS-W would run RAIM with fault detection & exclusion on 6 sats
If GPS sats drop to 4 sats, it show “LOSS OF INTEGITY”, the 3D position is still very correct but GPS has no internal way to check it
If GPS sats drop to 3 sats, it show “NO GPS POSITION” on screen fly “DEAD REC”
NCYankee wrote:
It does not appear to be based on the locations of the ground monitoring stations.
Thanks, so being near RIMS station will not change much the parameters for any of the integrity tests but definitely help to reduce position accuracy errors…in other words, it cannot be used for “practical purposes”
Ibra wrote:
So error in SBAS corrections are mostly interpolation errors over wide area but near the RIMS station the correction should be very accurate…On integrity, would you get more “LPV downgrade” when operating far away from ground stations than say “LPV downgrade” when operating near ground stations? or integrity is unrelated to SBAS correction accuracy?
As best I can determine, SBAS provides 16 coded values (0 to 15) that specify the integrity of each individual satellite and it applies to the entire service volume. A value of 15 is “Do not use” and 14 is “Not Monitored”. Codes 0 thru 13 are used to specify a UDREIi of 0.75 meters to 150 meters. The GPS uses its position and the integrity of each satellite to determine an overall integrity HPL or VPL for the aircraft position. It does not appear to be based on the locations of the ground monitoring stations.
RobertL18C wrote:
Is my assumption (I think it may be stated in an FAA old GPS guide?) that if RAIM is unavailable past the FAF, and there is in effect Loss of Integrity, the GPS operates in ded reckoning mode? and it announces Loss of Integrity once you sequence to the waypoint after the missed approach point?
Robert,
If RAIM is unavailable, it means that integrity can’t be determined. If RAIM was still available at the FAF, you can continue along the FAS, even if RAIM is not available. In this case, the RAIM integrity can’t be determined, but since integrity was still valid at the FAF, the integrity is assumed to not deteriorate for the remaining flight to the MAP.. That is different than the case where RAIM is available and the integrity is less than required for the FAS.
An example, 4 satellites are needed for a position. A fifth satellite is needed to calculate RAIM. The position will be based on the 4 satellites that offer the best geometry. The question is can you trust them to provide a suitable accuracy during the approach. The fifth satellite is substituted for each satellite, one at a time to produce another 4 positions. The differences in the 4 additional positions are used to determine how trustworthy the original 4 satellites are in producing a position. At the FAF, the four satellites producing a position are found to be producing a trustworthy position. Then after the FAF, the fifth satellite is no longer being received, so now there is no way to determine the 4 additional positions to perform the integrity check. As long as the 4 satellites that are used to provide the position remain available, it is highly unlikely that their position accuracy will change of the remaining 2 minutes of the flight to the MAP. That would be RAIM unavailable. On the other hand, if all 5 satellites remained usable, the RAIM algorithm could still be available and if at any point on the FAS, the RAIM calculation indicated that the 4 satellites providing the position were not providing sufficient integrity, then using the GPS to continue the approach is not warranted. The integrity may still be good enough to execute the missed approach. If the integrity is not sufficient for that purpose, then one must revert to alternate means of navigation not using the GPS.
NCYankee wrote:
RAIM being unavailable means the inputs to the algorithm are insufficient for the RAIM algorithm to check integrity. That is a different state from the RAIM algorithm determining an integrity fault. That is why if RAIM is still available at the FAF, the approach can continue, even if it is lost on the FAS.
@NCYankee many thanks and appreciate the other posts. Is my assumption (I think it may be stated in an FAA old GPS guide?) that if RAIM is unavailable past the FAF, and there is in effect Loss of Integrity, the GPS operates in ded reckoning mode? and it announces Loss of Integrity once you sequence to the waypoint after the missed approach point?
Ibra wrote:
So the only technical difference between GBAS and SBAS is “ionospheric delay”, which has a historical average of “5m error” on RIMS stations (there is also satellites position error as they move up/down from their flight path but that should be corrected same way between SBAS as GBAS)
Of course both GBAS and SBAS correct for ionospheric delay. The difference is that GBAS gives correction for a particular spot based on measurements on that spot so it doesn’t have to distinguish between different kinds of errors. Also the correction will be as good as it gets. SBAS gives corrections within a very large area based on measurements at various places in that area so the correction has to be estimated for most locations. When making that estimate various error sources (e.g. ionospheric delay) have to be considered separately.
