GNSS Approach with RAIM Prediction and an RNP Requirement

RAIM (Receiver Autonomous Integrity Monitoring) is an aircraft-based function that uses redundant pseudorange measurements to detect (and with more satellites, exclude) a satellite with an unacceptable error, so that the navigation solution can be trusted to the required integrity for the phase of flight.

• RAIM needs enough satellites in view with suitable geometry; with the minimum set it can only detect a fault, with more it can exclude one. If geometry is poor, RAIM is unavailable and the integrity guarantee disappears.
• An RNP APCH to RNP 0.3 with "RAIM required" means the procedure is only valid when RAIM is predicted available for the whole approach, including the missed approach. Without RAIM, the approach does not meet its integrity requirement and must not be flown.
• The NOTAM GPS outage removes satellites from the constellation for a defined window. That directly reduces the satellite set and can make RAIM unavailable during the overlap with your arrival.
• The correct pre-flight action is a RAIM prediction for the destination and the approach time window (and the alternate), using the operator's prediction tool, and to plan around the outage.

So the NOTAM is not a minor administrative item: it can invalidate the only approach you have.

Options:

1. Adjust arrival time to arrive after the outage window, if holding or a small speed reduction keeps fuel comfortable. This preserves the primary approach.
2. Plan the VOR/DME approach at the destination if one exists and the weather permits; the chart does not say so, so this must be verified.
3. Divert to the alternate with the conventional VOR/DME approach, which does not depend on GNSS integrity.
4. Continue and hope RAIM is available - not acceptable; it makes the integrity requirement a matter of chance.

Decision: do not plan to fly the RNP APCH inside the outage window. The disciplined choice is to plan either a delayed arrival that clears the window with fuel margin, or a diversion to the alternate. With fuel for only one approach plus diversion, there is no room for a missed approach at destination followed by a second attempt; the fuel plan must reserve the diversion fuel and not spend it on a second approach.

If a small delay clears the window with, say, 20-30 minutes of fuel still above the diversion reserve, that is the best option because it preserves the intended destination. If the delay would eat into the diversion reserve, divert. The decision should be made before top of descent, not at the final approach fix.

RNP is RNAV with on-board performance monitoring and alerting. RNP 0.3 means:

• Navigation accuracy of 0.3 NM total system error for 95% of the time, but more importantly:
• On-board performance monitoring and alerting: the system must monitor its own navigation performance and alert the crew if the performance degrades beyond the RNP value, or if the integrity function (RAIM/SBAS) is lost. This is the defining feature that separates RNP from plain RNAV.
• Containment: the procedure is designed with a buffer around the 0.3 NM accuracy, so the aircraft must stay within the containment region; the alerting is what guarantees the crew knows if it does not.
• Crew and operator approval: the aircraft must be approved for RNP APCH, the crew trained and current, and the operator authorised. The chart's RNP 0.3 is a procedure requirement, not a suggestion.
• Database integrity: the procedure must come from a current, valid navigation database; manual entry of RNP APCH waypoints is not permitted.
• Baro-VNAV for LNAV/VNAV: the vertical guidance uses barometric inputs and is temperature-limited; the chart's temperature limits must be respected, and cold-temperature altimeter corrections applied where required.

So even with perfect GNSS accuracy, the approach is invalid without the monitoring, alerting, approval, and database elements.