RNP integrity loss in remote airspace
You are in IMC at FL 190 on an RNP 2 route in remote controlled airspace. The GNSS receiver annunciates 'INTEGRITY' and shows ANP 2.4 NM; the route requires RNP 2. You are 80 NM from the nearest VOR/DME, which is 60 NM off track, and 45 NM from an NDB. Radar coverage is not available. The aircraft has one GNSS, one VOR/ILS, one ADF, and no inertial system. ATC has not reported GNSS interference. The minimum enroute altitude is FL 180. The next waypoint is 50 NM ahead and destination is 120 NM ahead. There is no alternate with an approach within 100 NM. Fuel is normal.
1. Interpret ANP 2.4 against RNP 2 and state immediate actions.
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ANP is the estimated 95% position accuracy, and RNP 2 requires ANP ≤ 2 NM for the route. At 2.4 NM the aircraft cannot maintain RNP 2, so the GNSS navigation is degraded. Treat it as a loss of required navigation performance: advise ATC immediately with 'unable RNP 2 due GNSS integrity', and request an alternative clearance. Do not continue on the RNP route as if the alert were a nuisance, and do not use the GNSS for an RNP approach.
2. How can you navigate with the remaining equipment, and what are the limits?
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Use VOR/DME for a position fix and track, with ADF as a cross-check. The VOR is 60 NM off track, so it gives a bearing/distance fix but not a precise route centreline; the NDB is closer but less accurate. Dead reckoning can fill the gap, but at FL 190 wind uncertainty grows quickly. Maintain the MEA of FL 180 and request a route that stays within conventional navaid coverage. If ATC cannot provide vectors or a conventional route, declare degraded navigation capability and divert to a suitable aerodrome; do not descend below MEA to 'get under' coverage.
3. ATC clears you to maintain RNP 2 and says 'expect radar vectors later', but radar is not available. What do you do?
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That clearance does not restore the aircraft's capability. You must be able to comply with the clearance, and with ANP greater than RNP you cannot. Reiterate 'unable RNP 2', request a revised clearance or vectors, and if none is available, declare an emergency if necessary. The priority is separation and terrain clearance, not protecting the route. A promise of radar vectors later does not fix the integrity alert now.