NEWYEAR quoted this a while back
Yes you can be RNP-10. In the following cases:
6.2 hours after placing IRU in navigation mode (pure inertial), or
5.9 hours after the last automatic DME/DME position update, or
5.7 hours after the last automatic VOR/DME position update.
The FMS continuosly monitors input from the available naviagtion sensors (radios, IRUs, and GNS) to compute a position and actual navigation performance "ANP" value in units of nautical miles. The FMS RNP function is used as a integrrity monitor for airplane position.
If the plane is certificated to fly in RNP-10 airspace then, you can fly without GPS for a flight time not to exceed:
6.2 hrs.
5.9 hrs.
5.7 hrs.
What aircraft is this for, and if not aircraft specific where do you find these details? Never seem them in the 777 FCOM or other documents.
I'm happy enough that on a 777 the loss of both FMC really isn't that big a deal since the CDUs have the current route and any arrival already programmed in their memory, plus ALT NAV lets you program via LAT/LONG. Positional info now just via ADIRU, and slowly degrades over time when out of nav beacon range.
777 just could basically continue (specific airspace dependent), still RVSM, inform ATC (No Mayday probably not even a PAN), and request radar vectors at the far end. Performance from the QRH plus the trusty 3x table.NATS/Oceanic and Polar however are another issue
