Hi guys
just a quick question about the REQUIRED NAV PERF NOT AVAILABLE message on the CDU during an RNAV- LNAV approach.
what is the sequencing/scale down of the rnp during the approach rnp-wise that should the anp exceed it will trigger the message preventing the approach from being continued? In my previous ariplane - the crj - it was rnp1 25nm from the airport reference point, 0.3 2nm prior to faf, 1 from map to missed approach fix and then back to the route rnp.

many thanks

Every leg has its RNP coded in the database, so the entire SID/STAR should be coded with RNP1, the final approach with RNP 0.3 and the missed approach with RNP1. All this is for a standard sequence, a certain procedure might have different RNP required and that should normally be coded in the database.

With FMC U13 you can actually see the coded RNP by pressing DATA on EFIS control panel and it wilk show you the coded RNP for each leg.

Hi
many thanks for the prompt replies.
it is the b737ng FMC. And i thought that the rnp would obey to a more standardized scale down process while approaching the faf and the map, erroneously.

kind regards