Actual navigation performance&required navigation performanc

[Zerafat]

Hi everybody.
Any of you knows what's the reason of this message on CDU?
" Unable TO READ REQUIRED NAV PERF-RNP"

[airknot]

Hi,

If you mean UNABLE REQD NAV PERF-RNP Message

The UNABLE REQD NAV PERF - RNP message shows when the Actual Navigation Performance (ANP) exceeds the Required Navigation Performance (RNP) for the current flight environment. The map data is not blanked in this condition. The flight crew must select a reliable navigation source from the FMC. Check POS SHIFT page for corrupted data. Update with the best NAV sensor data values GPS, DME, or VOR via the MCDU. The FMC position may be overridden by selection of the particular navigation sensor position with the line select key. The selected sensor will now be highlighted and the EXEC light will come on. When you select EXEC, the FMC navigation position changes to the selected sensor position and UPDATE COMPLETE will show at line 5L in small font.

RNP Possible Causes:
Before replacing any component perform BITE of corrupted data source, if known.
1.Flight Management Computer (FMC)
2.Toggling the FMC selector to BOTH on 1 then BOTH on 2, back to NORMAL


useful resource for ref: http://mobile.airlinetechs.com/