Tech Log The very best in practical technical discussion on the web

B737ng rnp

Old 25th Oct 2018, 00:34
  #1 (permalink)  
Thread Starter
 
Join Date: Sep 2005
Location: italy
Posts: 32
B737ng rnp

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
barrichello72 is offline  
Old 25th Oct 2018, 02:11
  #2 (permalink)  
 
Join Date: Aug 2013
Location: PA
Age: 54
Posts: 36
What is your ac and FMS manufacturer? Depending on the criteria, the approach and missed can be very different. A few bit of information needed.

What was RAIM showing?
underfire is offline  
Old 25th Oct 2018, 05:24
  #3 (permalink)  
 
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 821
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.
FlyingStone is offline  
Old 25th Oct 2018, 10:12
  #4 (permalink)  
Thread Starter
 
Join Date: Sep 2005
Location: italy
Posts: 32
Rnp

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
barrichello72 is offline  
Old 25th Oct 2018, 14:39
  #5 (permalink)  
 
Join Date: Aug 2013
Location: PA
Age: 54
Posts: 36
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.
Yes, many, well all if possible, of the tailored procedures go to 0.3 beginning from the IF, final segment, (some to 0.1) and continue with same RNP level (0.3) through the missed. If RAIM cannot support the procedure through all legs, it will alarm. HIL is another variable to look at. If HIL gets outside the limit for the RNP level, it will also alarm.
underfire is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.