Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

RNAV Approach and Platform Altitude

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

RNAV Approach and Platform Altitude

Old 24th Jun 2020, 11:06
  #1 (permalink)  
Thread Starter
 
Join Date: Feb 2005
Location: TANZANIA
Posts: 163
RNAV Approach and Platform Altitude

I have a question on RNAV approach with full guidance that's LNAV and VNAV, why do we have to select platform altitude ( that's a final approach fix altitude ) when we are cleared for non precision RNAV approach ?


Zenj is offline  
Old 24th Jun 2020, 13:32
  #2 (permalink)  
 
Join Date: Mar 2014
Location: Way north
Age: 43
Posts: 307
"Non-precision approaches" only contain LNAV and LP.

LNAV/VNAV is defined as "Approach procedure with vertical guidance" or APV.

So if you were cleared "non precision RNAV approach", you cannot be flying something with vertical guidance.

But generally you'll be cleared "RNP approach", and select the minimum yourself.

Your question.... I don't know
jmmoric is offline  
Old 24th Jun 2020, 16:53
  #3 (permalink)  
 
Join Date: Dec 2005
Location: UK
Age: 42
Posts: 327
Originally Posted by Zenj View Post
I have a question on RNAV approach with full guidance that's LNAV and VNAV, why do we have to select platform altitude ( that's a final approach fix altitude ) when we are cleared for non precision RNAV approach ?
Why WOULD you? If you're cleared for the approach you would set the first altitude below MDA (Or it won't go down in VNAV!)
rudestuff is offline  
Old 24th Jun 2020, 23:51
  #4 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 1,703
Kinda depends on what airplane we’re discussing, doesn’t it?
Check Airman is offline  
Old 25th Jun 2020, 20:06
  #5 (permalink)  
Thread Starter
 
Join Date: Feb 2005
Location: TANZANIA
Posts: 163
Well I see it being done on A320, E190 and B787
When cleared for approach you set altitude to whats shown on the chart as FAF altitude, so IAF and AF altitudes will always be respected due to VNAV.

Why we set this platform altitude or altitude at FAF? This is my question.
Zenj is offline  
Old 25th Jun 2020, 20:19
  #6 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting home
Age: 42
Posts: 2,915
What position and altitude was this cleared for APCH ?
FlightDetent is offline  
Old 25th Jun 2020, 20:20
  #7 (permalink)  
 
Join Date: Feb 2001
Location: The Winchester
Posts: 5,717
I think on at least one of those types what you do depends on the vertical mode you are using prior to the FAF.

According to one set of SOPs If you have fully checked the FMC etc, are descending in VNAV path ( not for example V/S or FLCH) on the arrival and then when cleared for the approach you can immediately set the MDA..

(I see whilst I was typing Alpine Flyer has covered the "trap")
wiggy is offline  
Old 25th Jun 2020, 20:22
  #8 (permalink)  
 
Join Date: Jun 2001
Location: at the edge of the alps
Posts: 361
Once you're on VNAV you could also set the missed approach altitude (which you could also do once established on the final altitude while waiting for GS intercept). One reason not to to that could be maintaining uniform procedures over different approach types and/or better protection in case you decide for whatever reason to change from VNAV to VS or FLCH (e.g. in response to an "increase rate of descent" command) before being established at the FAF altitude.
Alpine Flyer is offline  
Old 26th Jun 2020, 09:03
  #9 (permalink)  
Thread Starter
 
Join Date: Feb 2005
Location: TANZANIA
Posts: 163
Usually you set missed approach altitude when you get a green indication of GP or VGP depending on the type, this is exactly like ILS where you set missed approach after getting G/S captured.

So like ILS approach where you also set platform altitude ( FAF altitude ) before the approach, we also set the same for RNAV approaches with VNAV guidance, why do we do this ?
Zenj is offline  
Old 26th Jun 2020, 09:14
  #10 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting home
Age: 42
Posts: 2,915
Rephrase and ask again, lost in the translation.
FlightDetent is offline  
Old 26th Jun 2020, 12:53
  #11 (permalink)  
 
Join Date: Mar 2012
Location: Having a margarita on the beach
Age: 47
Posts: 1,667
Originally Posted by Zenj View Post
I have a question on RNAV approach with full guidance that's LNAV and VNAV, why do we have to select platform altitude ( that's a final approach fix altitude ) when we are cleared for non precision RNAV approach ?
How You will fly an APV is very much type/company specific.
What type to start with ?
sonicbum is offline  
Old 26th Jun 2020, 18:29
  #12 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 2,556
Originally Posted by Zenj View Post
I have a question on RNAV approach with full guidance that's LNAV and VNAV, why do we have to select platform altitude ( that's a final approach fix altitude ) when we are cleared for non precision RNAV approach ?
I take it that you're higher than FAF and you are cleared for approch. You will have to descend to FAF or platform altitude or FINAL APP will not engage from above. It can intercept the path from below but not from above.
vilas is online now  
Old 27th Jun 2020, 02:28
  #13 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 1,703
Originally Posted by vilas View Post
I take it that you're higher than FAF and you are cleared for approch. You will have to descend to FAF or platform altitude or FINAL APP will not engage from above. It can intercept the path from below but not from above.
I’ve always wondered why it had this limitation. Do you know if FLS is the same?
Check Airman is offline  
Old 27th Jun 2020, 13:06
  #14 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting home
Age: 42
Posts: 2,915
On the A320 when intercepting from above, the FINAL APP will engage. Of course only if the waypoints are correctly sequenced and once you position
sufficiently close to the geometrical profile.

Last edited by FlightDetent; 27th Jun 2020 at 15:20.
FlightDetent is offline  
Old 27th Jun 2020, 14:44
  #15 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 2,556
There's only very small margin from above and in an Airbus presentation it is not recommended. Main thing is FINAL APP mode is designed to fly only between Final Descent Point down to applicable minima. It is not capable of flying any level off segments with altitude constraints before final descent point. That must be done in Des mode.
The To way point must be the FDP is one of the conditions for engagement of APP mode. So if vectored sequencing to FDP(Not beyond) is mandatory.
vilas is online now  
Old 27th Jun 2020, 15:37
  #16 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 2,556

The last condition VIP stands for vertical intercept point same as FDP.
vilas is online now  

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 - Do Not Sell My Personal Information

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