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

A320 Flex temperature tailwind

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

A320 Flex temperature tailwind

Old 20th Apr 2016, 05:13
  #1 (permalink)  
Thread Starter
 
Join Date: Dec 2008
Location: Birmingham
Age: 39
Posts: 177
Likes: 0
Received 0 Likes on 0 Posts
A320 Flex temperature tailwind

Hello folks,

What influence has a 5 kts tailwind on the performance calculation. Any rule of thumbs like without tailwind 55 and with a tailwind of 5kt then 45. I want to know in case of short notice of the tailwind and we can take a formula to do a quick change.

Thanks!

Sw
Speedwinner is offline  
Old 20th Apr 2016, 06:54
  #2 (permalink)  
 
Join Date: Aug 2008
Location: Europe
Posts: 12
Likes: 0
Received 0 Likes on 0 Posts
There is no rule of thumb. Takeoff performance can be limited by any of several factors: TODA, ASDA, second segment climb performance, obstacle and so on... You really can`t use any rule of thumb to predict how the 5kt tailwind will influence the takeoff performance in any given case.
vodmor is offline  
Old 20th Apr 2016, 07:07
  #3 (permalink)  
 
Join Date: Jan 2012
Location: Holding at DESDI
Posts: 157
Likes: 0
Received 0 Likes on 0 Posts
Use TOGA!?!? LOL!

Why not just write down the corrections on a piece a paper (from your OFP TLR) and keep it handy. If the tower informs you of a tailwind, just make the corrections on the PERF page. Shouldn't take more than 10 seconds...
J.L.Seagull is offline  
Old 20th Apr 2016, 07:16
  #4 (permalink)  
 
Join Date: Aug 2008
Location: Europe
Posts: 12
Likes: 0
Received 0 Likes on 0 Posts
What if your headwind decreased by 5kts? What if wind changed direction by 20-30 degrees? What if wind changes during the takeoff run? You can`t really take into account any wind variation. What is a chance that actual wind during takeoff will be exactly the same as given in ATIS?
vodmor is offline  
Old 20th Apr 2016, 07:58
  #5 (permalink)  
 
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes on 0 Posts
What is a chance that actual wind during takeoff will be exactly the same as given in ATIS?
That's why the performance calculation uses 50% the head wind or 150% of the tailwind in the maths.

Worst case is a calm wind in the maths, then you pick up a tailwind during the take off.
Goldenrivett is offline  
Old 22nd Apr 2016, 12:20
  #6 (permalink)  
 
Join Date: Apr 2003
Location: Europe
Posts: 3,030
Likes: 0
Received 0 Likes on 0 Posts
If conditions vary that much (variable winds on the ATIS, thunderstorms in the area etc), then surely, as an experienced pilot you would have calculated the takeoff with a tailwind!
PENKO is offline  
Old 22nd Apr 2016, 15:18
  #7 (permalink)  
 
Join Date: Oct 2010
Location: 5° above the Equator, 75° left of Greenwich
Posts: 408
Likes: 0
Received 0 Likes on 0 Posts
If you're operating out of an airport with a long runway, sea level, no obstacles and so on, your 5 kt tailwind might not do too much for you. But if you're about to takeoff from a short runway, or a high elevation airport, or terrain is a concern, you either have a set of calculations previously done handy or you advise ATC you're not ready to depart and run a new calculation. It takes 30 secs on the FlySmart thingy.

Don't modify the performance numbers so arbitrarily, especially on a high performance aircraft. Too many factors contribute to a takeoff to "just add/subtract 5 kts for this or that"
Escape Path is offline  
Old 22nd Apr 2016, 16:14
  #8 (permalink)  
 
Join Date: Mar 2007
Location: Here and there
Posts: 2,781
Likes: 0
Received 1 Like on 1 Post
I have just looked at our paper performance charts for Birmingham. At low weights flex stays the same, at medium weights 5kt tail reduces flex by 2 or 3 degrees and towards the upper end it reduces by 6 degrees until it becomes a performance limit. There is no rule though and you should compute performance from a chart or the flysmart app.
tubby linton is offline  
Old 23rd Apr 2016, 13:58
  #9 (permalink)  
 
Join Date: Sep 2011
Location: London
Age: 53
Posts: 3
Likes: 0
Received 0 Likes on 0 Posts
As Penko rightly says apply the KISS principle and, if variable conditions, just use a tailwind in the initial calcs.

If conditions change dramatically then stop and re do the calcs, it doesn't take that long even without the flysmart software.
energysaver 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 © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.