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

IRS drift - Details please ?

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

IRS drift - Details please ?

Thread Tools
 
Search this Thread
 
Old 4th Jul 2017, 14:43
  #21 (permalink)  
 
Join Date: Apr 2010
Location: London
Posts: 7,072
Likes: 0
Received 0 Likes on 0 Posts
As Underfire and Asquared point out there are a number of errors or rather inaccuracies that lead to "drift"

You'd imagine that some of them would/should cancel each other out but it never seems to work that way - they always tend to be additative....................
Heathrow Harry is offline  
Old 4th Jul 2017, 14:53
  #22 (permalink)  
Thread Starter
 
Join Date: Oct 2011
Location: Random
Age: 54
Posts: 19
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by FlyingStone
It shows on the FMC yes, together with the FMC altert light. The procedure is in the supplementary procedures in the FCOM.

Thanks for this
Pepperseed is offline  
Old 4th Jul 2017, 15:50
  #23 (permalink)  
 
Join Date: Jan 2011
Location: Seattle
Posts: 715
Likes: 0
Received 3 Likes on 2 Posts
Originally Posted by Heathrow Harry
they always tend to be additative....................
That's because you never know in which direction the errors are. And the number you are after is the worst case, where the errors all conspire together to do you in.
EEngr is offline  
Old 4th Jul 2017, 21:39
  #24 (permalink)  
Guest
 
Join Date: Apr 2009
Location: On the Beach
Posts: 3,336
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Heathrow Harry
As Underfire and Asquared point out there are a number of errors or rather inaccuracies that lead to "drift"

You'd imagine that some of them would/should cancel each other out but it never seems to work that way - they always tend to be additative....................
In the pre-GPS 767 I flew the three IRS positions were essentially triple-mixed in the FMS, similar to the triple-mixing we did with three INSes.

The modern stuff keeps the IRS accurate by continuing tweaking the position with the GPS inputs. If all airframes that are RNP AR qualified had these types of IRU/IRS, the containment assumptions for RNP missed approaches could be significantly less than those used in today's criteria. The RNP missed approach assumes loss of GPS and IRU/IRS drift rates of the older units.
aterpster is offline  
Old 5th Jul 2017, 10:21
  #25 (permalink)  
 
Join Date: Jun 2001
Location: OZ
Posts: 1,125
Received 12 Likes on 6 Posts
Pepperseed, INS DME updating was available provided you had a valid signal from the DME.
EEngr That was the reason for the carouseling, to randomise errors by turning the INU platform at, as I recall it, 4 RPM. It was pretty good with residual errors rarely anywhere even close to the 3+3T limit.
mustafagander is offline  
Old 5th Jul 2017, 12:56
  #26 (permalink)  
Guest
 
Join Date: Apr 2009
Location: On the Beach
Posts: 3,336
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by mustafagander
Pepperseed, INS DME updating was available provided you had a valid signal from the DME.
No so with the INS sets in our L1011/B747 fleet.
aterpster 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



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.