Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Flight Info Question  
User currently offlinewardialer From United States of America, joined Sep 2001, 1183 posts, RR: 0
Posted (3 years 7 months 1 week 4 days 23 hours ago) and read 2264 times:

Hi Guys!

I just wish to know on how does this Flight Information (from the below image link) know the Time to Destination if the Ground Speed is 0 mph?
Doesnt the flight computer start calculating the Time to Destination when the Ground Speed is active?

Please shed some light on this....Thx.

http://www.airliners.net/uf/view.fil...?id=126150&filename=phpEeiWR7.jpeg

3 replies: All unread, jump to last
 
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 1, posted (3 years 7 months 1 week 4 days 23 hours ago) and read 2253 times:

Quoting wardialer (Thread starter):
I just wish to know on how does this Flight Information (from the below image link) know the Time to Destination if the Ground Speed is 0 mph?
Doesnt the flight computer start calculating the Time to Destination when the Ground Speed is active?

When was this photo taken? If it was taken on the ground, the FMC is just spitting out the expected flight time based on the input flight plan.

Tom.


User currently offlinewardialer From United States of America, joined Sep 2001, 1183 posts, RR: 0
Reply 2, posted (3 years 7 months 1 week 4 days 22 hours ago) and read 2243 times:

Its not my picture, but I believe its on the ground at the parking gate.

But how does the FMC know the predicted Ground Speed?

And since the Ground Speeds are not fixed through the whole entire flight due to winds aloft, and the flow of the jetstream, I still do not understand on how it will predict the exact Ground Speed in order to calculate the Time to Destination.

[Edited 2011-02-12 12:00:01]

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 3, posted (3 years 7 months 1 week 4 days 22 hours ago) and read 2233 times:

Quoting wardialer (Reply 2):
But how does the FMC know the predicted Ground Speed?

It doesn't. That screen is showing actual ground speed (provided by the avionics) and *planned* time to destination (calculated by the FMC). Once you're airborne, it will show remaining time to destination.

Quoting wardialer (Reply 2):
And since the Ground Speeds are not fixed through the whole entire flight due to winds aloft, and the flow of the jetstream, I still do not understand on how it will predict the exact Ground Speed in order to calculate the Time to Destination.

The FMC gets a flight plan, a cruise speed, and winds aloft (and cost index and a bunch of other stuff). It calculates time to destination from current position based on that information...that's what's showing on the screen. The FMC is not predicting ground speed, that's an input based on the current instantaneous state. The FMC will update time to destination as the flight progresses but, on the ground, it's not paying attention to current speed.

Tom.


Top Of Page
Forum Index

Reply To This Topic Flight Info Question
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
EWR-HKG Flight Path Question posted Thu Jan 3 2008 08:16:06 by Nbseer
Flight Crew Question posted Tue Aug 21 2007 00:40:51 by THEENGINEER
747-400 Flight Deck Question posted Wed Dec 27 2006 16:07:42 by Gkyip
Specific JP8 Fuel Info Question posted Wed Dec 20 2006 18:20:55 by RIHNOSAUR
Flight Routing Question (from UK) posted Thu Sep 29 2005 18:08:45 by Gkirk
Thomas Cook UK - Requesting Flight Info posted Fri Jun 24 2005 16:54:26 by RichM
Flight Test Question posted Fri Jan 21 2005 19:12:34 by 2H4
C8 Flight Level Question posted Sun Nov 14 2004 10:09:24 by Tiger119
United Flight 895 Question posted Tue Oct 12 2004 01:23:29 by Bruce
Flight Identification Question posted Wed Apr 21 2004 05:13:16 by Goboeing

Sponsor Message:
Printer friendly format