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

B777 - GPS altitude

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

B777 - GPS altitude

Old 25th Dec 2015, 11:48
  #1 (permalink)  
Thread Starter
 
Join Date: May 2009
Location: Switzerland
Posts: 4
B777 - GPS altitude

I am currently doing converstion on the T7 (I am an Airbus kid). Now, during a recent session in the FFS for the Airspeed Unreliable procedure, I was looking for the GPS altitude... until my instructor told me that I will fail to find such.

Now the question: I understand it is not available in the FMC... however, in an other French built airliner, I was able to get it on the FMGC AND via the ACMS and the correct label (GPSALT AFAIK).

Question A: Is there something similar in the T7 or is it simply not possible?

While thinking about it, I thought maybe I could use the cabin altitude indication as a fallback when below 10'000ft (manually open up both outflow valves and maybe turn off both packs to get an approximate pressure indication). This would give me at least an emergency altitude indication if really needed.

Last edited by wolkenjaeger; 25th Dec 2015 at 11:48. Reason: Typo
wolkenjaeger is offline  
Old 25th Dec 2015, 16:01
  #2 (permalink)  
 
Join Date: Dec 2012
Location: FW
Age: 31
Posts: 459
Man...just stick to the qrh...ask atc for the alt...

Fly the ac
Call atc-do qrh

That's it

Happy xmas
fulminn is offline  
Old 25th Dec 2015, 19:20
  #3 (permalink)  
 
Join Date: Oct 2005
Location: FL350
Age: 37
Posts: 22
No mate there is no such thing as GPS Altitude on the 777.You actually confused me for a moment
RAM777 is offline  
Old 25th Dec 2015, 20:33
  #4 (permalink)  
 
Join Date: Jan 2012
Location: USA
Posts: 39
Asking ATC for an altitude is a really bad idea.
CallmeJB is offline  
Old 25th Dec 2015, 22:45
  #5 (permalink)  
 
Join Date: Jun 2001
Location: Boldly going where no split infinitive has gone before..
Posts: 4,357
I attended a briefing by the Boeing 777 tech pilot and this came up.He said GPS alt will be available on the FMC as part of an upcoming update.

And yes, asking ATC for altitude is NOT a gear idea......
Wizofoz is offline  
Old 26th Dec 2015, 08:40
  #6 (permalink)  
 
Join Date: Jun 1999
Location: Oztrailia
Posts: 2,861
Fulmin:----- so mate, how will ATC know you Altitude when your transponder mode C will probably be giving them duff info....

You do know the transponder gets its Alt info from the same place your Altimeter does don't you?
ACMS is offline  
Old 26th Dec 2015, 08:47
  #7 (permalink)  
 
Join Date: Aug 2007
Location: N/A
Posts: 168
777 no GPS ALT. 787 has GPS ALT.....so its not just an Airbus thing.
8che is offline  
Old 26th Dec 2015, 09:41
  #8 (permalink)  
 
Join Date: Nov 2009
Location: flying by night
Posts: 500
787 displays GPS alt on the on the PFD altimeter tapes if pressure altitude is lost - maybe the 777 software update will do just that?

(just like the 787 will also display airspeed computed from AOA on the PFD if pitot static is lost, and standby attitude and heading is also displayed on PFD when needed).

The 787 setup makes perfect sense to me. It's futile to think "what if in the past we had X", but this could probably have saved some lives.
deptrai is offline  
Old 27th Dec 2015, 10:29
  #9 (permalink)  
Thread Starter
 
Join Date: May 2009
Location: Switzerland
Posts: 4
The only answer which really matters:

I attended a briefing by the Boeing 777 tech pilot and this came up. He said GPS alt will be available on the FMC as part of an upcoming update.

And yes, asking ATC for altitude is NOT a gear idea......
Thank you Wizofoz
wolkenjaeger is offline  
Old 27th Dec 2015, 10:42
  #10 (permalink)  
 
Join Date: Oct 2000
Location: Berkshire, UK
Age: 76
Posts: 8,275
Why would it be wrong to ask ATC for the altitude, given that they are using it for separation purposes?
HEATHROW DIRECTOR is offline  
Old 27th Dec 2015, 10:46
  #11 (permalink)  
 
Join Date: Aug 2012
Location: FL390
Posts: 150
Because any Mode-C returns will be potentially invalid due to the pitot/static issues that lead to unreliable airspeed. The altimeter on the aircraft will be displaying the same, potentially incorrect altitude, as the transponder is supplying to ATC. Only a height finding radar that works independently of the Mode C returns would be reliable and these are normally only available to military.
737aviator is offline  
Old 27th Dec 2015, 11:59
  #12 (permalink)  
 
Join Date: Jun 2001
Location: Boldly going where no split infinitive has gone before..
Posts: 4,357
Why would it be wrong to ask ATC for the altitude, given that they are using it for separation purposes?
It was a factor in the crash of the Aeroperu B757 which had blocked static ports.

As a result, the mode C info was corrupted, and ATC were telling them they were at 9000ft when they hit the water.
Wizofoz is offline  
Old 27th Dec 2015, 12:39
  #13 (permalink)  
 
Join Date: Oct 2000
Location: Berkshire, UK
Age: 76
Posts: 8,275
Many thanks for that - understood.
HEATHROW DIRECTOR is offline  
Old 30th Dec 2015, 22:32
  #14 (permalink)  
 
Join Date: Aug 2013
Location: PA
Age: 56
Posts: 34
The 787 is known for transponding incorrect data as well....
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 - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.