B777 - GPS altitude
Thread Starter
Joined: May 2009
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From: Switzerland
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.
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 December 2015 at 10:48. Reason: Typo
Joined: Jun 2001
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From: Boldly going where no split infinitive has gone before..
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......
And yes, asking ATC for altitude is NOT a gear idea......
Joined: Jun 1999
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From: Oztrailia
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?
You do know the transponder gets its Alt info from the same place your Altimeter does don't you?
Joined: Nov 2009
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From: flying by night
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.
(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.
Thread Starter
Joined: May 2009
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From: Switzerland
The only answer which really matters:
Thank you Wizofoz
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......
And yes, asking ATC for altitude is NOT a gear idea......
Joined: Aug 2012
Posts: 163
Likes: 4
From: FL390
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.
Joined: Jun 2001
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From: Boldly going where no split infinitive has gone before..
Why would it be wrong to ask ATC for the altitude, given that they are using it for separation purposes?
As a result, the mode C info was corrupted, and ATC were telling them they were at 9000ft when they hit the water.
