B777 - GPS altitude

[wolkenjaeger]

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. :eek:

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.

[fulminn]

Man...just stick to the qrh...ask atc for the alt...

Fly the ac
Call atc-do qrh

That's it

Happy xmas

[RAM777]

No mate there is no such thing as GPS Altitude on the 777.You actually confused me for a moment :)

[CallmeJB]

Asking ATC for an altitude is a really bad idea.

[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......

[ACMS]

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? :D

[8che]

777 no GPS ALT. 787 has GPS ALT.....so its not just an Airbus thing.

[deptrai]

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.

[wolkenjaeger]

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

[HEATHROW DIRECTOR]

Why would it be wrong to ask ATC for the altitude, given that they are using it for separation purposes?

[737aviator]

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.

[Wizofoz]

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.

[HEATHROW DIRECTOR]

Many thanks for that - understood.

[underfire]

The 787 is known for transponding incorrect data as well....