FPV on the B 777

[pilotin777]

Why is it that Boeing recently modified the rules on when and why to use FPV ?
The Airspeed Unreliable C/L actually says Do NOT use Flight Path Vector.....
Previously, it was mentioned as a source of good, useful information.....
Your thoughts????

[gums]

Duhhhh?

Can't get a good source describing that FPV for the T7, but isn't it inertial or maybe GPS-aided inertial?

Having had a pitot-static freeze up one day, that sucker was priceless. We lite pukes have had great flight path markers since 1968 or so in the A-7D, F-14, F-15, F-20 prototype, F-22 and F-35.

I think about AF447, and how much a good FPV might have helped.

[Ghost_Rider737]

If AF 447 was a Boeing , all would be well today !

This crap about static thrust levers and non sensory feedback side sticks is the problem !!!

The Capt has no idea what the FO is doing and vice versa !

Boeing has a decent (as close to conventional) FBW design , Airbus have made it Fly By Wireless !!!

[Denti]

Can't comment on the 777, on the 737 the FPV is inertial but uses barometric altitude inputs from the ADIRUs. Boeing warns that it is unreliable with unreliable primary altimetry information. However, there is no information about speed information. There is no information about the FPV in the airspeed unreliable checklist, however there is a big note which could explain while it is not entirely wise to trust it completely.

Note: Erroneous or unreliable airspeed indications may be caused by blocked or frozen pitot-static system(s), or a severely damaged or missing radome.

Since the FPV takes static system inputs any malfunction that includes the static system may lead to wrong indications.

[bungeeng]

Why does the FPV need air data?

[NSEU]

You may find the answer somewhere in this convoluted thread...

http://www.pprune.org/tech-log/452973-fpv-fpv-cage.html

[misd-agin]

Denti - was told 777 has similar issues(air data input?) so the FPV might be wrong when you need it most.

[Sciolistes]

Denti,
There is no information about the FPV in the airspeed unreliable checklist, however there is a big note which could explain while it is not entirely wise to trust it completely.
Since the FPV takes static system inputs any malfunction that includes the static system may lead to wrong indications.
But the 737 FCTM goes to great length to say how groovy the FPV is with unreliable airspeed :confused:

[CharterJake]

I can't comment on the Airbus 'bird' and I don't remember much from the 737 NG, but the 777 FPV uses both inertial data and air data inputs from the ADIRU/ADM. Therefore if you have an unreliable airspeed situation Mr. Boeing says not to use it because the displayed information by the FPV MAY be compromised. May and not will, but if you follow incorrect data and it is not picked up by either of you by crosschecking pitch/power through different flight phases (and possibly in very high workload situations), then it's no good is it? Pitch-power, nail it and hold it with minor and smooth adjustments.
Somebody asked why does it need air data? I'd love to know as well, if anybody has any idea about it, please share it.

[Ka8 Flyer]

The FPV needs air data to compensate over time.
Inertial data will only provide accurate accelerations. Velocities will always drift with time and to accurately indicate the vertical component of the FPV, you'll need to correct for those errors and that's where air data comes into play.
Just like the IVSI uses inertial data for the initial and fast pointer deflection, the long term averaged vertical speed comes from air data.

The sim replicates this nicely when the statics are blocked: you'll see the VSI fluctuate if you climb / descend but it settles back down (due to the blocked ports).