Random 777 questions, part 1

[wiggy]

Originally Posted by Turbo Encabulator

Here's one. How come VNAV routinely starts down at TOD and suddenly decides that it's 2000 feet low on path and reverts to VNAV SPD? I"m like you're the one who calculated the TOD point

I know VNAV has it's quirks but FWIW I had few thousand hours on the T7 and can't say I ever saw what you describe happen as a matter of routine.

Given old age I can only guess I'd be suspecting maybe winds (the point Uplinker made)/ or, and I'm clutching at straws here - programmed descent speed vs. programmed cruise speed - does it routinely happen if you transition from Econ cruise to Econ descent?

[tdracer]

Originally Posted by eckhard

I think RR engines adjust fuel flow to keep the EPR constant, whether or not engine TAI is selected, hence no perf correction?

All FADEC engines (in "Normal" mode) adjust the fuel flow to keep the target N1 or EPR - Rolls is no way unique in the that regard. The EAI debit is to protect EGT margins.
However, since anti-ice is normally only used when it's cold - well below the rating corner point for the Takeoff rating range - not everyone bothers to take a performance debit for anti-ice for Takeoff. Max Climb/Max Con are a different issue.
Some models permit dispatch with an EAI valve locked open (which can happen when it's pretty warm), but that's typically handled via the MEL.

[eckhard]

ok, thanks.

[Turbo Encabulator]

Originally Posted by wiggy

I know VNAV has it's quirks but FWIW I had few thousand hours on the T7 and can't say I ever saw what you describe happen as a matter of routine.

Given old age I can only guess I'd be suspecting maybe winds (the point Uplinker made)/ or, and I'm clutching at straws here - programmed descent speed vs. programmed cruise speed - does it routinely happen if you transition from Econ cruise to Econ descent?

That's usually when I see it. Winds were my first thought as well, but I'm not sure that's it. "Routine" might be an exaggeration but it certainly hasn't been a one-off. I'll see it a couple of times on a given trip and then not see it for a couple of trips.

[EY EVP]

B777 stab trim levers

What/when are manual stab trim levers on center pedestal for ? They are not mentioned in any non normal checklist. When to use ?

[ScepticalOptomist]

Originally Posted by EY EVP

What/when are manual stab trim levers on center pedestal for ? They are not mentioned in any non normal checklist. When to use ?

If the dual switches on the yoke failed you would still be able to trim the aircraft.
I imagine not everything is in a checklist and some aspects of the operating the jet require the pilot to, well, be a pilot.

[eckhard]

Don't know if this applies to the 777, but on the 787:

"If there is a complete loss of flight control signalling, direct wiring from the flight deck to the stabilizer and a spoiler pair allow pilot control of pitch using the alternate trim switches and roll using the control wheel."

[DNEMtin]

Weird question, but still…
What is exact size of a small pitch rectangle on PFD (in degrees)?
In other words: What will be the pitch angle, if I just touch the 5 degree line with rectangle, then, if I keep inline the upper edge of the rectangle and the 5 degree pitch line?

[punkalouver]

Originally Posted by EY EVP

What/when are manual stab trim levers on center pedestal for ? They are not mentioned in any non normal checklist. When to use ?

Originally Posted by ScepticalOptomist

If the dual switches on the yoke failed you would still be able to trim the aircraft.

In other words, you can use them for normal ops(but not allowed when the autopilot is engaged). Try it in the sim sometime.

[olster]

Vnav influenced by wind and temperature variation?

[Turbo Encabulator]

Originally Posted by Turbo Encabulator

Here's one. How come VNAV routinely starts down at TOD and suddenly decides that it's 2000 feet low on path and reverts to VNAV SPD? I"m like you're the one who calculated the TOD point

Update: This only routinely happens on the NEEL6 arrival into ANC. There is an above FL250 restriction at HAMND, and T/D is always directly on top of HAMND unless you delete the altitude restriction, in which case the T/D moves a considerable distance varying on CI. Seems like a database issue, now just curious if anyone else has seen this on that arrival or anything similar on others.

[Gweilo747]

Originally Posted by Turbo Encabulator

Update: This only routinely happens on the NEEL6 arrival into ANC. There is an above FL250 restriction at HAMND, and T/D is always directly on top of HAMND unless you delete the altitude restriction, in which case the T/D moves a considerable distance varying on CI. Seems like a database issue, now just curious if anyone else has seen this on that arrival or anything similar on others.

I have seen this…..I agree, but now I’m confused - is the TOD point predicated on CI, descent winds, or both?