B777 One F/D on the other off when visual

[puff m'call]

I'm having a brain fart!!

Why do we switch the PNF's F/D on when flying visual, something to do with the go-around?

[despegue]

Huh?

Either all F/D on or all OFF. To avoid confusion.
On a visual, just put them both OFF.

[skkm]

When a go-around is initiated, the FD will appear on both PFDs, regardless of the switch position. However, as soon as the first mode change occurs (LNAV or VNAV, most likely), the flight directors will disappear again if the switch is off. Thus, I imagine the PM's FD switch is turned on so that in the confusion of an unexpected go-around, someone will still have persistent FD guidance.

[flapsupdown]

In the event of a go-around, with both flight directors off, LNAV will not automatically engage (at 50FT for manual flight or at 200FT with the autopilot engaged).

[main_dog]

Same thing on the 747-8 (and I believe B747-400 equipped with new FMC): for this reason after switching F/Ds off Boeing recommends switching PM F/D back on.

PS Despegue, are you Airbus? Different philosophy on AB, either both on or both off.

[Skyjob]

Also airline dependent...

Both off, then both on, recycles the system and it will not become active once more until so required (e.g. a MISAP)

[Cough]

In our airline... Both off to ensure the AT remains in Speed to avoid confusion.

[ACMS]

The last post is the correct one. #7 by Cough

The 777 crash in SFO was attributed to one on and one off wasn't it? The A/T stayed in HOLD ( at idle thrust ) and wasn't in SPEED mode.

Airbus also stipulate both on or both off for the same reason.

[flapsupdown]

That's incorrect.

If one on and one off, then yes, possible that the A/T is in a different mode to speed.

However, if both off, then one on, the A/T will be in SPD.

[ACMS]

Ummm ok but if one is "left on" then problem.

[flapsupdown]

If one is left on, the A/T mode will stay in the mode that it was in, whatever that may be (SPD/THR/HOLD...etc).

However, the instant both FDs are turned off, the A/T mode changes to SPD. When you then turn the PM's FD back ON, the A/T mode will stay in SPD

[FullWings]

Our FCTM used to have the on/off mix in it but it seems to have gone. It was overridden by the FCOM anyway in that respect.

I’m an advocate of all on or all off for the reasons others have posted. Yes, as soon as you get a mode change from TOGA on the GA, the flight directors will disappear but guess what? They come back on if you flick the switches! Amazing! What will they think of next...?

Also, more seriously, it depends on what guidance you require to maintain the desired flightpath. Are you visual, using basic (raw) data or requiring lateral and/or vertical guidance that can only be provided by the APFD/FMC? If it’s the latter, then you need to follow an appropriately programmed FD, especially with a specified RNP...

[Judd]

in the confusion of an unexpected go-around, someone will still have persistent FD guidance

Do you really need an FD to tell you what to do during a go-around? Isn't that the beginning of FD addiction? The FD is nothing more than an instrument flying aid yet pilots are so accustomed to staring fixedly at the FD they are lost without it.

[FullWings]

B777 DDG

22-11-10 Flight Director Systems

Interval: C
Installed: 2
Required: 0

May be inoperative provided approach minimums do not require their use.

There you go. The nightmare scenario!

[RAT 5]

Why do we switch the PNF's F/D on when flying visual,

I confess to being a B737NG guy, not B777, but I wonder if there re similarities. Firstly, is this a Boeing thing or a company SOP? If it's Boeing, then no idea: if company, then HOT is the source.

When a go-around is initiated, the FD will appear on both PFDs, regardless of the switch position. However, as soon as the first mode change occurs (LNAV or VNAV, most likely), the flight directors will disappear again if the switch is off. Thus, I imagine the PM's FD switch is turned on so that in the confusion of an unexpected go-around, someone will still have persistent FD guidance.

The first sentence is the same as B737NG, but any roll/pitch mode alteration from TOGA will cause FD pop-up bars to go AWOL. However, on NG if you switch both OFF then both ON you display FD in upper centre PFD with bars out of sight. Then on TOGA FD bars pop-up and DO NOT go AWOL at mode change. Is this a possibility on B777?

[vilas]

In visual approach FDs do not have guidance for RW threshold so you cannot follow them. And FDs should not be on when you don't intend to follow them. In Airbus they appear automatically on go around.

[RubberDogPoop]

Originally Posted by ACMS

The 777 crash in SFO was attributed to one on and one off wasn't it? The A/T stayed in HOLD ( at idle thrust ) and wasn't in SPEED mode.

Sort of...
At no stage were both FDs off at the same time, therefore the A/T remained in HOLD with FLCH SPD, & the PFs FD remained displayed throughout. Had they been cycled both OFF, one ON the unnecessary guidance would have been removed, and A/T reverts to SPD mode.

The NTSB recommendation was to have FDs - plural - remain off on a visual, as far as I can see the Boeing FCOM/FCTM remains unchanged.

As for no guidance on a visual, the theory is that the PMs FD reverts to sub-modes giving existing VS and azimuth so that they can monitor proceedings.

[ACMS]

? Sort of. I think we are in total agreement mate.

[RubberDogPoop]

Probably looks like semantics, just to be clear, at no stage were both FDs selected OFF. The PM simply turned the PFs OFF. For reversion to SPD mode they both have to be OFF at the same time, prior to the PMs being selected back ON.
The NTSB makes mention that the PM "loosely followed Asiana's informal practice"...
BTW I've mistakenly said the PFs was left ON above, not that it materially changes the outcome. No both OFF, no A/T wake up....

[ACMS]

Yes yes mate I get it..... never had an issue flying the 777 for 8 years either. Visual approach, BOTH F/D's off BIRD on. A/T in SPD mode.

Same on the Airbus.