V-bar FD display during partial faults

[Hardy Heinlin]

Hi all,

does anybody know how the V-bar display behaves when just the roll or just the pitch command fails?

The crossbar display simply hides the vertical or the horizontal bar. So the pilot can see that the respective axis is not perfectly centered but inoperative. How can this information be communicated with this V that integrates both axes? It's either all or nothing.

I guess I asked this question many years ago; I can't remember the answer, if there was any at all :-)


Thanks,

|-|ardy

[Mariano]

Hi, Hardy.

As per the NW FCOM, " An FD failure, in either pitch or roll, causes the command bars to disappear."

I will send pictures shortly.

Best regards,

Mariano

[Mariano]

Here:

https://1drv.ms/i/c/da890b87be2c6bc4/IQDZHxtPYaVySIFQi4dSOMTRAVuojiNNsb3eWBuilDGrRCk

Best regards,

Mariano

[Hardy Heinlin]

Hi Mariano,

thanks. Nice, this behaviour is modelled in PSX.

It's strange that they wrote the word "bars" in plural since it's a single V-bar. But perhaps they meant the two V-bars on the two PFDs. Or it's a "copy & paste" from a standard manual and they forgot to write it V-bar specific.


Regards,

|-|ardy

[Mariano]

I assume plural because the bars are split the apex? But, more likely, copy and paste.

While on this subject, yesterday I came across this article. I haven't read it yet, but I saved it to my list for my next commute/layover. I did notice that it has PSX screenshots, though.

https://aviationtroubleshooting.blogspot.com/2012/07/af-447-flight-director-with-v-bar-would.html?m=1

Best regards,

Mariano

[Hardy Heinlin]

Yes, that article uses pictures from this forum thread from 2011. The screenshots are from an early alpha version which were not 100 % accurate at that time:

https://aerowinx.com/board/index.php/topic,873.msg8511.html#msg8511

In the released PSX version the white fixed triangle at the top has a lightgray filling, the green "30/..." label by the speed tape does not overlap the red tape, and the FD bars are not that thinn :-)

Quote from the article:
"The V-bar presentation is so favored by pilots that you almost never see a split-cue flight director anymore."

NWA and Delta (who bought NWA aircraft) were the only 744 operators that used the V-bar, as far as I know. So it turned out to be the other way round.

But I think it's true, as stated in the article, that the V-bar is useful for great bank angles, and the crossbar is better for small bank adjustments. I, for one, cannot see small bank commands on the V-bar unless I move my eyes to the V-bar wing tips left and right, in order to see which side goes up and which goes down. In the center I can hardly see any small bank angles. In my opinion, instrument scanning is easier on the crossbar because I see every information at the same place in the center of the attitude display.

The V-bar is certainly useful on aircraft types that are permanently flown at great bank angles. NWA hired a lot of fighter pilots, if I recall correctly. That might explain why they preferred the V-bar :-) NWA also had those strange flare tones instead of the aural height callouts. I think they just wanted to stick to the old features they were used to. Also typical for NWA: On rollouts they sometimes kept the nose up as long as possible, for aesthetical reasons, I think. NWA was very special :-)


Regards,

|-|ardy

[G-CIVA]

NWA and Delta (who bought NWA aircraft) were the only 744 operators that used the V-bar

Add to that very small list Air China.

[Mariano]

Same here. I find the V-bars more intuitive but less precise (especially for small corrections). I fly both types in PSX. The V-bars have more of a classic feel.

American Airlines used V-bars in their 767s. Not sure about their 757s, but very likely. I think El Al still uses V-bars (even on the 787); perhaps also fighter pilots-related?

Regards,

Mariano

[Will]

On the type I flew, my company had most aircraft outfitted with V-bars, but a few with dual cue flight directors. So I have flown the same aircraft with both. I felt the V-bars were better in normal line ops. Of course, this was an easily maneuverable turboprop and not a widebody; perhaps that makes a difference. I spend most of my time in PSX using the V-bars. I'm happy PSX has the option though. :-)

[Hardy Heinlin]

Add to that very small list Air China.

And I forgot El Al ... :-)

[dhob]

UPS 747-400s and -8s used the single cue FD (V-bar) until 2019.

[Hardy Heinlin]

On all 744s and 748s or just on those that were bought from Delta etc.?

[Cbf]

There are flight deck pictures on Airliners:
- N673US 747-451 Delta former Northwest (Dated 2010): V bars
- N661US 747-451 Delta former Northwest (Dated 2015): cross bars
Dont know about the flare tone...

[jawomba]

There are a few pictures on airliners.net showing different Delta Airlines 744 with cross bar FD (roughly from 2015 on).
- N670US
- N669US
- N666US
- N661US
I gues it came with a retrofit for Delta 744.

Delta Airlines N313SQ came from SIA, I would expect cross bar FD on this plane, but I found no picture.

I think there are no UPS 744 from Delta but I guess they have the v-bar FD only on those they ordered from Boeing.
They have other from Cargolux and EVA-Air with X-bar FD.

Best regards,
Jan

[Hardy Heinlin]

- N669US

That situation looks strange (on EH-FP). Only the pitch bar is shown, yet only the roll mode is annunciated (LOC).

[jawomba]

Could this be part of an APFD adjustment test via the CMC?

[Hardy Heinlin]

There's no engineer in sight :-) Maybe the vertical bar is hidden because the photograph was taken right in that moment when the CRT beam was about to redraw exactly this screen area. But that would be a funny coincidence.

Here's a photo I shot on the jump seat. It shows the partial redrawing effects. It also shows that the magenta stuff is generated by blue and red beams. The photo was taken in a moment after the red FD was drawn and shortly before the blue FD was drawn.

[jawomba]

I tried to set up PSX in the same way. PSX shows rather the same behavior, see screenshot

There are three things that seem to be different, in the picture on airliners.net you can see:
1) GS in ND is 1 (in PSX it shows 0)
2) no magenta heading select line in ND
3) no yellow-crossed-out LOC in FMA on the PFD (in PSX LOC is crossed-out)

All is more reasonable in PSX.

Best regards,
Jan

[Hardy Heinlin]

Ah, I forgot I programmed the same after-landing FD behaviour in PSX :-)

The remaining 1 kt GS is a normal IRS inaccuracy.

The hidden HDG line: Maybe there is another condition for this aside from LNAV being engaged. Engine shutdown or something.


Regards,

|-|ardy

[jawomba]

Thank you for your feedback, amazing picture that shows the moment after the red FD was drawn.

Cheers Jan