Split Cues vs Inverted V

[Guest]

This is a really small question but it is bugging me a bit. Why do some airlines configure their Boeing aircraft with Inverted V (that weird looking one where a purple V was put into photoshop, stretched out too much and flipped 180 degrees) flight directors instead of the Split Cues? (The two lines) Or vice versa. 

I think that it is easier to fly the FD with the split cues as you can (in my testing) follow the FD more precisely than in other aircraft. 

Could anyone provide some insight as to why there are two variations to the FD?

I presume that the Inverted V was to keep commonality with another aircraft?

[richjb2 195]

Zach,

You have just entered into one of the age-old controversies among real pilots, which is better the split-cue or single cue FD.  

The split-cue or crossbars have been a favorite of the military, especially tactical jet fighters.  The dual cue FD was invented in the early 60's to address a series of early transport jet upset incidents, that highlighted in this video:

The single cue, or V-bar flight director provides the pilot with an immediate cue of exactly where to place the aircraft in roll and pitch.  All you have to do is fly formation with the V-bar, keeping just a little bit of space between the airplane symbol and the V-bars. 

The split cue or cross-bars FD has the advantage of allowing independent following of flight director commands.  This advantageous when you might want to follow pitch (e.g. altitude hold) commands while maneuvering the aircraft, for example during a circling approach. 

From what I can tell, most of the airlines are now settling on the split cue, cross-bar FD. Southwest (SWA) recently reset their B737 fleet to use the cross-bars.  They were one of the holdouts in the US still using the V-bar flight director. 

Most business aircraft use the V-bar flight director.  

Hope this helps,

Rich Boll

Wichita, KS. 

 

 

 

[downscc 1,327]

On 8/20/2017 at 6:02 PM, richjb2 said:

The single cue, or V-bar flight director provides the pilot with an immediate cue of exactly where to place the aircraft in roll and pitch.  All you have to do is fly formation with the V-bar, keeping just a little bit of space between the airplane symbol and the V-bars. 

The split cue or cross-bars FD has the advantage of allowing independent following of flight director commands.  This advantageous when you might want to follow pitch (e.g. altitude hold) commands while maneuvering the aircraft, for example during a circling approach. 

Good answer Rich, and exactly why I like the split-cue.  Besides learning instrument flying before such things as HSI with FD gauges, I learned the basic six pack and flying the ILS on a CDI gauge.  The FD cross bars are analogous to the ILS LOC/GS deviation indicators, and as you pointed out one axis can be give more priority.  I find this especially useful in climbing departure turns where I prefer to set my own pitch instead of chasing the pitch bar and use the roll bar to guide me through the turn.  It make for a much smoother hand flown departure.  Of course, I am not ignoring the pitch cue but I am using it along with speed cues.

[CW46 101]

Back in the day my first FD experience was single cue and all other aircraft I flew there after were also equipped that way so I always found it to be a natural presentation. As a sim instructor I found the majority of European clients would choose split cue, North American clients single cue. What ever your first exposure was to a FD probably dictates what you use today.

[jfriz 27]

Mine was the single cue, still prefer it today.

Jerry Friz

[Paul_Smith 92]

It really is the difference between a digital clock showing 24 hour time and one showing AM/PM. It is exactly the same information and one axis can be given priority with a V cue just as easily as with a split cue, and both can give axis priority just as easily as the command bars of an analog ILS. They all just indicate where the FD thinks you should go but the FD is only a navigator, you are the pilot.

[xkoote 57]

Hi,

I flew for 9 years on a mix of split and single cue MD-80's. And while I agree on the fact that with the split cue you can follow one axis whilst giving lower priority to the other, I find it also detaches you from actually flying. You are basically starting to focus solely on that damn cross. I liked the V-Bar because I felt what it told me was. "Listen, you're hand flying. Never mind that 50 fpm or that half a degree of bank and fly the thing". I could more easily see through the V-bar and actually fly, using its inputs as kind advice. The cross tended to make me a slave to it, while it already has a slave. The autopilot.

 

My 2 cents....

[kevinh 409]

Back in the days before glass cockpits, Collins ADIs used vee bars and Sperry ADIs used cross bars. Although they look very different they actually display exactly the same information using the same FD inputs. Vee bars show roll and pitch separately too but because the bars move together it doesn't look like it. Neither format is better than the other, preference is mainly down to what you are used to.