Flight Director

[goingmach_1]

Can anyone explain the differences between a single cue, and command bar flight director?

[PanEuropean]

The difference is how the guidance is presented to the pilot - either as an X-Y co-ordinate, or as a single symbol.

It's kind of hard to explain in writing - I will try to find a photo showing both versions and post it.

The actual guidance presented is identical on both, it is just the manner in which it is visually portrayed that is different.

Michael

[PanEuropean]

Here is an illustration of a single cue presentation and a cross-pointer presentation. This is an illustration of an electronic display, and with most electronic displays, the pilot can choose the preferred configuration. Such a choice is not available on electro-mechanical instruments.

Michael

[goingmach_1]

Thanks for the quick reply.

I was told once that the single cue only displays the posistion of the localizer, and the posistion of the glide slope. In other words, if you are on a intercept, and approach armed, to intercept the localizer which is on one your left hand side, when the flight director captures the loc, and the beam is still to the left, the single cue flight director will show to the left. As the aircraft flies through the localizer, the single cue flight director will follow the beam. So, if its a 90 degree intercept, not good from a pilot point of view, as the aircraft flies through the beam the single cue will follow the beam. Versus the command bar(s), which when armed, will command a turn to best intercept and fly the beam.

So in the above case, at a 90 degree intercept, not good from a pilot point of view, the command bars will command a turn to to the right to interecpt the beam and stay on centre. Same goes with the glide slope.

I have only once flew the command bars on a old Sperry equiped Falcon 20 and everyone was lost to how they worked. Still wondered today as I fly a state of the art Corporate Buzzard but it has the single cue. I know the big guys have command bars and was hoping to get a understanding of how they work.

Thanks

[PanEuropean]

Uh, to the best of my knowledge, the flight director will provide the same guidance to the pilot regardless of which display format (single cue or cross-pointer) is selected.

The steering commands are coming from the flight director computer, the only difference between the two presentation formats is how those steering commands are visually presented to the pilot.

Michael

[FOX69]

Dual cue (command bars) is a more sophisticated system. It offers 2 independent command bars, one for pitch, and one for roll. The pilot is able to follow both, or just one. IE if a pitch mode was disengaged there would be no pitch bar, but still a roll command bar.

[fanspeed]

Level of sophistication is the same. Both are telling the pilot the sameinformation just in a different format.

[JohnnyHotRocks]

Level of sophistication is the same. Both are telling the pilot the sameinformation just in a different format.

exactly...just two ways of presenting the same info.
On our airplane, you can switch between the two with the click of a button

[nimbostratus]

I prefer single cue for almost every part of a flight. Unless there is a visual circuit involved, then I flip over to cross point and keep the horizontal bar on the horizon and ignore the vertical. Keeps you perfectly at circuit height with just the most basic scan. I find the single cue pretty much useless in this situation. It is giving you the same info but it is muddled because the cue is always making me want to initiate a turn.

Nimbo.

[Panama Jack]

PanEuropean, I am curious to know on what type of aircraft that you have experience with the pilot can select either display. Is this on corporate stuff?

On the airline equipment that I have experience with, to my knowledge it was the operator who could change the display but this was not a simple push-button operation for the pilot. In any case, once the airline favored one type of display or another, it became an SOP issue.

I thought I had the "moustache" (single-cue) and "cross bars" (double-cue) flight directors all sorted out, when I recently had to learn a new presentation on the Embraer E-Jets-- a small, magenta "diamond." Still a challenge.

[UKPilot]

PanEuropean

I thought I had the "moustache" (single-cue) and "cross bars" (double-cue) flight directors all sorted out, when I recently had to learn a new presentation on the Embraer E-Jets-- a small, magenta "diamond." Still a challenge.

Is that like the Track/FPA on the airbus? The two airlines I've flown for on the bus have it as SOP to turn the Flight Directors off if you're going to use Track/FPA I think because it's quite confusing. Is that presentation always used on the E-Jets?

[turbo-prop]

Proline 21 allows the pilot to change the flight director.

[Panama Jack]

The presentation you get on the E-jets looks identical to the Track/FPA on the Airbus and is called the "Flight Path Angle (FPA)" on the Embraer. Takes a little getting used to, especially since on the Airbus we also dumped the FD whenever we flew in Track/FPA mode yet on the Embraer it is always flown like this.

The flight director is then just a little magenta diamond (with wings) that you need to put into the centre of the green FPA circle (which looks faint in the picture below). I liken it to trying to get a gun's boresight on a target. A picture is worth a thousand words:




Well, what I could not show was the magenta diamond (which is commanding to increase pitch and bank left) to be put into the centre of the FPA circle. As the aircraft is banked left the magenta diamond will come towards the centre of the ADI.

A lot like playing a video game.

[nimbostratus]

The Primus 1000 allows you to switch between SC and CP. It also has an FPA feature, straight off the HUD of an F-16 I was told. Aircraft I know of that are equipped with the Primus 1000 are the Citation V Ultra and the Lear 45, not sure what else has it. It's getting old now, the newer stuff is still greek to me.

Nimbo

[PanEuropean]

I am curious to know on what type of aircraft that you have experience with the pilot can select either display. Is this on corporate stuff?

Hello Jack:

In my case, it is a Series 400 Twin Otter (photo below).

You are correct with your observation that most air carriers pick one of the two presentation formats and establish that as the standard for the fleet. In the case of the Honeywell Primus Apex avionics suite used in the new Twin Otters, the ability of the pilots to select the presentation format is controlled using an options and configurations file. The organization purchasing the aircraft can specify that they want to permit the pilots to choose the presentation format (in much the same way that the pilots select inches of mercury or millibars for display of altimeter setting), or they can specify that one of the two formats is used and the pilot is not presented with a configuration choice.

To be really precise, the choice is not "what the flight director looks like", the choice is "what the aircraft symbol on the attitude indicator looks like". If the wedge-shaped "single cue" aircraft symbol is selected, the flight director cue will appear in single cue (chicken-legs) format. If the cross-pointer aircraft symbol is selected, then the flight director cue will appear as two lines, one vertical and one horizontal.

My experience in the industry is that most private and corporate EFIS installations permit the pilot to choose the desired presentation, most air carrier and military installations are set to a single format that is consistent acrosss a fleet.

I've attached a page from the Honeywell Primus Apex Pilot Guide for the DHC-6 Series 400 that explains the two choices.

Michael

DHC-6 Series 400 Flight Compartment


Configuration Choices for Aircraft Symbol (determines Flight Director presentation)

[Joe Blow Schmo]

The presentation you get on the E-jets looks identical to the Track/FPA on the Airbus and is called the "Flight Path Angle (FPA)" on the Embraer. Takes a little getting used to, especially since on the Airbus we also dumped the FD whenever we flew in Track/FPA mode yet on the Embraer it is always flown like this.

The flight director is then just a little magenta diamond (with wings) that you need to put into the centre of the green FPA circle (which looks faint in the picture below). I liken it to trying to get a gun's boresight on a target. A picture is worth a thousand words:




Well, what I could not show was the magenta diamond (which is commanding to increase pitch and bank left) to be put into the centre of the FPA circle. As the aircraft is banked left the magenta diamond will come towards the centre of the ADI.

A lot like playing a video game.

Interesting. What exactly does the FPA tell you? Is it telling you the location of the vertical/horizontal track you're supposed to be on? The FD is commanding an increase in pitch and a left turn. It looks like the FPA is also commanding a left turn and an increase in pitch (although less of a pitch increase than the FD). If you put the FD in the FPA circle will both then be on the wing bars?

On the Boeing we have a FPV (flight path vector) that shows the actual aircraft track in both the vertical and horizontal planes. It's completely indepedent from the FDs. If you're flying straight and level with no wind the FPV will be sitting on the horizon in the middle (while the FD will be commanding whatever nose up pitch is required to maintain level flight). If you had a right crosswind it would be on the horizon but offset to the left to indicate the actual track was left of your heading. If you were on a 3 degree glide path the FPV would sit 3 degrees below the horizon. It's great for flying circuits and visual approaches. It doesn't give any indication of desired state though, just actual.

[PanEuropean]

...Is it telling you the location of the vertical/horizontal track you're supposed to be on? The FD is commanding an increase in pitch and a left turn. It looks like the FPA is also commanding a left turn and an increase in pitch (although less of a pitch increase than the FD)...

Joe:

Keep in mind that many of the illustrations that you find in manufacturer documentation or in training materials (likely where Jack got his illustration from, certainly where I got my illustrations from) do not present indications that are actual "in flight" indications. For example, in Jack's illustration of the Embraer flight director, the localizer and glideslope indications are perfectly centered, but the magenta diamond is commanding a significant pitch up and turn to the left, and the lateral acceleration indication (basically a slip-skid indication) shows a huge slip or skid. The only circumstance I could imagine this to be valid in would be the opening scene of "2001 - A Space Odessey" where the spaceship is docking with the rotating space station in the midst of a solar windstorm...

I wrote the Pilot Guide for the Honeywell Primus Apex suite in the DHC-6 Series 400, and during the course of writing it, I was constantly running up aginst this problem - a single image of a compound presentation (e.g. the whole attitude indicator) could often confuse the reader. The only way I could get around this was to first illustrate each component within the compound presentation on its own (for the purpose of identification of the individual component), then, to provide a chapter in the manual that presented a sample flight (an actual flight) from start to finish, to show how all the individual components worked together and related to each other.

Michael