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What Is The Purpose Of The Flight Director On AP?  
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Posted (8 years 10 months 4 days 18 hours ago) and read 18428 times:

I am trying to learn so forgive me, but as far as I can see the Flight Director on the autopilot pops up a cross on the artificial horizon display as to where the aircraft is going to pitch to but what else does it do? I would like to know what advantage it has other than that as I can't figure it out...I must be missing something....



J

[Edited 2005-11-19 21:41:44]

26 replies: All unread, showing first 25:
 
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 1, posted (8 years 10 months 4 days 17 hours ago) and read 18420 times:

Hello Julesmusician.

I believe one purpose of the vertical half of the "magenta coloured" flight director lines on the artificial horizon is to show when the aircraft's auto pilot is locked onto a GPS course line (which is shown on a MFD screen as a magenta line between two waypoints) and is tracking down the center of the course. If the aircraft's AP is not tracking down the center of the GPS course line, this is indicated to the pilots by how much the vertical Flight Director line is deflected left or right on the artificial horizon.

I hope that makes sense .... and that my info is correct. Big grin


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 2, posted (8 years 10 months 4 days 17 hours ago) and read 18414 times:

Sounds like the flight director is just a sort of compass pointing you in directions but has no effect on the actual command of the aircraft - well I am sure the pilots will correct us all  Wink

User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 3, posted (8 years 10 months 4 days 17 hours ago) and read 18404 times:

Yes, a flight director has no effect on what the airplane actually does. A flight director indicates how the airplane should be maneuvered to attain the desired parameters selected in the flight director control panel.

If you are flying on heading 360, with the flight director engaged in heading mode, and you turn the heading bug to 090, the flight director will move and command a bank to the right. It is up to the pilot or autopilot to follow the command.

A better example is when flying an ILS with the flight director engaged in approach mode. The flight director will command pitch and roll as necessary to maintain the localizer and glideslope. All a pilot has to do is match the flight director commands and the airplane will go right down the pipe, a pilot would never have to look at the HSI in this case (not recommended though).

There are two basic styles of flight director, the one with a vertical and horizontal bar, and the wedge type (I don't recall the official names for either). In the first style, the horizontal bar commands pitch, and the pilot tries to keep the pitch of the airplane matched with the horizontal bar. The vertical bar commands bank, and the pilot banks the airplane toward the bar until the bar returns to the center.

In the wedge type, the flight director is an inverted "V" that fits nicely on top of the airplane symbol (a flattish triangle type shape), and the pilot tries to keep the airplane symbol snugged up inside the "V".

In the airplane I fly, all the autopilot does is follow what the flight director commands, others may vary.



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User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 4, posted (8 years 10 months 4 days 16 hours ago) and read 18400 times:

So what would happen with the APPROACH switch on and the FLIGHT DIRECTOR switch off? If you say the APP switch follows the FD being on then if FD is off what will it do?

Thanks,

J


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 5, posted (8 years 10 months 4 days 16 hours ago) and read 18391 times:

Quoting Julesmusician (Reply 4):
So what would happen with the APPROACH switch on and the FLIGHT DIRECTOR switch off? If you say the APP switch follows the FD being on then if FD is off what will it do?

The autopilot (a sophisticated one, anyway) will still maneuver the airplane so as to fly what you have set. In most airline operations you are advised or even required to leave the FD display on so you can see what the plane should be doing as well as what it is doing. When hand flying, the usual advice is either fly the flight directors or punch them off, but don't "look through" them at the display beyond.

Quoting Mr Spaceman (Reply 1):
the "magenta coloured" flight director lines

Thanks to glass cockpits we now have a generation of straight male pilots who know what color "magenta" is.  Smile



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently onlineMir From United States of America, joined Jan 2004, 21626 posts, RR: 55
Reply 6, posted (8 years 10 months 4 days 16 hours ago) and read 18386 times:

Quoting SlamClick (Reply 5):
Thanks to glass cockpits we now have a generation of straight male pilots who know what color "magenta" is.

Ain't that the truth.  Smile

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 7, posted (8 years 10 months 4 days 16 hours ago) and read 18384 times:

Hi guys.

To expand a bit on the example I gave above, to get the autopilot to follow/track the magenta course line shown between two waypoints on your GPS (from A to B as entered), you would select NAV mode on the autopilot, and then the AP will command the aircraft to follow the GPS course line. Once the AP has captured the GPS course line and is following it, the vertical FD line on the AH will stay centered.

Or you can disengage the AP (or just the AP's NAV mode), and track the GPS course line manually by keeping the vertical FD line on the AH centered while hand flying.


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 8, posted (8 years 10 months 4 days 16 hours ago) and read 18379 times:

Now you got me because if I was tracking between two points in a flight plan on the GPS I would select GPS rather than NAV - I thought NAV was for following navigational beacons such as VOR etc...?

User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 9, posted (8 years 10 months 4 days 16 hours ago) and read 18378 times:

Hi guys.

Quoting SlamClick (Reply 5):
Thanks to glass cockpits we now have a generation of straight male pilots who know what color "magenta" is.

HaHaHa that's funny SlamClick. Big grin I can honestly say the only time I think about the colour "magenta" is when it's specifically addressed in aviation magazine articles about GPS systems.

Otherwise it would be the colour pink.


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 10, posted (8 years 10 months 4 days 16 hours ago) and read 18371 times:

Hi guys.

Quoting Julesmusician (Reply 8):
Now you got me because if I was tracking between two points in a flight plan on the GPS I would select GPS rather than NAV - I thought NAV was for following navigational beacons such as VOR etc...?

Remember that I'm referring to the NAV mode on the autopilot. You would select NAV mode if you want the autopilot to follow (Navigate along) the GPS course between the current waypoints.

A VOR station is tuned into and tracked To or From by using a navigation radio in your radio stack (if you have 2 NAV radios, you would enter the desired VOR's frequency - such as 113.3 - into either radio NAV 1 or NAV 2), and then use the VOR instrument's needle for your navigation info with reference to that VOR ground station.


I'm not trying to confuse you ... I swear!

Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 11, posted (8 years 10 months 4 days 15 hours ago) and read 18365 times:

If I place a waypoint or a destination into GPS and want autopilot to follow it I select the GPS selection on the switch. If I want to follow a radio beacon such as a VOR, I can tune the radio to it and select NAV on the switch on the autopilot. Of course you can follow a course to a VOR two ways, either by selecting it on the radio stack or asking your GPS to take you to the VOR. If you ask the GPS to take you to the VOR, then I select GPS on the autopilot....

User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 12, posted (8 years 10 months 4 days 15 hours ago) and read 18346 times:

Hello Julesmusician.

Quoting Julesmusician (Reply 11):
If I place a waypoint or a destination into GPS and want autopilot to follow it I select the GPS selection on the switch.

Can you show a photo of an autopilot that has a button or switch on it thats marked GPS? Now I'm lost because I've never seen a GPS button on an autopilot.

Here's the autopilot of a Boeing 777. Where's the GPS button?


View Large View Medium
Click here for bigger photo!

Photo © Craig Murray



Here's a photo of a light GA aircraft's autopilot and some info about it.

"For single-pilot instrument operations in light aircraft, there's only one flight control system that borrows sophisticated technology from the flight control systems developed for helicopters and high-end business jets - the Bendix/King KFC 225 Autopilot/Flight Director."



Where's the GPS button on the AP?

Quoting Julesmusician (Reply 11):
If you ask the GPS to take you to the VOR, then I select GPS on the autopilot....

If you enter a VOR station into a GPS unit, it becomes just another waypoint (like a Lat/Long marker), and if you want your autopilot to track the GPS's "magenta" course line between that VOR and another waypoint ..... you push the NAV mode button.




I'm beginning to feel like I'm flying on instruments right now!  wink  We're obviously not understanding each other.  Confused Could you see us being a flight crew!!!  Silly


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 13, posted (8 years 10 months 4 days 15 hours ago) and read 18343 times:

Just look at my first picture - there is the GPS button!  Wink

User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 14, posted (8 years 10 months 4 days 14 hours ago) and read 18336 times:

Hello Julesmusician.

Quoting Julesmusician (Reply 13):
Just look at my first picture - there is the GPS button!

OK, I see that toggle switch marked GPS. Thanks for pointing that out.

Now I'm confused, so please forgive me, but I'm gonna wait patiently on the sideline for a pro to answer your questions and hopefully explain what I'm confused about too!

The expression ... "The Blind Leading The Blind" comes to mind now. I'm only speaking for myself though.

Edit: I just noticed that your picture with the GPS switch is from MS FlightSim. What aircraft is that?

Chris

[Edited 2005-11-20 00:52:15]


"Just a minute while I re-invent myself"
User currently offlineJulesmusician From , joined Dec 1969, posts, RR:
Reply 15, posted (8 years 10 months 4 days 14 hours ago) and read 18325 times:

I am sure the pilots will answer. Basically the 737 - 400 allows you, according to flight sim, to have a VOR or another radio beacon in the radio stack and you can select it via NAV on the autopilot. If you fancy letting the gps do the navigating then you can mark a waypoint in the gps and select GPS on the autopilot and it will take you to it. Whether this is how the real world works, I am sure a pilot will tell us.

User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 16, posted (8 years 10 months 4 days 14 hours ago) and read 18310 times:

Not quite. I don't fly the 737, but Boeing's FMS are pretty much all the same.

You can select the VOR on the RAD/NAV page and then select VOR on the ND. However, in reality, if you use the FMS to proceed direct you go to the FMS position, which is the IRS position into the FMC updated with GPS.

There really is no way to use the VOR to navigate unless you just go to the heading mode, and in the RAD/NAV page and put the appropriate course in the course selection.


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 17, posted (8 years 10 months 4 days 13 hours ago) and read 18294 times:

Hello Julesmusician.

OK, we've been talking about two different buttons. HaHaaaaaaaaa!

I've been talking about the NAV mode button on the AP & you've been talking about the Master NAV/GPS switch for the aircraft's navigation systems.

When I fly my simulator (the Learjet 45 for example), and I want the autopilot to track my GPS course, I need to have that master toggle switch on the GPS setting and the AP on NAV mode.

Here I'm arriving at St Paul Downtown Holman Field (KSTP) in Minnesota. The active was runway 32.



Then when I'm ready to fly a pattern during my arrival and final approach, I need to flip that toggle switch up to the NAV setting, and then I can select HDG mode on the autopilot to use the AP to steer around the airport toward the final approach course. Next when I have my ILS needles centered (or close to it), I select the APP mode on the autopilot and let the Learjet fly the approach down to about 400 feet AGL where I disengage the autopilot & auto throttles and hand fly the jet onto the runway.

Here I'm intercepting the ILS for Rapid City Regional's runway 32 (KRAP) in South Dakota ..... and I'm obviously to low!



Thanks to the autopilot's Approach Mode (& auto throttles), I saved the approach and did a smooth landing. Big grin





>> I also wonder if these cockpit switches work the same way in a real Learjet or airliner?


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlinePihero From France, joined Jan 2005, 4445 posts, RR: 76
Reply 18, posted (8 years 10 months 4 days 13 hours ago) and read 18286 times:
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Quoting Julesmusician (Thread starter):
as far as I can see the Flight Director on the autopilot pops up a cross on the artificial horizon display as to where the aircraft is going to pitch to but what else does it do?

A Flight Director tells the pilot A/the direction and B/the amount of pitch (from the horizontal bar) and roll (the vertical bar) he needs to apply in order to intercept or come back on, or maintain a trajectory he has selected. That trajectory can be anything programmed on the FMS or requested on the Flight management panel .
That very long sentence means that in general, it should be always centered, regardless of the bank or attitude indicated on the same instrument (called PFD for primary flight display).
SamClick says it rather well :the PFD tells you what the aircraft is doing - on the artificial horizon bit- and what it should be doing -by a reading of the FD command bars.

Why use the FD when you are on autopilot ? It is a way of monitoring what the autopilot does and you would say "that's silly because they're doing the same thing " but in fact they don't :In a very simplistic manner, the autopilot does integral calculus whereas the FD is an ace at differentials.( before you start flaming, I stress the "very simplistic" part ).

I here insist on this sole use of a FD :it gives piloting commands. Nothing else.

Now the NAV bit.
On a modern airliner, believe it or not, the main navigation system used is the GPS. If the GPS info is not available, we revert to area navigation by means of an Inertial Reference System updated with VOR-DME or TACAN ground stations. So in the western world, VOR to VOR routings are no longer our daily meat.
Spaceman, you won't find a GPS switch on that T7 panel as the GPS info would be on the FMS display on the console and somewhere an indication of "GPS PRIMARY".What you have is an "LNAV" pushbutton, Boeing's philosophy for separating lateral LNAV and vertical VNAV navigation.
It doesn't alter the fact that en-route, you would like to follow the flight plan you stored in your FMS ; then you make it current and you just press the NAV or LNAV button. And that's all.
Hope it helps.



Contrail designer
User currently offlineDeltaGuy From , joined Dec 1969, posts, RR:
Reply 19, posted (8 years 10 months 4 days 12 hours ago) and read 18282 times:

Quoting SlamClick (Reply 5):
Thanks to glass cockpits we now have a generation of straight male pilots who know what color "magenta" is

I had a very wide M88 Captain once tell me that you are to only refer to it as a Magenta line/bar...it is never pink.

Quoting Ralgha (Reply 3):
There are two basic styles of flight director, the one with a vertical and horizontal bar, and the wedge type (I don't recall the official names for either).

I believe the "needles" version is double cue, and the inverted-v is single cue..IIRC.

DeltaGuy


User currently onlineStarlionblue From Greenland, joined Feb 2004, 17039 posts, RR: 66
Reply 20, posted (8 years 10 months 4 days 12 hours ago) and read 18276 times:

Quoting Julesmusician (Reply 11):
If I place a waypoint or a destination into GPS and want autopilot to follow it I select the GPS selection on the switch. If I want to follow a radio beacon such as a VOR, I can tune the radio to it and select NAV on the switch on the autopilot. Of course you can follow a course to a VOR two ways, either by selecting it on the radio stack or asking your GPS to take you to the VOR. If you ask the GPS to take you to the VOR, then I select GPS on the autopilot....



Quoting Julesmusician (Reply 15):
I am sure the pilots will answer. Basically the 737 - 400 allows you, according to flight sim, to have a VOR or another radio beacon in the radio stack and you can select it via NAV on the autopilot. If you fancy letting the gps do the navigating then you can mark a waypoint in the gps and select GPS on the autopilot and it will take you to it. Whether this is how the real world works, I am sure a pilot will tell us.

The confusion is due to the fact that the "stock" 737-400 in MSFS has a simplified cockpit, including a simplified autopilot. For a "real" 737-400 cockpit in MSFS, you need Dreamfleet's add-on (unfortunately only for MSFS 2000/2002) http://www.flight1.com/products.asp?product=ga737. As you can see from the pic, the autopilot panel is quite different (and more accurate) than the one in the stock 737-400 that comes with MSFS. It also behaves like the real thing unlike the stock one.



For comparison, here is your original pic (hope you don't mind the bandwidth stealing):


And a real plane:

View Large View Medium
Click here for bigger photo!

Photo © Christian Dal Mas




For a reasonably accurate (but still not real) description of the 737-400 autopilot, refer to Dreamfleet's manual page: http://dreamfleet2000.com/Downloads/737_manuals_ops.html



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 59
Reply 21, posted (8 years 10 months 4 days 12 hours ago) and read 18276 times:
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Quoting SlamClick (Reply 5):
Thanks to glass cockpits we now have a generation of straight male pilots who know what color "magenta" is.



I first used the term when referring to the color on VFR sectional charts.




2H4





Intentionally Left Blank
User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 22, posted (8 years 10 months 4 days 11 hours ago) and read 18263 times:

Quoting DeltaGuy (Reply 19):
I had a very wide M88 Captain once tell me that you are to only refer to it as a Magenta line/bar...it is never pink.

Gender insecurity...



09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 23, posted (8 years 10 months 4 days 6 hours ago) and read 18225 times:

Lets put it this way.
A Flight Director uses the Pilot as a Servo to Manuvere the Aircraft as per Instructions provided.
regds
MEL



Think of the brighter side!
User currently onlineStarlionblue From Greenland, joined Feb 2004, 17039 posts, RR: 66
Reply 24, posted (8 years 10 months 3 days 23 hours ago) and read 18174 times:

Quoting HAWK21M (Reply 23):
A Flight Director uses the Pilot as a Servo to Manuvere the Aircraft as per Instructions provided.

Well put! The difference is that the flesh servo is less accurate than the mechanical one Big grin



"There are no stupid questions, but there are a lot of inquisitive idiots."
25 Post contains images HAWK21M : Agreed.Still We'll never fly with a Mechanical Pilot in control but would prefer a Human one BTW...Where did the term Flight Director originate from.
26 Zeke : Fairly simple, With the autopilot on, the flight director displays the commands from the flight management computer and autopilot control panel of wha
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