Flight Directors

[Lump Jockey]

As a non pilot, I was just wondering what help the FD gives you as an aid in flying? Do they show you the attitude you should achieve or something? Apologise for my ignorance here! Also what's AOC short for!?
TIA

[OBK!]

Your half way there! The flight director is driven by the automatic flight direction system (AFDS) and basically, whatever you command on the autopilot, it will follow. You can follow it (well, some airlines say you gotta follow it for the smoothest most efficient ride etc etc) to get what you have selected on the autopilot. So you set 10,000ft, and heading 360 and you are 9000ft and 300 it will command an up attitude, and right turn...but it's surely not as simple as that, all different stuff about performance/config of the airctraft are taken into account.

AOC i think means Air Operaters Certificate...just a guess, I heard it somewhere before, not sure what it's for. A certificate to operate I guess?:rolleyes:

[Capt Wannabe]

From what I remember the flight director gives the commands independatly of the autopilot. It is quite possible to use a FD without an AP, but if required an AP will follow the commands of the FD.

[OBK!]

Yeh something like that. There's a switch for both anyway :)

[Tinstaafl]

The Flight Director (FD) provides steering cues that are displayed on the Attitude Indicator. It's usually either in the form of 'V bars' or 'Cross hairs'. These steering cues are in response to deviations away from some specified datum eg altitude, heading, pitch attitude/speed, navigation instruments etc etc

When the FD is being used, the job of the pilot is to make control inputs that keep the attitude indicator's a/c symbol matching the position of the Flight Director's V-bar/cross hair symbol. This is instead of interpreting the flight &/or nav instruments to achieve the same result.

If fitted, an autopilot replaces the pilot in making the control inputs.


Note: Even while following the FD commands the pilot still crosschecks its commands by comparing them to what would be done without the FD.

[Pilot Pete]

Just a point of order, I don't want to sound pedantic but;

Tinstaafl wrote
If fitted, an autopilot replaces the pilot in making the control inputs

I would tend to disagree with the literal wording, which perhaps is not the meaning desired in that the pilot is not replaced by an autopilot, he just controls the a/c through an MCP (master control panel, on the Boeing) instead of through the column/stick.

Another point which may be of interest to the layman is that we use the MCP to control the F/D which the autopilot will follow. If however we wish to hand fly the a/c but still use the F/D then someone has to still put the required commands into the MCP in order to get a correct F/D display. This increases the cockpit workload as the PF will be concentrating on hand flying and not putting his own commands into the MCP whilst the PNF has to take on this job as well as the R/T and monitoring. It is strongly recommended to always have the FD giving a sensible display when hand flying for obvious reasons, but even if you choose to switch it off and fly completely 'raw data', again, it is still worth keeping the MCP inputs up to date as a reminder of clearances for altitude, heading etc just in case you wish to turn it back on again.

One last point that springs to mind is that the FD gives you an indication of the required control inputs to rectify any deviation from the selected parameters (in the MCP). If you follow that input, as your error starts to rectify obviously a new indication from the FD will occur back in the other direction as you reach the desired parameters commanding you to now maintain these parameters. This can lead to pilot induced oscillation around the datum as the pilot 'chases' the FD. This is why it is important to 'nail' the FD exactly in the first place and if a deviation occurs catch it quickly, or look through it and fly a known pitch attitude and power setting to let things settle. It sounds harder than it actually is! I often prefer to switch off the FD when hand flying an approach, but this can lead to a CRM breakdown if the other pilot still has his FD on (and with my hand flying I appear to be deviating from the FD commands!)

anyhow, hope that was of some interest.

PP

P.S. AOC as already stated is an Air Operators Certificate and is what a carrier requires from the authority (The CAA in the UK) to operate a/c for public transport (like hire and reward with minicabs). It takes quite a bit to get it issued in the first place and is not just a case of applying, requiring a suitable structure and various regulations to be followed.

[quid]

Also, in some a/c, the Flight Director and the Autopilot have different gain programming. In the early stages of the approach, it may seem that the autopilot is not flying the F/D commands. As the approach continues, they become closer and closer.

[Ennie]

It's an excellent flying aid, but it's always nice to switch it off and fly raw data!

[max_cont]

Pilot Pete, MCP on a Boeing aircraft stands for Mode Control Panel.

Sorry to be pedantic…but I couldn’t resist.;) ;) :D

[Pilot Pete]

Yes indeed. I must have been thinking of the wife at the time.................!

PP:D