Flight Director versus ILS Indicator

[ryanf]

Hi All,

quick question - not sure if its an airbus thing or a pm thing;

when doing an ILS approach, do the flight director needles simply mirror the ILS indicators or is there some more intelligence there?

e.g. If I am above the glideslope, will the FD first command a pitch to re-intercept and then before I actually cross the glide slope, begin commanding pitch changes to bring me onto the glideslope at the correct pitch?

Hope that does not sound too convoluted....

thanks,
Ryan.

[Jackpilot]

The FD always shows you what to do to comply with whatever is dialed on the MCP.
On final I must say that I never look at the FD and instead concentrate on the ILS indications....which does not answer your question by the way...Oh well..!

[ryanf]

Thanks Jackpilot.

If anyone else happens to notice what goes on in their setup, I would be interested to know.

/Ryan.

[Michael Carter]

The only time I used the flight director is when the weather is at it's worst. It's usually just in my way in other cases.

I follow the HSI.

[Trevor Hale]

Hope that does not sound too convoluted....

thanks,
Ryan.

Sorry to tell ya but it does LOL. I think I get what your saying but here is something you should try. Remember Rule #1 with flightsim... Never be above the glide slope. Never, never never. Always be below the glide slope and fly into it. The flight director for me is a tool that points the way to the path programmed into the FMC, or points to the path for the heading selected on the MCP. I have never seen the Flight director assist with Glide slope before, but that could just be because I have never used it for that purpose.

Maintain an altitude below the glide slope. Get set up on the LOC and then fly through the glideslope and begin your decent. If the FD is going to help you it will only help you once your all set on the LOC and ready for decent with the G/S in LOC Mode.

Does that make any sense?

Trev

[ryanf]

Hi Trevor,

you got my drift and I got yours!

I had set myself up for an approach below the glideslope and intercepted it on autopilot.

However, I drifted above it when I switched to manual flying - need some practice! Maybe the FD was trying to get me below the glideslope so I could reintercept it from below.....

Is there something peculiar in FS about being above the glideslope?

cheers,
Ryan

[3202b]

Is there something peculiar in FS about being above the glideslope?

cheers,
Ryan

No it's actually a real world thing, FS will allow you to establish above the GS perfectly everytime but in the real world there is a slight possibility of capturing erroneous glideslope signals where the aircraft thinks it is established on a glideslope when in fact it isn't. This is due to the way Glideslopes are calibrated at airports where anything steeper than a 3 degree glide path (could be more depending on the airport) is usually inaccurate. Also you should capture the Localiser before descending on the GS, not doing so can also cause false glideslope capture.

Flight directors on modern glass aircraft will guide both the Localiser and Glideslope and command pitch up and down if your below or above. So yes there is some intelligence there - the director will detect if you are below or above and command the pitch bar accordingly in response.

[dodiano]

Actually the Flight directors are basically mandatory on the Airbus I mean they are the best tool you have to fly precise and fuel efficient... Since virtual fuel is cheap up to you guys if you use it or not of course... Now regarding the ILS in the case of the AIRBUS it becomes a coupled approach what does that mean... Basically that it couples the Autopilot functions directly from the Glide and Localizer so the Flight Directors help you correct wind, and mantain proper track when making the ILS approach, so it helps you to fly it even better than from only following the Glide and Loc Diamond markers on the Bus... So try using the FD´s they are a great tool!

Regards,

Roberto

[ryanf]

Thanks Roberto. Thats good information.

So back to my original question - in PM, if I drift off the glideslope but then start to follow the FD needles and keep them centred, should they direct me to correctly reintercept the glideslope or will they cause me to repeatedly over-shoot and under-shoot the glideslope....at least this is what seems to be happening to me...if I am above the glidelsope, the horizontal bar will command pitch down, but only change from that commanded pitch as I cross the glideslope, which is too late...I miss it.

/Ryan.

[sas550]

Since I never flied a Boeing or airbus I can't say how the FD is reacting irl, but in the PM boeing suite the vertical bar is very slow to compensate for speed/pitch control. Flying with the vertical bar as guide gives me very poor speed control. After a while you learn how it 's going to react so you can be ahead of the director. I guess that's not how it's supposed to be.

[Brian]

Hello,
the flight director (FD) displays guidance commands from the Flight Management and guidance Computer (Airbus:FMGC), (Boeing:FMS) on the Primary Flight Display (PFD).
You may fly the aircraft manually, following FMGC or FMS guidance commands or crosscheck the FMGC, FMS orders when the autopilot is engaged.
The FD pitch and roll (cross, or v-bars) show pitch and roll demands generated by the respective Flight Management unit to keep the aircraft on a selected flightpath.
The pitch channel is displayed if a vertical mode (ALT HOLD,V/S, V-NAV,LCNG or GS) is engaged.
The roll channel is displayed if a lateral mode (HDG,L-NAV or LOC) is engaged.
During manual approach the use of the FD is strictly recommended to keep the aircraft within limits.
Brian

[Trevor Hale]

Hey Ryan, sorry I took so long to respond. I think what we have learned here is that you should be able to follow the FD all the way down, and is actually recommended. As we have learned the fd is a little slow to respond in PM. So here is what I offer. Sometime over the next couple days (Sooner if the Wife doesn't come up with any more chores for me) I will attempt to see how my FD behaves flying the ILS.

I will keep you posted.

Best regards, Trev

[Michael Carter]

The problem I have with the FD is mostly during cruise when making a course change. The bat wings will be hauled all the way to the left or right after selecting a new frequency or heading on the HSI.

I know which way I have to turn and how much intercept angle to use. I don't know about the newer Boeings and Airbus FD's but the Sperry FD109 is not very worthwhile during cruise.

After setting up for cruise, with the aircraft 'on step' you have to manually turn a knob on the FD panel to set the bat wings where your cruise attitude is. Well, I already know what that attitude is, why do I need a device to tell what that attitude is that I have to set to begin with?

That attitude will also change over time with fuel burn-off, so then you get to adjust it again for a setting you already are aware of.

?????

For a missed approach or a go-around it does help out though. After the Go-Around paddles are punched on the throttle, the FD is commanded to the pitch attitude needed for climb out. This is the only instance in the 727 where it is extremely useful, and it's the only time that it's automatic.

[ryanf]

Hi All,

was speaking with an Aer Lingus A320 pilot this evening and he told me that when he instructs pilots on the 320, he tells them that there is a little lag in the FD on approach, so really to watch the VS - should be about 800 fpm in a 3 degree glideslope, so as glideslope is being intercepted, adjust pitch to get that descent.

Following FD exactly can cause successive under and overshoots - as well as A/T trying to compensate for varying vertical speeds and adding to the overall approach destabilisation.

cheers,
Ryan.

[dodiano]

Yupe that is true sometimes there is a little lag but that is mostly due to the Quality of the ILS beam specially on the Glide Slope cause I have flown Full ILS and no lag on the FD´s... But I have never seen an overshoot with the ILS buddy sorry about that but is not true the FD´s specially on the Glass Cockpit planes are the only way you fly and they are trully precise.

Regards,

Roberto

[ryanf]

Hi Roberto,

thanks for the info.

I might not have explained it properly - how I understood it was that if you have an FD lag, then its easier to over-compensate and thus destabilise so its good to anticipate the glideslope a little also and not always blindly fly with the FD needles centred.

I appreciate your expert advice :)

thanks,
Ryan.