Flight Director versus ILS Indicator

[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.