View Full Version : Flight director disagree

tubby linton
27th Jul 2007, 23:19
I recently saw the FDs of my old Airbus go into totally different modes(ALT*,GS*).I have never seen this before on a bus and there is no warning to tell you it is happening!!Has anybody else seen this on an old bus?

28th Jul 2007, 01:17
No warning?
Hard to believe, but perhaps true.
Now, this happens occasionally on the L1011, but it is clearly noticeable, via the autopilot/flight director mode annunciators.

What you see is what you get, and if it ain't right, recycle mode selections.

Surely Airbus has some similar procedure....:}:rolleyes:

28th Jul 2007, 08:09
Had it happen in the 320 (sim) the other day.

The FMGC's had dropped to independent mode for some reason.
One went left one went right, quickly changed the AP's over to the side going the correct direction and kept a good eye on it.

In the end was told to pull the cb and reset the fmgc, did the trick and sorted it out.

Don't know if this was just a sim bug or happens in the same way on the a/c.

28th Jul 2007, 18:04
Don't forget that the FD is only a guidance system and that you should look "through" it, not follow it if it's not giving you what you want. My experience with the airbus is that a reset usually works.

Willit Run
28th Jul 2007, 21:50
I've seen it happen on the A-300, the L-1011 and the 747. You do have to use it as a guide, always keep the raw data in the scan as well!

31st Jul 2007, 07:09

Saw a similar thing on one of our shiny new 319's the other day, during the climb out their was a difference in the pitch display between the left and right F/Ds, of at least 3 degrees (reasonably significant at FL360). I have been told that if the other A/P was engaged it would have chased the demand in the pitch of it associated F/D, which might not have been that comfy for the punters.

Is this because each FMGC is working out its own target climb speed, or is the airbus just strange???


31st Jul 2007, 07:58
Depending of FMS you have, when on grd go to REF, select A/C sensor status, next, and it will show you any system malfunction of last sectors (up to 6 I guess), maybe. ;)


1st Aug 2007, 19:35
......it happened again today!
Where is that ref page that you mentioned? i couldn't find it, is it a part of the atsu/aids page?
Could you give me another clue...

1st Aug 2007, 19:49
It's funny, cause I have some difficulties to find out which FMS we have installed, but I think it's Honeywell.

It has a button REF....

and so on.

BTW, you can use it inflight as well.

3rd Aug 2007, 14:04
I've seen it happen on the A-300, the L-1011 and the 747. You do have to use it as a guide, always keep the raw data in the scan as well!

Easier said than done. Let's face it - your eyes are glued to the FD needles on an ILS and the only way to scan raw data info while locked to the FD, is to have the standby ADI ILS in view during the approach. As far as "looking behind" a FD display at the little aeroplane it hides so successfully, -well that is well nigh impossible less you lose concentration on the FD needles.

You have only to see how poorly some pilots fly raw data non-automatics to see they have been locked on to the comfort of FD's for most of their current flying experience. Meaning they were unable to keep the raw data in the scan.

tubby linton
11th Aug 2007, 22:20
Sorry for the late reply.The aircraft was set up for an auto land with both ap engaged.GS* was shown on the FO pfd,and ALT* on CPT pfd.Due to the autoland condition AP1 is master so it follows FD1 guidance.FO FD pitch bar shows an increasing pitch down demand.No warnings were triggered by any aircraft system.I ended up throwing it all away and flying a visual approach.
FD1 never captured the GS and remained armed.I was just glad we were not having to do this for a real autoland!

Clarence Oveur
16th Aug 2007, 09:30
There is good reason for the recommended procedure of not engaging the 2nd AP/FD untill after GS capture.

tubby linton
16th Aug 2007, 16:47
The aircraft was in GS* but only one one side!!From memory on the 320 you could get gs in white rather in blue with certain failures.This would mean that it was armed but would not capture!In this case such a subtle failure may have been missed.

17th Aug 2007, 02:35
Centaurus, your eyes should not be locked on to the flight director bars. Yes you should have them in your scan but you really should be watching the instrument behind them to monitor raw data, not the standby instruments.