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Marcel_MPH
25th May 2004, 12:43
Hi all,
I have a question regarding the following incident a few years ago. A Lufthansa A320 went for some technical complaints into a general check. During this check the controll surfaces connections were all being looked after by deconnect them and reinstall them. During the reinstallation of the wires, left and right were not correctly installed making the aircraft bank right when a left bank was initiated by the pilot and the other way around. This was noticed by the PF (captain) during take-off when he tried to correct a slight right bank due to some crosswind. This made the aircraft bank even further to right while the wing almost made contact with the ground. The PNF (co-pilot) anticepating quickly, took over controll and made a safe landing.

I guess before every flight (during taxi most of the time) all control surfaces are checked by moving the controll units (on both sides) and verify these movements on the lower ECAM. I wonder how this ECAM is connected in relation with the "controll unit" and the controll surfaces. Does the lower ECAM display the movement of the surfaces like they are moving (so any irregularity can be observed before it becomes a serious incident) or does it show the "side-stick" movement initiated by the pilot himself?

Thanks in advance,

Marcel_MPH

-<M4v3r1ck>-
25th May 2004, 14:03
I think that incident was discussed fairly recently on pprune. Run a search...think it was in the Tech forum as well...

Mav :ok:

FlapsOne
25th May 2004, 14:04
I was told in TLS (recently) that the Lower ECAM displays what's actually happening at the control surfaces so, theoretically, if the control checks are done correctly, that same problem should not happen again.

If you watch the lower ecam in flight there are plenty of minor control deflections indicated without any side stick input.

Lu Zuckerman
25th May 2004, 14:32
I can only speak to the A-310 but I can assume based on that experience the same condition might exist on other Airbus aircraft. On the A-310 Command sensor unit there are two Cannon type connectors which can be interchanged. The only guard against misconnection is a small sticker on the connector and the connection that I believe says A or B. If these stickers come off the technicians can misconnect them. There is no outward manifestation of a problem but if the technician has to troubleshoot the system he will be driven crazy because he canít find the problem.

The PPUs have the same problem in that the connectors are not keyed and can easily be interchanged. If this happens the computer will sense this and lock the system up.*** The wing tip brakes have the same problem as the CSU in that the connectors can be interchanged and troubleshooting will again drive the technician crazy.

The PCU solenoid connectors can also be interchanged and the only guard against that is the cables are tied back and the connectors are not keyed. If the tiebacks are cut for maintenance there is a possibility of misconnecting the connectors.

It is a part of any design specification that requires that connectors be keyed so that there is no possibility of misconnection. The manufacturer did not want to do this because of costs and a perceived schedule impact.

*** Thatís if the computer is capable of diagnosing the problem but thatís another story.


:E :E

Marcel_MPH
25th May 2004, 17:10
That's the same thing I was thinking Lu. Since both connectors can be interchanged the chance of a misconnection between the "side-stick" and the controll surface is fairly greater than when both are marked. The incident happened a few years ago so I suppose Airbus did a recommendation to all the airlines already operating the aircraft and took some action to prevent this kind of mishaps in the future.

I found this site which explains the principles of "fly-by-wire".

Airbus "fly-by-wire" (http://www.airbus.com/pdf/customer/fast20/p2to9.pdf )

Marcel_MPH

wrenchbender
26th May 2004, 00:14
Marcel; The incident you are referring to was caused by the fact that the technicians had to replace the electrical connector that the ELAC computer mates with in the electronics rack. When installing the wires in the new connector, several got crossed, causing the captains stick to command a left vs a right roll, and vice versa.

The flight control surface position indications on ECAM are directly displayed from position transmitters on the surface itself, not from whatever is being commanded by the stick.

Marcel_MPH
26th May 2004, 07:31
So if the pilots monitored the ECAM closely before flight they could have seen the problem and take appropriate action....

Marcel_MPH :cool:

FlapsOne
26th May 2004, 09:24
Thinking about this logically (cos I haven't got an engineering brain) wrenchbender must be right.

The sensors will pick up surface movement, irrespective of stick deflection, and will 'lock out' mis-behaving items (plus their opposite number).

The way we currently do the flt ctl check pre-flight HOPEFULLY would pick up any anomaly. We have ditched the routine order of UP DOWN LEFT RIGHT in favour of a random order so that there is less chance of 'reading a script' and more chance of 'saying what you see'.

Interesting topic.

Lemurian
26th May 2004, 11:04
Hello,
this is the link to the incident :
http://aviation-safety.net/database/2001/010320-0.htm.
After the incident,many operators have insisted on a proper x-check of trhe FC position.As Flapsone suggests,one pilot pushes controls to max deflection the other announces "full left/right..."

Marcel_MPH
26th May 2004, 12:27
Now I've read the investigation report I understand why the crew didn't pick up the malfunction since the "flight control check" wasn't included on the after start checklist at the time.

Luckily the PNF responded quickly and prevented another disaster.

Marcel_MPH :cool:

square leg
28th May 2004, 22:47
Back then I believe LH only checked what happened on the PFD during the F/CTL check, i.e. "+" up-down & left-right as opposed to watching the SD F/CTL page. That has changed.

Then, back then maintenance were only required to check one (1) sidestick after such a maintenance procedure. That has also changed since. Now both sidesticks are checked.

This just shows where the chain of events can start. Sometimes as far as the design of aircraft.

Safe flying:ok:

SimJock
30th May 2004, 19:27
I am very surprised that the ELAC's didn't generate an ELAC Fault of some description after this wiring mistake. They seem to complain readily about far less important problems and something like a stick being wired incorrectly should have promulgated a fault warning IMHO.