A-320 Vibration Bearing in Stab. or Elev

[Mach trim]

Could someone give some more info on a similar 320 case

320 Captain does flight with aricraft vibration. Then vibration gets worse, on landing aircraft is grounded.

Sent to maintenance specialists bearings found completely worn and need of replacing in stablizer or elevator

This is not an old new A-320 but relatively new.

Another separate A320 gets light-moderate vibration in descent at around 310 knots at FL 170. Vibration seemed to occur for about 10 seconds. An and climb and that speed and FL.

A veteran Captain mentions that this has happened years ago.


How about the bulletin OEB system of Airbus or bulletins

Anyone know of any bulletins or OEB's on this, if not Why arent there any ?

I have my doubts about Airbus's OEB and bulletin system where stuff gets deleted.

Any thoughts ?

[Wodrick]

There is a vast SIL about airframe vibration which ends with a vibration reporting proforma. Using the proforma your clever people in engineering are able to isolate the problem, usually quite quickly. In the company I worked for there was a copy or two on the flight deck, usually in the documents folder. Being retired now I can't give you the SIL number but your engineers should be aware of it and be able to supply a copy of the fault finding proforma. Not much of an engineering department if they can't !

[Mach trim]

Thanks ASFK and Woodrick.

Would like to get the SIL number and will ask maint for more info.

How serious is this if these bearings get too worn and break ? What happens then to the stab or elevator ?

Vibration report in the document folder, we dont have them but should have them in our documents folder



An airplane of ours had been flying for some time with this occasional vibration. Not enough info to us pilots me thinks on this.

Jammed stab is not very nice.

[Wodrick]

ASFKAP Electronic Tech Log !
and then there is the nose u/c doors, wing body fairing, pack inlet / outlet doors to name a few ...............

[Diesel8]

Like someone else said, it is simply due to worn eyelets/bushings. It will not cause a stuck stab.

A long time ago, I heard it was was caused by a vibrating elevator, due to the stabilizer trim providing no load on elevator, hence if there is any freedoom in the setup, it can vibrate a bit.

I thought Airbus had changed the setup, a changing the stabilizer setting to provide a bit of load on the elevator, but perhaps not, since I had the same problem a couple of months ago.

Under all circumstances, it is a known problem, but doesn't seem to be something to be overly concerned about, although it is annoying.

[Mach trim]

" Under all circumstances, it is a known problem, but doesn't seem to be something to be overly concerned about, although it is annoying."

Diesel, thanks for that.

Curious

If it is a known problem then why no operational info from Airbus on it ?

Anyone got a link to SIL's on it ?

My question is if its not anything to be concerned about then why did experienced maintenance people ground the aircraft ?

Curious then diesel you do write such vibrations in the tech log then ?

When bearings get worn they need to be changed in this case the aircraft had come back from a C check a month ago.
Evidently this was not done ?

I had the vibration and was surprised the grounded the a/c. As the vibration had been reported before.

Flying around with a vibration and it is ok for me doesnt cut it
with a relatively new airplane, give me a Boeing.

[Diesel8]

MachTrim,

I did not say it shouldn't be written up, nor did I say, that it isn't cause for investigation.

As for grounding the a/c, quite rightly so until the cause has been determined and rectified.

Now having said that, I first heard about the problem with bearings/bushings/eylets about 8-10 years ago, and I am simply relaying what I was told. It might not be correct, but have never heard any other story.

I know the mechanics I have spoken to wrt, this issue, seem to always suspect the elevator, that is after they have made sure that there were no open access panels, weatherstrips etc.

Just found the "dirt" from Airbus:

http://www.content.airbusworld.com/SITES/Customer_services/html/acrobat/fast_23_p10_11.pdf

Here is a rather longwinded FAA Airworthiness Directive (AD) on the same issue:

FR Doc 05-21427 (http://edocket.access.gpo.gov/2005/05-21427.htm)

As to Airbus having fixed the problem, I am not sure, the a/c I had a problem with was less than two years old.

Further, it had just come back from a check, the vibration was written up on the return flight from said check, the a/c was inspected and the problem reoocurred on a flight (mine)shortly thereafter.

P.S. Enjoy the Boeing, no tail problems there:}

[winglit]

I can recall the exact same thing happening to an A320 straight out of C check from GAMCO.

It was an empty ferry flight with just 2 pilots, 2 engineers and a storeman on board.

We had to lock out a pack due to a faulty pack valve, so we were flying at a limit of 31,000ft as per MEL restrictions. After T/O out of Abu Dhabi we were flying along the coast of the Gulf. By the time we got about as far as Bahrain, the A/C started to vibrate badly. I was standing in the rear galley at the time and was convinced that something had fallen off. Something like an elevator servo access panel. The vibration was similar in sound and feel to a pneumatic hammer drill, and all in the vertical axis. I went to the flight deck to find both pilots bouncing in their seats unable to read their instruments due to severe vibration.

A scary time to say the least. My other engineer colleague joined us in the cockpit where we discussed the best plan of action. All credit due to the captain who used all his resources to help him with his CRM. He was in favour of trying to isolate the fault by trying different configs (SECs /ELACs / FACs) etc. We advised that it probably wasn't wise and the priority was to get the A/C back on the ground as gently as possible. He agreed with us and we declared a MAYDAY. ATC gave us a gentle 180 turn and we lined up on a long approach on the opposite runway into Abu Dhabi. As we slowed down for approach, the vibration stopped and we made an uneventful landing.

After days back in the hangar we couldn't find anything wrong with the A/C. We had dug out all the SILs and TFUs from Airbus and couldn't find anything relevant. We eventually called Airbus Tolouse who told us to replace all the hinge line bearings in both the rudder and the elevators. Even though backlash checks were well within limits. We also replaced all elevator and rudder servos. The backlash checks on the stab were also well within limits so we didn't replace it.

As we hadn't found anything really conclusive we decided to take the A/C up for a flight test. I was the engineer on board. We managed to reproduce the vibration again. Exactly the same as before. Then we started playing with the EFCS. At one point the captain who was our resident test pilot was flying it in Direct Law with everything switched off! We managed to ascertain that the vibration was purely a function of IAS. You could accelerate through the vibration and fly a MACH no and the vibration went.

Back to the drawing board and the head scratching prevailed. Airbus then told us to replace the stab jack. Even though all checks were in limits. In fairness to them, it did fix the vibration on the next flight. Our questions remained why these wear limits existed in the MM if they were not suitable for safe flight. We never got an answer, but I believe that the backlash limits on the hinge line bearings and the stab have now been reduced significantly.

My own theory however, is that there was not enough aerodynamic loading on the stab and the slightest play would cause oscillation which is amplified though the airframe. I reckon you would be able to reproduce the same vibration on many A320s if you flew at low level(sub FL30), high IAS (not MACH) and empty.

Any 320 jocks fancy trying it?

[Mach trim]

Thank you Diesel for the link and info
thats what I was looking for will pass it to our safety people

sorry for misunderstanding

Thanks winglet

Seems Airbus is keeping this quiet.

[Diesel8]

MachTrim, NP, happy to help.

As for keeping it quiet, the FAST article has a 1998 date, so it has been known for a while.

In general though, I think Boeing is better at sharing information with all operators, but nonetheless I am a fan of Fifi.