A320 Airframe vibration

[AME1117]

Hello Gentlemen

How many of you have faced airframe vibration issues on A320 family airplanes?

Thanks for sharing in advance

Ame

[Dan Winterland]

Often, usually about five seconds after extending the landing lights.

[Bus Junkie]

On a few airframes (2 or 3 out of the 30+ I can recall) starts about FL180 ends FL260 when above 280 kias. Seems to be common parameters. One company got info from Airbus saying there was not enough damping of a particular elevator servo. The company I'm with now no longer has the problem on that airframe (don't know what was done if anything).

[condorbaaz]

heard once about some SEC problem as well.
Once attributed to frayed/ damaged deicing boots on the stab, as well
but dont go by me , i am just a pilot...

[goeasy]

Boots? On an A320? You really have lost the plot! :ugh:

[PJ2]

AME1117;

I experienced airframe vibration a number of times on older A320's. The vibrations were about 6 to 8Hz and could be felt on a larger cycle of about 1 minute - about 20 seconds of vibration, 40 seconds of calm, and repeated, sometimes quite strongly, in the cockpit and through the thrust lever quadrant. I kept records in my log book and got a particularly bad airplane one day - climbing through about 270, Mach 0.76 and increasing, when the vibrations began. I asked my F/O to go back to see if anyone felt it in the cabin. He was a very sharp guy and returned about ten minutes later and said to me, "you have to go to the back of the airplane and look out". I did. I watched, as both horizontal stabilizers began fluttering up and down describing an arc of about 1 ft or so. They were fluttering at about 6 to 8Hz for about 20 seconds gradually damping then beginning again after about 40 seconds. The pattern did not vary with Mach or altitude. It would gradually stop after some time in cruise.

We'd been writing up airframe vibration for years. It was always dismissed as "gear doors", "flaps", "turbulence" etc.

I grounded our aircraft at the next station. I learned later that it was a known issue by Airbus and that another large US carrier had had experience and it was even written up in Airbus' larger "industry issues" publications they used to distribute. Why our maintenance people or flight ops people had so much trouble finding out what it was, was a mystery. The fix was as stated here - replace worn elevator bushings, and, using a special tool, bias the elevators "down" by half a degree (if I recall). The fleet problem disappeared overnight.

That's one experience. Hope it helps solve what you're looking for.

[king surf]

It happens on a few of our old A320's,and i find a gentle squeeze on the left rudder gets rid of the vibration.

[Ndicho Moja]

Many years ago the high frequency vibrations were attributed to some of the rubber seals between wing fillet/centre section and fuselage. More recently, vibration (moderate frequency) and felt through the floor in the cockpit, occurring between FL180-230 and speeds 280kts-310kts, can be attributed to excessive wearing on the TPFE (Teflon) bearings in the aileron hinges and even the hinges on the elevators and rudder.

Good luck.

N.M.

[IFixPlanes]

... We'd been writing up airframe vibration for years. It was always dismissed as "gear doors", "flaps", "turbulence" etc. ...

... Why our maintenance people or flight ops people had so much trouble finding out what it was, was a mystery. ...

Did you ever give the maintenance more hints than speed and affected area?
Worn elevator bushings are not the only cause of vibration.
Our crews have a reporting sheet (out of the AMM) that we please them to fill out:
http://img44.imageshack.us/img44/6329/vibrationreportingsheet.th.jpg (http://img44.imageshack.us/my.php?image=vibrationreportingsheet.jpg)


The hydraulic actuation to 0.5 degrees nose-up should be already done on A320Fam.
Ref.:
EASA AD 2007-0136
LTA 2002-514
CN 2002-514
SB A320-27-1114

[Airbusslave]

hi everyone,
A bit of new info on A320-200. a collegue of mine was flying back from JKT n he experience the same problem .
A/c was CRZ bout FL300-370.There was severe vibration at the rear part of the aircart. Auto rudder trim is normally bout +- less than 1degree. b'coz of the vibration, auto pilot was not able to control rudder input. the trim just went to 8degrees indicated on rudder trim window of the centre pedestial. they had to fly the aircraft manually all the way back. b'coz of the rudder trim at 8degrees, AP could not be engaged. that's something new.
:hmm:

[Joetom]

http://www.airbus.com/store/mm_repository/pdf/att00004406/FAST_SPECIAL_A320_ATA27.pdf
.
Though I read about single system checks can sort many of these problems, find the surface that like different positions with different hyds on and Bobs your uncle, thought rudder was top of the list.

[Dream Land]

Have occasionally had some vibrations, I feel the most important aspect of writing up the defect would be to use the Airbus form as previously posted by IFixPlanes, this form helps engineers pinpoint the problem and becomes part of the permanent aircraft history.

Cheers, D.L.

[Jimmy Hoffa Rocks]

by Sonia Bouchardie, Engineer Flight Control Systems, Customer Services, Airbus Industrie

Folloowing reports of in-flight vibrations on the A320 Family, an intensive flight test

campaign was launched by Airbus Industrie to determine the different sources of elevator

vibrations. They are described in the Trouble Shooting Manual (TSM) Chapter 05-50-00,
and each possible cause is associated with corresponding trouble shooting procedures.
The TSM also provides a recording sheet to help operators establish the cause of vibration.
The main source is the elevator system, which accounts for more than 70% of all
vibrations. Further to the flight test campaign, it was revealed that the phenomenon was in
fact a Limit Cycle Oscillation (LCO) which is a sustained vibration at a fixed frequency
with limited amplitude and having no impact on flight safety.
This article describes how to avoid elevator vibration through the incorporation of a
modification on the spherical bearing of the elevator servo control and a new elevator
Two solutions were developed to eliminate these two causes: reduce backlash and
increase hinge moment.
CONCLUSION
The extensive work performed by the Airframe Vibration Task Force led to conclusions for eliminating airframe vibration
which have since been proven in service. The effectiveness of these modifications has been clearly demonstrated through
the positive feedback from the Operators. Therefore as a preventive measure, the incorporation of the Service Bulletins are
highly recommended by Airbus Industrie.





(

TO REDUCE BACKLASH

Several cases of excessive play within the spherical
bearings of the elevator servo control, due to premature wear
of the Teflon liners, were discovered during inspections
following reports of in flight airframe vibrations.
This condition has now been eliminated thanks to higher
performance NMB bearings, introduced on the elevator
servo-controls through the LUCAS Service Bulletin 31075-
27-17 and Airbus Service Bulletin A320-27-1111. This
modification incorporates an additive in the existing liner,
and chromium and super finishing of the inner ball to reduce
the wear rate and friction coefficient. Also the maximum
acceptable value for backlash, measured at the elevator
trailing edge has been reduced from 10mm to 7mm, as
described in the AMM.
TO INCREASE HINGE MOMENT
The Airbus Service Bulletin A320-27-1114 describes the resetting of the
elevator neutral position to 0.5 degree (aircraft) nose up. Accomplishment of
this modification ensures that the elevators are aerodynamically loaded in an
appropriate manner in order to eliminate vibration, even during flight in
turbulent conditions.
Those changes have no effect on aircraft performance and there is no
change in the handling characteristics of the aircraft, nor is there any penalty
in fuel consumption. This modification has been developed to fit easily into the maintenance program.
To perform the revised elevator rigging, a new elevator rigging tool,
developed by Airbus Industrie, enables the new neutral position to be
determined. It is highly recommended that this new tool be used, as it allows
more accurate rigging through a simplified procedure. Nevertheless, the
elevators can also be set using the previous tool which was developed
originally to set the elevators to a 0 degree position.
Therefore the Aircraft Maintenance Manual (AMM) procedure now
describes how to set the elevators to the 0.5 degree using the original tool orthe new tool.



ADVANTAGES


As a preventive measure, these modifications will:





improve the fleet reliability due to the new elevator servo spherical bearings and revised elevator rigging,


improve passenger and crew comfort by removing the causes of vibration,
reduce maintenance costs."

[PJ2]

IFixPlanes;
Did you ever give the maintenance more hints than speed and affected area?
Yes we did. We recorded most of the details seen on the sheet you provided, (thanks) but that sheet didn't exist when we were experiencing these vibrations - this was between 1994 - 1996. We'd been writing such snags for a few years and it was discussed informally with other crews but when I flew the fins and checked the responses the snags usually came back with comments about checking gear doors, flaps and other such items. As well, it was only on about three fins that I recall. Frankly I never had the impression from the snag responses I read that they had checked with Airbus or if they did maybe who they checked with didn't know. The problem was outlined in the publication I mentioned that I discovered some time later but which was current at the time, specifically referencing a large American carrier's 320's and their solutions, so someone at Airbus knew, but I never saw anything anything about flight control vibrations, (asking for comments, taking a look, etc). We looked at the ECAM each time but I recall the elevator indicator was steady during the event in question. This was 6-8Hz however - fairly fast - I'm not sure how sensitive the flight control indicators are but at M0.77 I don't think the tiny movements of the elevators that would be all that was needed, are going to show up on the ECAM. The vibrations were solid and felt throughout the aircraft - front to back and this too, was reported. We did try a few control inputs to dampen the pattern but no joy. Before the subject flight, no one had thought to go back and actually have a look at the stabilizer, partly because we didnt' expect flutter to be a problem and I suspect our maintenance guys felt the same way. I think we were all quite surprised (to put it mildly) at what we saw and wrote up.

Today it's obviously well known and well understood - I don't think it was back then.

[robertbartsch]

Is this related to the VS problems that I have been reading about lately?

[subsonic69]

yup same form.. and our planes are averaging 4-5 years old so its not only on the old A320s

if i remember correctly ours have a prob with the rudder too..