GoogleBoy
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What's New With Air Transat Rudder Separation?

Sat Apr 16, 2005 6:30 am

Any updates anyone on this event?
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bennett123
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RE: What's New With Air Transat Rudder Separation?

Wed Apr 27, 2005 8:24 am

 
GoogleBoy
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RE: What's New With Air Transat Rudder Separation?

Mon May 02, 2005 10:59 pm

Quoting Bennett123 (Reply 1):
Try FAA AD 2005-07-07.

Thanks for your insight Bennett123.

I read the AD. I am quite puzzled. Here is why.

1. The French Airworthiness Authorities (the DGAC) do not specify in their directive the reference SRM (Structural Repair Manual) pages to check for damage limits on rudder hinges and dents in the composite sandwich panels. This means that the inspector does not have the baseline limits to compare with his observations of damages on the hinges. How is he going to determine if he should report the damage to the OEM (Airbus)?

2. They call for a general visual inspection. They do not request an NDT inspection at the hinges. They should because if there is a crack it is likely it will not be visible since it could be at the pin-bushing interface or at the bushing-lug inner face interface. So, you could still have after inspection aircraft flying with cracked attachements.

3. The AD calls for visual inspection for damage that are oubvious. That is a dangerous understatement. The purpose of an NDT inspection (i.e. Eddy Current) is to detect damages that are not obvious to the naked eye. Aren't we taking sort of a gamble with this type of insufficient inspection?

Your thoughts.

Now imagine if the same issue would happen to the elevator hinges. Deep dodo folks...
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VC-10
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RE: What's New With Air Transat Rudder Separation?

Mon May 02, 2005 11:13 pm

Quoting GoogleBoy (Reply 2):
The French Airworthiness Authorities (the DGAC) do not specify in their directive the reference SRM (Structural Repair Manual) pages to check for damage limits on rudder hinges and dents in the composite sandwich panels. This means that the inspector does not have the baseline limits to compare with his observations of damages on the hinges. How is he going to determine if he should report the damage to the OEM (Airbus)?

You inspect for damage, if you find any, you refer to the SRM. If it is within SRM limits all well and good. If it is outside limits you inform your structures department who may contact AI if it is outside their experience or if there is a requirement to.
 
GoogleBoy
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RE: What's New With Air Transat Rudder Separation?

Mon May 02, 2005 11:28 pm

Quoting VC-10 (Reply 3):
You inspect for damage, if you find any, you refer to the SRM. If it is within SRM limits all well and good. If it is outside limits you inform your structures department who may contact AI if it is outside their experience or if there is a requirement to.

Yes VC-10, perfectly correct; but the point here is that the DGAC did not refer to the appropriate Section of the SRM to check observations against the damage limits of the manual. Isn't odd, wouldn't you convene?
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NAV20
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RE: What's New With Air Transat Rudder Separation?

Mon May 02, 2005 11:56 pm

I must confess to a lingering sense of doubt about this business. Obviously the programme of extra inspections is a sensible precautionary step. But it looks as if the authorities have already decided that what happened was the result of some sort of 'material fatigue'.

The Air Transat aeroplane was flying at 35,000 feet on autopilot. The rudder was not in use at all, except to the extent that the 'yaw damper' was engaged. I believe that yaw dampers only move the rudder fractionally - perhaps a degree or two, no more.

If a rudder was suffering from 'fatigue' you would expect it to fail eventually. But common sense says that the failure would most likely occur at a moment when the rudder was subjected to a fair amount of strain - not in normal flight, with the autopilot engaged.

If anyone hasn't yet seen pictures of what was left of the Air Transat rudder after the incident, there are some on here. I don't readily see how a tiny deflection by the yaw damper could have caused such massive damage. I certainly hope that the authorities are considering other possibilities besides mere 'fatigue'.

http://coppermine.luchtzak.be/thumbnails.php?album=338
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
GoogleBoy
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RE: What's New With Air Transat Rudder Separation?

Tue May 03, 2005 3:27 am

Quoting NAV20 (Reply 5):
If a rudder was suffering from 'fatigue' you would expect it to fail eventually. But common sense says that the failure would most likely occur at a moment when the rudder was subjected to a fair amount of strain - not in normal flight, with the autopilot engaged.

Fatigue failure is incidious in nature. What matters in the cycling of the load more than its magnitude.

Typically, on a transport aircraft, gust occurrences are the culprit in aircraft fatigue of structurally significant components. Critical parts are usually designed to cater for the critical flight load with this gust effect superimposed on it.

However, when a part has reached a certain number of cyclic loads (some of high magnitude such as in a mild or severe strom) cracks start to initiate in the metallic structure and propagate a little further with additional cycles. Once the crack has reached a critical size, all it takes for failure is the next cycle load even if it is of low magnitude. So in a nutshell, when the part has a crack that has grown steadily in-service to critical size all you need is the next cycle irrespective of the magnitude of the load.

Mind you on the A310 you may have also the coupling of the aft end fuselage vibrations in-flight with the vibration of the tail. I noticed when flying on those a/c that the aft end fuselage is not as stiff as on Boeing airraft. You would notice it if you stood up in the aft galley and noticed the number of amplitudes it takes for the aft end to return in neutral position once a lateral gust has 'hit' the aircraft. We called that aeroelasticity effects inducing coupling modes of vibration between the fuselage and the tail. Now, picture this: You get induced fuselage vibrations from the aft end of the fuselage and you couple that vibration with that of the huge tail. Guess what? What do you think the upper hinge in the rudder sees when this coupling happens. Hell of a cyclic loading is the probable answer. It could be therefore that when the engineers design and tested the rudder hinge attachments they did not cater for this type of real-life coupling mode. This could have been prevented if they did not go too aggressively on weight reduction during the design of the aircraft fuselage frames, stringer, and skins. Typically, when the program director must seek weight reduction, these parts are given a trim to get more weight out. The skins are usually a first candidate since at least 25% of the weight of a fuselage is in the Skins. So they manufacture deeper skin pockets wit the resulting effect that the fuselage is not as stiff as it ought to be to alleviate risks of coupling mode vibration in the tail.

Hope this help. I had an initial thread on the Air Transat rudder departure where I wrote extensively on this subject.

Cheers mate.
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bennett123
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RE: What's New With Air Transat Rudder Separation?

Tue May 03, 2005 3:37 am

I get the impression that Airbus are not looking for something specific, but basicly saying "Is there anything wrong with the tail of your A300-600/A310".

I think that if they knew or suspected a particular component then the AD would be more specific. If these checks turn up something then there may be another AD.
 
GoogleBoy
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RE: What's New With Air Transat Rudder Separation?

Tue May 03, 2005 3:48 am

Quoting Bennett123 (Reply 7):
I think that if they knew or suspected a particular component then the AD would be more specific. If these checks turn up something then there may be another AD.

Yep, seems like the approach they're using. However, if the check do not turn out anything else specific (from visual) and there is another incident (or accident) then I agree that there may be another AD.

Bottom line: in my opinion, this story deserves to be followed closely for other potential development. Let's hope no lives will be lost.
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bennett123
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RE: What's New With Air Transat Rudder Separation?

Tue May 03, 2005 3:54 am

I think that we would all be a lot happier when they find the cause.

The initial AD sounds like a fishing trip.
 
GoogleBoy
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RE: What's New With Air Transat Rudder Separation?

Tue May 03, 2005 3:59 am

Quoting Bennett123 (Reply 9):

I sent a query to the Canadian Transport Safety Board (TSB) tasked with the investigation and proposed a path for investigation.

I am still waiting for an official response (unlikely) :,)
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VC-10
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RE: What's New With Air Transat Rudder Separation?

Tue May 03, 2005 6:50 am

Quoting GoogleBoy (Reply 4):
but the point here is that the DGAC did not refer to the appropriate Section of the SRM to check observations against the damage limits of the manual. Isn't odd, wouldn't you convene?

No I wouldn't say so. As a professional Licenced Aircraft Engineer I can navigate myself around the SRM.
 
NAV20
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RE: What's New With Air Transat Rudder Separation?

Tue May 03, 2005 10:43 pm

Quoting GoogleBoy (Reply 6):
Now, picture this: You get induced fuselage vibrations from the aft end of the fuselage and you couple that vibration with that of the huge tail. Guess what?

Got a feeling - not a pleasant one - that you're on to something there, GoogleBoy.

To add to your points - if you're trying to save weight on an aircraft design, presumably you are pretty well bound to give early consideration to the tail - given that it's the part furthest from the CG?
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
GoogleBoy
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RE: What's New With Air Transat Rudder Separation?

Tue May 03, 2005 10:52 pm

Quoting VC-10 (Reply 11):

I don't doubt it; but it is normally Standard Practice at least in the US and Canada for Certification Authorities to specify the SRM damage limits section.

Just for sake of effective communications to minimize the risk of errors.
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Avionics
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RE: What's New With Air Transat Rudder Separation?

Fri May 06, 2005 4:56 am

The National Transportation Safety Board continues to
assist the Transportation Safety Board of Canada as it
investigates an accident that occurred March 6, 2005, when
an Air Transat Airbus A310-308 (C-GPAT) lost most of its
rudder in-flight while en-route from Cuba to Quebec City,
Canada.

The NTSB has dispatched a team of investigators to
participate in the readout of the aircraft's flight
recorders and the development of aircraft performance
studies; to participate in the examination of the aircraft's
vertical stabilizer, remnants of the rudder, and rudder
actuators; and to work with the TSB's chief investigator in
developing the issues to be addressed in the investigation.

Canadian authorities issued an investigation update on
May 4 that can be accessed at www.tsb.gc.ca, under "What's
New."

Based on information released by the TSB, NTSB
investigators have noted significant differences between the
circumstances of the Air Transat accident and two previous
accidents investigated by the NTSB that also involved
structural damage to composite components on Airbus
aircraft.

On November 12, 2001, American Airlines flight 587, an
A300-605R (N14053), crashed shortly after takeoff from John
F. Kennedy International Airport in New York City, killing
all 260 persons aboard and 5 persons on the ground. The
NTSB found that the vertical stabilizer separated from the
aircraft in flight after experiencing aerodynamic loads
beyond the plane's design strength following the first
officer's unnecessary and excessive rudder pedal inputs. On
May 12, 1997, American Airlines flight 903, an A300-600
(N90070), experienced an in-flight loss of control near West
Palm Beach, Florida. The aircraft landed safely. During
the recovery of the aircraft, the significant rudder pedal
inputs led to aerodynamic loads that caused damage to the
vertical stabilizer. The damage was not discovered until an
ultrasonic examination of the stabilizer following the crash
of flight 587.

In both of those cases, significant rudder inputs by
pilots played a major role in producing the aerodynamic
loads on the vertical stabilizer. Preliminary indications
from the Air Transat event data show that the pilots were
not manipulating the rudder before the events leading up to
the loss of the rudder.

Furthermore, NTSB investigators note that in the
flight 903 accident the rudder remained attached to the
vertical fin and no significant damage was found on the
rudder after the event. In the case of the flight 587
accident, the data indicate that the rudder remained intact
and attached to the vertical fin until the fin separated
from the airplane.

The NTSB will continue to participate and assist the
TSB of Canada's investigation into the reason for the loss
of the Air Transat rudder, and will continue to compare data
from the earlier accidents to determine whether there are
any similarities between all three events (beyond the fact
that all three aircraft experienced damage to rear lugs of
the vertical stabilizer).

All media inquiries about the Air Transat
investigation should be directed to Mr. John Cottreau,
Public Affairs Advisor, Transportation Safety Board of
Canada, (819) 994-8053, John.Cottreau@tsb.gc.ca.

- 30 -

NTSB Media Contact: Ted Lopatkiewicz
(202) 314-6100
lopatt@ntsb.gov
 
GoogleBoy
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RE: What's New With Air Transat Rudder Separation?

Fri May 06, 2005 5:10 am

Thank you Avionics for the update.

Quoting Avionics (Reply 14):
(beyond the fact
that all three aircraft experienced damage to rear lugs of
the vertical stabilizer).

I believe that this is key to the Air Transat Rudder Separation. There was a fatigue crack in the upper lug and initial failure started there with cascade failure there on. My worry, is that the current inspection called in the FAA AD is for a VISUAL inspection only. It is very hard for an inspector to detect a crack in a lug/pin/bushing assembly only thru visual. You really need an NDT inspection to detect those cracks. Besides, I read above with stupefaction, that it was after an Eddy Current inspection that cracks were found on the previous incident. So, planes are now flying with complete assurance of the structural integrity of the rudder upper hinge.
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