A-300 engines
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If they take a closer look at the fin fracture site, they may determine that there is evidence of pre-existing delamination due to water absorption into the composites layers (due poor/blocked drainage and ventilation around the interior base of the vertical fin). It may be that pools of water get trapped there around the fin periphery during flight through precipitation or during aircraft washing.
I would guess that the "max power" call may well have been related to the fin tearing cleanly away above the mounting bolts - and the sudden C of G change/pitch-down.
One could theorise that as the base of an internally water-soaked fin gradually became delaminated and lost its structural integrity (and rigidity), it may well have increasingly suffered from a low frequency (unnoticeable) vibrational flutter of a quite low amplitude - but sufficient to cause the composite fibres (in the mat) to "work" (and so weaken the surrounding area). Flight 587 may have been the flight upon which it lost that last critical bit of strength and quickly degenerated into a rapid L/R flutter mode prior to detachment. Composite fibres have always been a concern because external coatings can easily conceal substantial damage, normally from blunt object trauma. Because of the time in service, this may well be one of the first instances of moisture-induced composite "fatigue" that the aviation industry has experienced. I think I recall the chap who fixed my carbon-fibre airplane telling me that once that process of delamination starts, the fibres can suck up water like a wick and the delamination spreads like a cancer beneath the gel-coat.
It may all come down to insufficient inspection protocols (overconfidence), inasmuch as the industry has always applauded the fact that composites are not prone to fatigue cracking nor corrosion, as is metal. It sure as hell is prone to moisture absorption (and UV light) however - and that might well prove to be the case here.
With or without the "water rot" delamination, a composite vertical fin is subject to the long term high-frequency vibration of flight and it may be the case that this can have a "corrosive" effect upon the fibres of the composite mat, eventually leading to a stress fracture near to its attachment base. Once detached the rudder would have been undamped and flailing violently against its travel stops - so it's not surprising at all that it should in turn detach from the fin on the way down (i.e. hinge-fracture) while in its sycamore leaf mode.
The engines would have detached from their pylon mountings due to the lateral (centripetal) stresses (for which they are not designed) during the ensuing high g spiral dive.
I would guess that the "max power" call may well have been related to the fin tearing cleanly away above the mounting bolts - and the sudden C of G change/pitch-down.
One could theorise that as the base of an internally water-soaked fin gradually became delaminated and lost its structural integrity (and rigidity), it may well have increasingly suffered from a low frequency (unnoticeable) vibrational flutter of a quite low amplitude - but sufficient to cause the composite fibres (in the mat) to "work" (and so weaken the surrounding area). Flight 587 may have been the flight upon which it lost that last critical bit of strength and quickly degenerated into a rapid L/R flutter mode prior to detachment. Composite fibres have always been a concern because external coatings can easily conceal substantial damage, normally from blunt object trauma. Because of the time in service, this may well be one of the first instances of moisture-induced composite "fatigue" that the aviation industry has experienced. I think I recall the chap who fixed my carbon-fibre airplane telling me that once that process of delamination starts, the fibres can suck up water like a wick and the delamination spreads like a cancer beneath the gel-coat.
It may all come down to insufficient inspection protocols (overconfidence), inasmuch as the industry has always applauded the fact that composites are not prone to fatigue cracking nor corrosion, as is metal. It sure as hell is prone to moisture absorption (and UV light) however - and that might well prove to be the case here.
With or without the "water rot" delamination, a composite vertical fin is subject to the long term high-frequency vibration of flight and it may be the case that this can have a "corrosive" effect upon the fibres of the composite mat, eventually leading to a stress fracture near to its attachment base. Once detached the rudder would have been undamped and flailing violently against its travel stops - so it's not surprising at all that it should in turn detach from the fin on the way down (i.e. hinge-fracture) while in its sycamore leaf mode.
The engines would have detached from their pylon mountings due to the lateral (centripetal) stresses (for which they are not designed) during the ensuing high g spiral dive.
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Belgique;
Your post is one of the best I have seen
for technical content & I believe that you
may well have pin pointed a problem,
I have long been suspicious of composites as
damage can remain undetected.
such a tragic incident, very very sad :-(
Your post is one of the best I have seen
for technical content & I believe that you
may well have pin pointed a problem,
I have long been suspicious of composites as
damage can remain undetected.
such a tragic incident, very very sad :-(
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I Agree with Belgique
So what would happen when the A/c is crusing at 37000 feet at -60 What happens to the already soaked composite structure then??.
A known problem to Airbus methinks.
[ 16 November 2001: Message edited by: 100LL ]
once that process of delamination starts, the fibres can suck up water like a wick and the delamination spreads like a cancer beneath the gel-coat.
A known problem to Airbus methinks.
[ 16 November 2001: Message edited by: 100LL ]
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Incidentally GRP pressure pipes have been shown to fail in exactly the same manner, except it is the hydraulic pressure that damages the matrix as it creeps along the fibres once they are exposed, rather than freezing of the water.
No, I don't work in the aviation industry!
No, I don't work in the aviation industry!
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Carbon composites are frequently used on submarines, so composites and water can live together quite happily without the composite failing. Depends what they are built for.
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Itchypuss:
The problem with moisture ingres is that it's very hard to detect.. and basically impossible to notice anything on a walk-around
During heavy maintenance we put certain parts (like the elevator tab) thru x-ray to find out where in the honeycomb water pockets are, and we have also tried thermal imaging on certain parts of the airplanes structures after a flight to find water (cooler) in the composite.
If you get delamination already you can detect that with the "tap-check" but it takes quite some experience.
Regards
MB
The problem with moisture ingres is that it's very hard to detect.. and basically impossible to notice anything on a walk-around
During heavy maintenance we put certain parts (like the elevator tab) thru x-ray to find out where in the honeycomb water pockets are, and we have also tried thermal imaging on certain parts of the airplanes structures after a flight to find water (cooler) in the composite.
If you get delamination already you can detect that with the "tap-check" but it takes quite some experience.
Regards
MB
