planemad2,
Water ingress into honeycomb leading to delamination as the water expands into ice as an aircraft climbs to altitude is a very real problem. This is what I thought may have occurred in this case myself.
As I said above structures can and have failed without design loads being exceeded, in terms of composites I see this a method how this can happen. The delaminating normally occurs between the honeycomb core type material and the skin.
I am not aware of this type of delamination being a problem in areas where you have multiple layers of composites, such as what is used for attachment points, like the rear lug on AA587. Multiple layers of composite are basically a mixture composite (or other) fibers and an epoxy type resin matrix, this does not ingest water like honeycomb.
On skin panels, like on control surfaces honeycomb is used as a spacer between layers of composites, to keep the layers separated and provides the stiffness. If this was to delaminate it would do so between either/or the inner or outer skin and the honeycomb, and is not structurally that significant. The delamination would not extend to the bond between the attachment point and the skin, or solid ribs as these would be layers of composites.
Whilst it may not be structurally significant, it can be aeroelastically significant as it changes the mass distribution over the hinge line which can lead to other aeroelastic phenomena.
The presence of delamination is easily checked whenever an aircraft returns from a flight with a thermal camera, cold spots on control surfaces will remain cold after landing indicating the presence of ice inside the surface.
I agree that the OAT was +6 deg C when AA587 took off, and the wake turbulence occurred at 3300 ft, which would put it at about 0 deg C, however one must also bear in mind what Dr Matthew R. Fox said in his materials investigation to the AA 587 enquiry. He said that the composite fractures were examined at high magnification using scanning electron microscopy. The lug area fractures were photographed at more than 300 locations, and over 500 square inches of crack surfaces examined at high magnification, with no observed pre existing defects, including fatigue.
Some of the pilot community use the term “rudder reversal”, I do not believe this was actually stated, “rudder reversal” is an aeroelastic phenomena like flutter.
A310GUY
Don’t forget the wake turbulence was correct by the F/O with a recorded control wheel inputs of over 62 degrees right, and 78 degrees left,
combined with numerous recorded rudder pedal inputs (more than the two you stated) with over 6 inches of rudder pedal displacement. The sole use of rudder did not induce all the loads on the airframe, as the secondary effects of roll also played a part.
To quote the AA A300 fleet standards manager at the NTSB “Most pilots think that a limiter on some system will protect…the pilot from exceeding whatever parameter that limiter is limiting. And in this case…and it’s
not unique to Airbus aircraft…the pilots think that the rudder limiter will protect the aircraft structurally, and if it can’t…they think…that there would be a limitation or a warning or caution or a note that would indicate…that the rudder limiter couldn’t protect [the aircraft] structurally.”
Flight Safety,
As I said in a previous post, I was unaware of facts being made public, that does not preclude them being available elsewhere. The aircraft was largely intact on arrival, crew are able to give statements.
