Letter to NTSB regarding AA 587
 

Folks,

I noticed another thread with a lot of discussion regarding our A300 hull loss.

Thought I would repost from another forum I participate in a letter submitted by 5 former AA A-300 pilots to the NTSB requesting they reopen the investigation.

It's long, so I decided to put it in it's own thread. It's an interesting take on the accident...and FWIW, anything read regarding this event in Aviation Week should be read with a grain of salt.

There are far too many advertising dollars spent by Airbus on advertising in that publication for AW to be completely honest with their reporting.

I will be submitting this lengthly letter in separate sections.

Part 1
 

April 16, 2006

Mr. Bob Benzon
Deputy Chief, Major Investigations
National Transportation Safety Board
NTSB Headquarters
490 L’Enfant Plaza
Washington, D.C. 20594

Mr. John Hickey
Federal Aviation Administration
Aircraft Certification Service
Office of the Director (AIR-1)
800 Independence Avenue SW, Suite 800 East
Washington, DC 20591

Dear Sirs,

Beginning in the spring 2002, as pilots assigned to fly the A-300-600 for American Airlines, we became concerned about issues raised in the investigation of the crash of AA Flight 587 in Belle Harbor, NY on November 12, 2001. As the investigation went on, in order to address these concerns, several of us formed an ad hoc group to gather information and opinion from a variety of experts on aircraft rudder design, aircraft systems, aviation safety, carbon composite engineering, composite inspection methods and other topical areas of the accident investigation. After thorough analysis, we filed our concerns, as is mandated by both company policy and FAA directive, with the NTSB and FAA, along with American Airlines, in 2002 and 2003.

Among the concerns that our group made known were:

 That visual inspection techniques presently used to verify the integrity of composite materials are inadequate;
 That the structural certification requirement for the rudder and vertical stabilizer for ALL commercial aircraft should be re-evaluated, especially when considering composites;
 That A300/A310 flight control systems have had a disproportionate number of serious malfunctions/failures, resulting in uncommanded rudder movements; this is a safety concern;
 That the inherent qualities of composite materials and our present understanding of their properties may make them unsuitable for major load-bearing structures.
 That the A300 design philosophy in certain areas (e.g. -- rudder limiter and vertical stabilizer attachment) may need to be reviewed for appropriateness, when …(considering) characteristics of composite materials;
 That pilot training has been seriously deficient in regards to what constitutes safe versus unsafe application of flight controls;
 That when considering the cumulative deficiencies of composite technology, certification standards, rudder design and flight control malfunctions; serious consideration should be given to grounding the A300-600 fleet until such time as the safety of the flying public can be assured.

On March 24, 2006, the NTSB issued a Safety Recommendation that urged the FAA to, among other things, require inspections of A-300/A-310 rudders immediately, dramatically rejecting an Airbus All Operators Telex (AOT) that instead called for an inspection exemption for some A-300/A-310 aircraft and an extended period of flight on the rest of the aircraft prior to inspection or delay in repair after discovery of damage. This recommendation was remarkable because it told of delamination that had occurred on a FedEx A300 rudder, discovered when damaged in a hangar test. The discovery was significant because, according to the NTSB, it implicated intrusion into the composite material composing the rudder by hydraulic fluid as a cause for “propagation” of the delamination, and that the normal inspection methods used to insure composite integrity would not have discovered this damage:

Further examination of the disbonded area revealed traces of hydraulic fluid. Hydraulic fluid contamination between the honeycomb skin and the fiberglass composite skin can lead to progressive disbonding, which compromises the strength of the rudder. Tests on the damaged rudder also revealed that disbonding damage could spread during flight.

The investigation found that the areas specified in the AOT did not include the areas in which the disbonds were found on the incident rudder. Further, it was determined that tap tests on the external surfaces of the rudder likely would not have disclosed the disbonding of an internal surface.
--NTSB Safety Recommendation, March 24, 2006

Part 2
 

It should be noted that Airbus has long denied that internal damage to composites can remain visually hidden yet compromise the integrity of the structure significantly; they have also rejected the possibility that internal composite damage can “propagate” (a condition known in some cases as “composite fatigue.”) Also, the “tap” test indicated, in this case by the NTSB, is the type of “visual” test on which Airbus has relied as the standard for their maintenance inspections and the type of inspection that we warned was often “ineffective” in our 2002 letter to the NTSB & FAA.

Because of the past instanced documented where A-300s had experienced “uncommanded rudder” movements and that the rudder of the accident aircraft was found unattached to the vertical fin and shredded into many pieces, one theory that was discussed in the AA 587 investigation was the possibility that, as the aircraft encountered wake turbulence, the rudder began to move in an “uncommanded” fashion and the rudder itself began to break apart (this could cause a turbulent phenomena known as “flutter.”). Parties to the investigation indicated that this was “impossible” because, for the rudder to generate the loads powerful enough to break the attachment lugs on the vertical fin, they hypothesized that the rudder would need to be fully intact and whole. They also indicated that they had “found no mechanical malfunction that indicated uncommanded movement.”

However, the NTSB Safety Recommendation contained the following statements regarding Air Transat 961:

Further examination of the vertical stabilizer determined that its two rearmost attachment lugs were damaged due to the high stresses associated with the rudder failure and separation.4 These high stresses may have been dangerously close in magnitude to those that caused the in-flight separation of the vertical stabilizer during the November 12, 2001,

This statement from the NTSB is extremely important to the AA 587 accident investigation, for the following reasons:

This is the first time that:

 the NTSB has publicly considered that rudder disintegration could cause damage to the vertical fin of an A-300;
 we have been told that the vertical fin nearly separated from the A-310 aircraft involved in the Air Transat 961 incident (previous reports indicated that the damage on Air Transat 961’s vertical fin attachment points were caused by a previous incident.)
 it has been admitted by parties to the investigation that a partial rudder (as the rudder fell apart, only portions of it were placing loads on the vertical fin) could generate enough load to damage the tail to the point of failure.

Indeed, it is also of note that the NTSB is discussing “flutter” of the rudder as possibly destroying the vertical fin:

4 When the rudder separation began, the rudder started to flutter, or swing back and forth violently. This, in turn, led to the vertical stabilizer moving left and right and the stress in the lugs increasing to the point where the lugs became delaminated.

In the March 24, 2006 Safety Recommendation, the NTSB has released significant data that throws new light on some of the presumptions made in the AA 587 investigation concerning un-commanded rudder; the vulnerability of the vertical fin from damage due to “rudder flutter”; the susceptibility of rudder composite material to damage, weakening and delamination from contact and intrusion with hydraulic fluid; and the attempt by Airbus to implement wholly-inadequate—indeed, possibly irresponsible and dangerous—timeframes and ineffective methods for inspection of this extremely urgent safety issue where passenger and crew lives –if Air Transat 961 or AA 587 are any indication--could hang in the balance. This new information must be fully considered with a “fresh look” at the other factors identified in the AA 587 investigation—such as the rudder pedal design of the A-300, certification standards or the rudder design itself—so that all connected factors might be discovered, assessed and the future of air travel benefit from the conclusions.

Given this new information and for the reasons stated above, we respectfully call upon the NTSB to re-open the investigation of the crash of AA 587 immediately.

Background

In a press release on October 26, 2004, the NTSB announced that it had determined that the crash of American Airlines #587 on November 12, 2001 in Belle Harbor, NY was “created by the first officer's unnecessary and excessive rudder pedal inputs after the aircraft encountered wake turbulence, according to a final report adopted by the National Transportation Safety Board today. The Board said that contributing to the crash were characteristics of the airplane's rudder system design and elements of the airline's pilot training program.”
Additionally, the Board release stated: “The Board found that the composite material used in constructing the vertical stabilizer was not a factor in the accident because the tail failed well beyond its certificated and design limits.”
In accordance with a mandate under both federal regulation and company Flight Manual-Part One directives, a team of pilots made their safety concerns known by issuing a 70 page report to the NTSB and FAA and a follow-up letter in 2003. It is significant to note that then-NTSB Chair Marion Blakey, now the chief at the FAA, made no comment regarding the detailed concerns of pilots currently flying the A-300. In that report, the pilots stated the following concerning the inspection of composite materials used in load-bearing functions on commercial aircraft:

The information discovered thus far in the investigation has literally shaken the foundations upon which we define what is, or is not, safe. Certainly, determination of probable cause(s) will provide a measure of closure to those families who have suffered as a result of this tragedy, as well as insight into how to prevent a similar occurrence. However, some of the issues being analyzed suggest that there are areas of concern which transcend AA 587, and have the potential to impact the future of commercial aviation in a manner never anticipated. Flight 587 must now be considered the new paradigm for the airline industry.

This presentation will focus on all the issues raised so far in the investigation. It will demonstrate that nondestructive inspections (NDI) must be conducted immediately to establish baseline data and ensure the structural integrity of the existing fleet. It will call into question the use of composite materials in critical load-bearing structures. It will illustrate the risks associated with the A300 rudder pedal design given existing structural certification standards. It will bring to light deficiencies in pilot training in several areas critical to safe operations. Finally, it will underscore the pressing need to consider the grounding of the A300-600 fleet until such time as its airworthiness can be assured.

Part 3
 

It must be noted that, after the crash of AA 587 on Nov. 12, 2001, the NTSB focused immediately on pilot actions onboard the aircraft. Despite the fact that no pilot had ever been implicated in causing a crash by over-controlling the flight controls to the point of causing the flight controls—let alone the massive vertical fin-- to be damaged, in Safety Recommendation A-02-01 and -02 the NTSB issued a dire warning on pilot use of the rudder. Essentially re-defining foundational definitions of basic aviation, including the concept of Maneuvering Speed (the speed under which a pilot may exercise full control of any flight control surface without exceeding the structural integrity of the aircraft)—a foundation of pilot knowledge on aircraft limitations since the dawn of commercial aviation, the NTSB declared that successive rudder swings could cause loads on the aircraft that could indeed rip the entire tail off of the airframe. To remedy this problem, the NTSB dictated that pilots be given special “rudder training” on how to fly.

Specific areas of concern included composite inspection, uncommanded rudder and rudder design

The pilot letter went on to say:

Every pilot, regardless of what airplane they are flying now, or will be flying in the future, needs to be aware of these issues and how they affect continued safe operations. At the end of the day, we are the ones who must ensure that we are operating in the safest environment possible and are not taking unacceptable risks.

…and raised eight specific areas of concern:

We believe that the information developed in this presentation will lead to the following conclusions:

(1) That visual inspection techniques presently used to verify the integrity of composite materials are inadequate. That NDI (nondestructive inspection) technology must be developed and applied to all aircraft that utilize composite parts, both diagnostically and in preventive maintenance procedures. That all A300-600 aircraft be immediately subjected to a baseline NDI in order to ensure the structural integrity of composite materials.

(2) That the structural certification requirement for the rudder and vertical stabilizer for ALL commercial aircraft should be re-evaluated, especially when considering the properties of structures made of composites versus metal.

(3) That A300 flight control systems have had a disproportionate number of serious malfunctions/failures, resulting in uncommanded rudder movements. As a result, there are serious concerns about reliability of operation and the affect on safe operations.

(4) That the inherent qualities of composite materials and our present understanding of their properties may make them unsuitable for major load-bearing structures.

(5) That the A300 design philosophy in certain areas (e.g. -- rudder limiter and vertical stabilizer attachment) may need to be reviewed for appropriateness, when juxtaposed with certification requirements of the vertical stabilizer and rudder plus the properties and characteristics of composite materials.

(6) That pilot training has been seriously deficient in regards to what constitutes safe versus unsafe application of flight controls.

(7) That the inaccurate definition of maneuvering speed should be corrected in light of the current certification standards, and that the flying community should be made aware of the dangers of rudder reversals through detailed and specific training.

(8) That when considering the cumulative deficiencies of composite technology, certification standards, rudder design and flight control malfunctions; serious consideration should be given to grounding the A300-600 fleet until such time as the safety of the flying public can be assured.

Our letter went on to discuss each area of concern in detail. One portion, concerning the length of time that composites are used in commercial aviation, was discussed by industry experts:

Most experts agree that composites are stiff (non-ductile) when compared to metals and have differing thermal coefficients than metals at attachment points. Also, air and water are invariably entrained during the manufacturing process. As the aircraft operates over a wide range of external temperatures and pressure altitudes, these water and air deposits expand and contract, eventually causing delamination (fatigue) within the composite. These, plus other known and unknown factors affect composite material to one extent or another, ultimately reducing its utility. According to Dr. Debra Chung, Director of the Composites Research Lab at the University of New York at Buffalo, composites thought to have a useful life of 30 years may, in fact, only last 1/3 of that original estimate because they become brittle and lose elasticity. So an aircraft which is expected to operate for 30,000 cycles, may only last 10,000. Charles F. Marschner [1], a pioneer in the use of plastics in aircraft structures, reminds us that “the laws of physics and mechanics are immutable – today’s composites still have no ductility as do wrought metals.”

Part 4
 

Recent NTSB Announcement

In the most-recent NTSB Safety Recommendation, the following scenario revealed new and –according to the statements by the NTSB—surprising composite delamination on an A300 rudder:

On November 27, 2005, the rudder, part number (P/N) A55471500 (premodification 8827),1 on an Airbus A300-600 airplane operated by Federal Express, N717FE, was damaged during routine maintenance. To assess the extent of the damage, the lower rudder rib was removed and the rudder was examined. In addition to the damage that occurred during maintenance, the examination found a substantial area of disbonding between the inner skin of the composite rudder surface and the honeycomb core.2 A tap test inspection3 determined that a disbond of approximately 838 mm (33 inches) by 355 mm (14 inches), or 0.3 square meter (3 square feet), existed. Further examination of the disbonded area revealed traces of hydraulic fluid. Hydraulic fluid contamination between the honeycomb core and the fiberglass composite skin can lead to progressive disbonding, which compromises the strength of the rudder. Further tests on the damaged rudder revealed that a rapid propagation of the disbonding damage could occur during flight

As we have indicated, this is just the latest of a series of inspection orders issued by the NTSB regarding A-300/A-310 rudders. Inspections have been ongoing, and they have been revealing that some rudders have damage that needs repair…and which was not discovered under the routine inspection system.

“Following the Air Transat accident, which is being investigated by Canada with the assistance of the NTSB, Airbus issued a mandatory All Operator Telex (AOT) A300- 55A6035 specifying a one-time rudder inspection for all A-300 series airplanes equipped with pre-modification 8827 or 40904 rudders. On March 28, 2005, the FAA issued Airworthiness Directive (AD) 2005-07, requiring operators to perform the inspections specified in the AOT. American Airlines and Federal Express (the only U.S. operators of these airplanes) complied with the AD.

On November 27, 2005, the rudder on an Airbus A300-600 airplane operated by Federal Express was damaged during routine maintenance. To assess the extent of the damage, the rudder was shipped to the manufacturer's facility and examined. In addition to the damage that occurred during maintenance, the examination found a substantial area of disbonding between the inner skin of the composite rudder surface and the honeycomb core, which is located between two composite skins.

Further examination of the disbonded area revealed traces of hydraulic fluid. Hydraulic fluid contamination between the honeycomb skin and the fiberglass composite skin can lead to progressive disbonding, which compromises the strength of the rudder. Tests on the damaged rudder also revealed that disbonding damage could spread during flight.

The investigation found that the areas specified in the AOT did not include the areas in which the disbonds were found on the incident rudder. Further, it was determined that tap tests on the external surfaces of the rudder likely would not have disclosed the disbonding of an internal surface.

Airbus Had Too Much Influence in AA 587 Investigation, Remedies

One of the criticisms that the pilot group had regarding the AA 587 investigation is that the designer of the accident aircraft—and, therefore, an obviously-conflicted party- had nearly-complete control over many of the studies in the investigation, analyses and, therefore, conclusions ostensibly tasked to the NTSB. It is alarming to us, as pilots entrusted to carry passengers, that not only this conflict-of-interest is allowed to exist, but that the recommendations and, in truth, the complete decision on action-taken in many circumstances is essentially whatever the manufacturer states is required.

This is illustrated most clearly in this instance: a new aircraft manufacturer, Airbus, attempts to gain an edge on then-industry-superpower Boeing by developing and employing in active service a new material—composites—on load-bearing structures. This saves money by allowing the aircraft to weigh less, burning less fuel. Just as important: the new materials, according to Airbus, need no elaborate or expensive inspection methods to check for “fatigue”…as does aluminum. Instead, the inspections for periodic safety checks will be accomplished by mechanics using a simple “visual” inspection—looking for any marks or obvious damage on the exterior of the skin. A coin may also be used to “tap” lightly against the surface, to seek out a “thunk” that might indicate hidden damage in the interior of the composite.

More later, dinner bell ringing!

Part 5
 

Through several in-flight turbulence and other instances where other portions of the structure was damaged, only the visual or coin tap methods were used to place these aircraft back into service. Over the years, many Airbus pilots noted water intrusion problems with the composite rudder and elevator of the A-300; many were concerned that the liquid would get inside the composite, freeze into ice at altitude, breaking the composite little by little, causing “fatigue” and that the fatigue would worsen—and weaken—the aircraft structure. This is known as “propagation.”

In Nov 2001, for the first time in large-jet-commercial-aviation history, the vertical fin breaks off of an airliner; 265 people die as a result. The aircraft is one of the first aircraft to feature a composite tail; it was the same tail that endured a 1995 turbulence incident that injured over 45 passengers—the worst turbulence incident in the history of its airline. No damage was discovered on the tail using the visual inspection methods directed by Airbus.

In 1997, another A-300, AA 903, encountered an “inflight upset” off Miami. The aircraft tumbled, stressing portions of the aircraft to the point where even both engines required replacement. The inspection methods advocated by Airbus revealed no damage, and the aircraft was placed back into service. Then-confidential memos between the carrier and Airbus indicated that Airbus “suspected empennage damage” and urged “deeper inspection.” Yet, the standard was simply to inspect using the visual method. Only when the aircraft was inspected in 2002, using ultrasound, was damage found that immediately grounded it and required removal of the vertical fin for good.

Air Transat 961—2002 Warnings Unheeded Nearly Cost More Lives

Then…in March 2005, Air Transat 961 had its entire rudder disintegrate in mid-air—an eerie reminder of the AA 587 catastrophe; yet, Airbus was nonchalant, issuing directives for more visual inspections; from the recent Safety Recommendation:

Following the Air Transat accident, on March 17, 2005, Airbus issued mandatory6 All Operators Telex (AOT) A300-55A6035 specifying a one-time rudder inspection for all A-300 series airplanes equipped with premodification 8827 or 40904 rudders. The AOT recommended that operators perform a tap test on the external surfaces of the rudder skin panels and spar in specific localized areas to inspect for disbonding damage. The AOT did not recommend that a tap test be performed on the inner surfaces. On March 28, 2005, the FAA issued Airworthiness Directive (AD) 2005-07-07, requiring operators to perform the inspections specified in the AOT. American Airlines and Federal Express (the only U.S. operators of these airplanes) complied with the AD.

Even these discovered delamination on Airbus rudders that required repair. (It is noteworthy that there is an apparent omission of UPS as a US Operator of “these airplanes”…which begs the question: did UPS comply with the AOT…or, better yet, were they ever notified?)

Airbus has issued another directive after yet another A-300 rudder-disbonding incident—the rudder was found to be disintegrating on a Fed Ex aircraft. Yet, even after all of these incidents, Airbus is seemingly nonchalant, ordering an inspection that allows the suspect aircraft to fly hundreds of flights before being looked-over—again, with visual inspections:

When the rudder from the Federal Express airplane was sent to Airbus for further testing, investigators found that the areas specified in the AOT did not include the areas in which the disbonds were found on the incident rudder. Further, it was determined that tap tests on the external surfaces of the rudder likely would not have disclosed the disbonding of an internal surface. As a result of these findings, Airbus issued mandatory7 AOTs A300-55A6042, A310-55A2043, A330-55A3036, and A340-55A403, on March 2, 2006, notifying operators of applicable A-300 series airplanes that large disbonds between the rudder’s inner skin and the honeycomb core could go undetected. The AOTs call for a visual examination, within 6 months or 500 cycles, for the presence of contaminant hydraulic fluids on rudder external surfaces and the performance of a manual tap test inspection at the inner side of the rudder panels.

NTSB Counters Irresponsible Airbus Policies

This time, the NTSB was concerned enough to make the inspections, in an urgent recommendation, “as soon as possible,” with a repetitive inspection “interval”…or, subsequent re-inspections.

On March 2, 2006 Airbus issued AOTs notifying operators of applicable A300 series airplanes that large disbonds between the rudder's inner skin and the honeycomb core could go undetected, and providing guidance for inspecting the rudders. The Safety Board is recommending a more stringent compliance time than specified in the AOT and also requesting that FAA make the inspections mandatory.

More recent examinations have disclosed that hydraulic fluid can exist along the edges of the rudder's inner surface along with an accompanying area of substantial disbonding and that the inspection specified in the AOTs cannot detect the presence of the hydraulic fluid or the disbonding along the edges.

Therefore, the Safety Board is recommending that the FAA require that all operators of Airbus A-300 series airplanes immediately (possibly before further flight) comply with four Airbus All Operators Telexes dated March 2, 2006. Any disbonding to the rudder skins that occurs in the presence of hydraulic fluid contamination should be repaired or the rudder should be replaced as soon as possible, well before the 2, 500 flights specified in the AOTs. (A-06-27) This is an urgent recommendation.

The NTSB further recommended that the FAA establish a repetitive inspection interval for Airbus premodification 8827 rudders until a terminating action is developed. The interval should be well below 2,500 flights. (A-06-28)

1 Airbus identifies the configuration by which the rudder skin panels were attached to the front spar on some A300s and A310s, including the incident airplane, as premodification 8827. In this configuration, rivets penetrate the rudder’s honeycomb core to join the rudder skin panels to the front spar. This configuration is identified as premodification 40904 when used on A330s or A340s. About 400 A-300 series airplanes were manufactured with the premodification 8827 or 40904 configuration before the rudder skin panel and front spar interface was redesigned. There are no A330s or A340s on the U.S. registry.

Incredibly, Airbus dictated that, even if some damage is discovered, it should not be repaired, but allowed to remain un-repaired for an extended time period:

The AOTs further stipulate that if one disbond (per panel) is found but does not exceed 130 mm (5.1 inches) in diameter, then the panel should be reinspected or permanently repaired within 2,500 flight cycles. If one disbond (per panel) is found and is greater than 130 mm diameter but less than 200 mm (7.9 inches) diameter, a permanent repair must be performed before the next flight or an immediate temporary repair must be performed; the permanent repair must then be performed within 1,500 flight cycles. If a disbond exceeds 200 mm in diameter8 or if more than one disbond is found on one panel (even if no disbond exceeds 130 mm in diameter), the operator must immediately contact Airbus before the next flight with a detailed inspection report to obtain further instructions.

The NTSB, however, rejected the Airbus “solution” expressing that the Board:

“…is concerned that allowing an undetected hydraulic-fluid-induced disbond to exist for 500 flights, without supporting analysis or tests to better understand the safety risks, is unacceptable. Further, the Safety Board is concerned that some hydraulic fluid disbonds, when detected, would be allowed to exist for as many as 2,500 flights before the disbond is repaired. Rudder skin disbonds that are a result of hydraulic fluid contamination are particularly troubling because little is known about the progression rate once such disbonding is initiated. Contamination with hydraulic fluid will lead to a reduction in the bond strength and an overall loss in the rudder’s structural integrity, as found on the Federal Express rudder, and leaves the airplane susceptible to the type of rudder separation experienced during the Air Transat flight. The consequences of a rudder separation include reduced directional control and possible separation of the vertical stabilizer.”

The prevalence of hydraulic fluid leakage onto the surface of rudders throughout the A300-series fleet is unknown. The rate of growth of existing damage in the presence of this hydraulic fluid contamination is uncertain and currently unpredictable, and the resulting safety risks associated with the potential loss of the rudder or vertical stabilizer are severe. The Safety Board is aware that Airbus is considering exempting 24 aircraft from compliance with the current AOTs because, following the issuance of AOT A300-55A6035, these aircraft underwent additional nondestructive examinations. The Board is concerned that these tests may not have detected disbonds and that these aircraft should not be exempt from the current AOTs. The Safety Board is also concerned that there is a reasonable likelihood that disbonding damage similar to that found on the FedEx rudder, or worse, exists on other airplanes flying in the fleet today and that, given the uncertainty in the number of cycles to failure for composite rudders contaminated with hydraulic fluid, the safety risk over 500 additional flights is unacceptable. As a result, the Safety Board believes that the inspections specified in the AOTs should be conducted with the utmost urgency on all premodification 8827 rudders.

part 6
 

Significantly, in the paragraph quoted above, the NTSB states that not even the 24 aircraft that were inspected using nondestructive testing should be exempt; it is of interest to all what manner of nondestructive inspection method these 24 aircraft have undergone, as Airbus has been adamant that visual testing is all that is required on A-300/A-310 tail surfaces.

New Understandings on Composite Delamination, Effects of In-Flight Rudder Break-up

Also, the recent Safety Recommendation, the NTSB stated dramatic new findings on the Air Transat 961 incident:

Further examination of the vertical stabilizer determined that its two rearmost attachment lugs were damaged due to the high stresses associated with the rudder failure and separation.4 These high stresses may have been dangerously close in magnitude to those that caused the in-flight separation of the vertical stabilizer during the November 12, 2001,

This statement from the NTSB is extremely important to the AA 587 accident investigation, for the following reasons:

This is the first time that:

 the NTSB has publicly considered that rudder disintegration could cause damage to the vertical fin of an A-300;
 it has been revealed that the vertical fin nearly separated from the A-310 aircraft involved in the Air Transat 961 incident (previous reports indicated that the damage on Air Transat 961’s vertical fin attachment points were caused by a previous incident.)
 a partial rudder (as the rudder fell apart, only portions of it were placing loads on the vertical fin) could generate enough load to damage the tail to the point of failure.

Indeed, it is also of note that the NTSB is discussing “flutter” of the rudder as possibly destroying the vertical fin:

4 When the rudder separation began, the rudder started to flutter, or swing back and forth violently. This, in turn, led to the vertical stabilizer moving left and right and the stress in the lugs increasing to the point where the lugs became delaminated.

Experts Warn That Composites and Metals React Differently Under Load

In the original letter to the NTSB and the FAA, our pilot group asked Martin Aubury, formerly Head of Aircraft Structures at the Australian Civil Aviation Authority, about the danger of “flutter” in load-bearing composite materials like rudders or vertical fins. He responded, in part:

“…composites are more susceptible than metals to repetitive loads in the range between limit and ultimate. That is because composites do not deform plastically so there is no redistribution/alleviation of loads…”

Metal structures have the advantage that the material has approximately the same strength in all directions. So small unanticipated loads in an unanticipated direction are of no consequence. Composites are different. Fibers are oriented to carry expected load and where there are no fibers there is very little strength. An unanticipated load in unanticipated direction has far more serious consequences for composite structures than for metals.”

We also noted:

If the phenomenon explained above by Mr. Aubury…(is)true, then once again, in light of the lack of ductility of composites, the structural certification requirements for the vertical stabilizer and rudder must be re-examined.

What this means is: if a rudder begins to disintegrate, it then places unanticipated (and therefore “un-designed-for”) loads on the vertical fin. Due to these loads, is composite material as currently used on the A-300 /310 adequately-structured and tested to handle such loads? In the AA 587 NTSB hearing, on October 31, 2002, Airbus Composite Specialist Erhard Winkler explained the rudder and vertical fin destruction sequence and load factors on AA 587, documented on the transcript of that hearing on pages 941 through 952. Given the two damaged lugs on Air Transat 961, it is clear that assumptions were made in the AA 587 investigation that have not borne out in the Air Transat 961 instance.

Given the lack of foresight for predictable-hydraulic-fluid intrusion (after all, three hydraulic servos are placed inside the composite of the rudder…these servos leak on occasion)…as well as the complete failure to (first) require periodic, effective inspections that would seek such deterioration and (second) to advocate an inspection after the finding that (because it was only using the “tap” test on the exterior panels) was still insufficient to insure safety…with all of these new variables…is it reasonable to question Airbus’ insistence that the vertical fin on the A-300/A-310 is strong enough to withstand a disintegrating rudder?

And, given the proximity of hydraulic fluid around this aging composite rudder, is it not likely that hydraulic fluid will intrude into other A-300/A-310 rudders? What does this say about the design of the other tails—the A-320, A-330, A-340—that all use the same basic-designed, composite tail?

In 2002, our letter to the FAA and NTSB went on to say, regarding AA 587:

“…Did the lack of ductility of the vertical stabilizer lead to premature separation? Would a metal fin have remained on the aircraft, all things being equal? Was the flutter sound heard on the cockpit voice recorder caused by a split rudder, with one or more parts free-floating? There is an AD (enclosure 3, #25) which refers to “freeplay” of the elevator causing severe vibrations in the back of the airplane. Could “freeplay” in a rudder cause similar vibrations which in turn were picked up on the voice recorder as a “flutter” sound?

Uncommanded Rudder

Finally, we must address the issue of “un-commanded” rudder. In a variety of incidents, many documented in the A-300 pilot group’s letters to the NTSB, FAA, American Airlines and the Allied Pilot’s Association, nearly 30 episodes of the rudder moving without pilot input on A-300 or A-310 aircraft have occurred. In the Air Transat case it is clear that the pilots did not manipulate the rudder in any way—meaning, the rudder moved in an “un-commanded fashion.” In May, 1999, AA Flight 916 took off out of Miami and encountered a severe “un-commanded rudder” event. A bulletin that was later issued to American pilots warned that the “uncommanded rudder” was swinging “up to 12 degrees of deflection.” (It should be noted that the rudder swings on AA 587 were less than this degree…which, according to the NTSB, was enough to rip off the vertical fin.) The pilots were –and are—very concerned about “un-commanded” rudder, as the “rudder training” called-for in the NTSB Safety Recommendation A-02-01 and -02 for all pilots will be of little use if the aircraft rudder begins swinging in an un-commanded fashion. It should be remembered that the A-300 pilot group issued several recommendations in 2002—including this one, regarding un-commanded rudder and composite design and inspection issues:

8) Finally, based on the concerns listed below, serious consideration must be given to grounding the entire A300-600 fleet until its airworthiness can be assured.

(a) Certification requirements of the vertical stabilizer and rudder are insufficient to prevent structural separation of the tail assembly under certain “rudder reversal” conditions.

(b) There have been documented cases of delamination in the elevators, rudders and vertical stabilizers, compromising the integrity of these structures. Nondestructive technology is not being used and baseline date has not been established to ensure the integrity of composite structures on an ongoing basis.

(c) There have been a disproportionately high number of documented cases of uncommanded rudder inputs which have, at times, led to large rudder displacements.

(d) The rudder limiter/pedal design is ill-conceived and its limitations may contribute to, rather than prevent, inadvertent “rudder reversals”.

(e) The A300 vertical stabilizer design should be reevaluated as to its method of attachment to the fuselage, in light of its composite structure.

It is worthy of note that in a portion of the investigation, the NTSB studied the possibility of a rudder disintegration (“Airbus Report AAL 587 Crash: Study of Aeroelastic Scenarios; SA-522, Exhibit 7U.”) Although this report considered three possible scenarios, it did not consider the scenario that occurred on Air Transat 961; it also made assumptions about rudder damping and rudder limiting functions that have since been reconsidered. Nonetheless, it concluded that the effect would be “strong instability” in at least one rudder disintegration scenario they did consider.

part 7
 

Air Transat 961: Tail Damage Exceeded “Fail-Safe”

During the AA 587 crash investigation, after it was revealed, using ultrasound in 2002, that the aircraft from the 1997 incident in MIA (AA 903) had suffered a broken attachment lug for its vertical fin, Airbus made repeated statements regarding the “fail safe” certification requirement that one lug of the vertical fin could be completely broken and the aircraft was still “safe to fly.” These statements were alarming as Airbus seemed to completely ignore the limitation that the “fail safe” design only ensured a safe recovery after the damage to the single lug—not continued operation for nearly five years. At that time, the pilot group made the point several times that, if you do not use effective inspection methods to discover hidden damage within the composite, there would be no way of knowing if damage had occurred to one lug, or multiple lugs. The NTSB revealed in this latest announcement that Air Transat 961 suffered severe damage to two lugs. Whether the rudder broke off cleanly or caused “flutter” it is clear that Air Transat 961 demonstrated that even pieces of a rudder can cause sideloading significant enough to severely damage a vertical fin beyond even the “fail safe” margin.

Particularly in the above paragraph “b”. the NTSB has stated quite clearly that in this recent incident, Airbus has issued a directive that did not adequately address the concern about the delamination of composite material and the inspection methods to clear the aircraft for safe flight; it chided Airbus for inappropriately suggesting that certain aircraft be exempt from the inspections; and it was in open denial of the Airbus directive to continue flying even if some rudder surfaces had been exposed to hydraulic fluid as it shared the same concerns that the Airbus pilots expressed in 2002 about “baseline data has not been established to ensure the integrity of composite” in the situation that Airbus had attempted to apply. The patched middle attachment lug of AA 587’s vertical fin had no “baseline data” on which to continue under service after having 21 metal bolts drilled though the monolithic carbon-carbon fiber stand structure…nor did the aircraft from AA 903, which flew for five years with a cracked lug. The Chief Scientific and Technical Advisor in the area of Composites, Dr. Larry Ilcewicz, testified at the NTSB hearing in 2002 that:

“In the case of the accident in 1997, because we had an unknown load level that, as a conservative approximation, could have been within 1% of failure. The decision was made that we do not have a database where that tail had been loaded to within 1% of failure and then taken for a lifetime’s worth of load, and so the decision was made to remove it from service.”

New Data

The NTSB, in the March 24, 2006 Safety Recommendation, has released significant data that throws new light on some of the presumptions made in the AA 587 investigation concerning un-commanded rudder; the vulnerability of the vertical fin from damage due to “rudder flutter”; the susceptibility of rudder composite material to damage, weakening and delamination from contact and intrusion with hydraulic fluid; and the attempt by Airbus to implement wholly-inadequate—indeed, irresponsible and dangerous—timeframes for inspection of this extremely urgent safety issue where passenger and crew lives –if Air Transat 961 or AA 587 are any indication--could hang in the balance. This new information must be fully considered with a “fresh look” at the other factors identified in the investigation—such as the rudder pedal design of the A-300, or the rudder design itself—so that all connected factors might be discovered, assessed and the future of air travel benefit from the conclusions.

Pilots: Re-open AA 587 investigation

Given this new information, we call upon the NTSB to re-open the investigation of the crash of AA 587 immediately.

Captain Rxxxxx Txxxxxxxx
Captain Pxxx Cxxxxx
Captain Gxxxx Sxxxxxx
First Officer Txxx Wxxxxxx
First Officer Jxxxx Gxxxxxxx

Thanks for the post! If you want, I could store the letter in the downloads section of the main site.

Cheers -

As you wish...

Regards,

ADIRU

That was a very interesting read. I apprecaite you taking the time to post that information.

Out of curiosity, what is the concern with the current rudder pedal design? Does Airbus(t) want to limit the travel of them, or something along those lines?

I couldn't figure out what they were talking about with the peddels either. The rest was very clear. Would like to know why we are not doing anything about it... since airbus dos not care.

Flight 961 Rudder Failure
 

ADRIU:
This report was sent to the FAA ) 5-22-2005. I sent it overnight and have postal receipts.
After a few phone calls I did receive a reply, negative.

The Fed X rudder damage prompted NTSB to insist on immediate inspections using tap test on both inner and outer skins as I insisted on below.
Tap tests are not visual they are acoustic and reliable.

I believe that moisture ingression caused the skin to core disbonds and the hydraulic fluid penetrated. If skydraul hydraulic oil attacked the facing or skin resin then penetrated to the core; this would indicate a bad choice of facing resin. This is not good as there is no fix except isolation of oil from the laminate.

Flight 961 made it clear that if that rudder was on Flight 587 and experienced that turbulence, it would have broke away from the tail.

So----- the pilots experience the turbulence and apply force to the weakened rudder, the rudder bends under the load and the ship does not respond as expected so more or reverse rudder is used, the rudder deflects more and “BANG” the rudder breaks away. Then the ship turns latterly, and “BANG” the tail breaks away.

Back to Flight 961, after the rudder broke away, and for some reason the pilot might have applied rudder one way or the other: Would the black box record movement or the FDR record movement even though the rudder was missing? Would this indicate rudder movement even though the rudder is not attached?

ADRIU, Please read below and see if it works for you. It’s worth the time.

Also I would appreciate some help on how to post and quote on the site.

Gene Schulte


Flight 961 Rudder Failure

05-22-2005

First, composites are good choice for application on many aircraft structures.

Rudder structures are good candidates for applying a well designed honeycomb sandwich composite structure.
The rudder on the A310 is honeycomb sandwich. It is not foam.

A honeycomb sandwich structure or, for that matter an aluminum structure will fail in service if, never inspected!

Honeycomb sandwich structures are prone to absorb water over a period of time (Moisture ingression due to altitude cycling) and when it freezes, it will cause progressive facing to core disbonds!

These sandwich structures meet design and safety requirements providing an adequate inspection program is in place to ensure that core to facing disbonds are discovered at onset. Then, repair dispositions are made using approved repair procedures or rudder replacement. What are the Airbus inspection requirements, inspection schedule and the test methods required by Airbus to discover facing to core disbonds on the inner and outer facings of the rudder specified prior to this failure??

To my knowledge, Airbus does not require any inspection of the tail and rudder to be performed prior to five years in service. After five years only visual inspection is required.
Ref. Air Safety week, June 17, 2002, page 3 and July 29, 2002, page 3. I don’t recall the source of the “visual inspection after five years of service”.

Barbara Crufts, an Airbus spokesperson, said visual inspections were “the normal procedure” and insisted Williams’s case was unproven. “You quote him as an expert. But there are more experts within the manufacturers and the certification authorities who agree with these procedures.” She disclosed that the aircraft used in flight 961 — which entered service in 1991 — had been inspected five days before the incident. She said did not know if the rudder had been examined

We all know that the pilot on a walk around inspection can only tell if the rudder is attached.

Airbus requires only visual inspection of the tail and rudder. Facing to core disbonds, the primary modes of failure on the rudder will not be discovered by close up visual inspection. A one inch square core to facing disbond will not be detected by visual inspection. When water freezes in the core cells it expands enough to break the facing to core bond in that area. The facing remains in contact with the core after the ice melts. There may be a .001 of an inch or less space between the facing and core and the facing is not bulged in that area. This .001 in. gap is not detectable visually. This one inch square disbond will increase in size over a period of time and could grow to a 2 x10in.area and not be detected by visual inspection.

Once a disbond occurs an adjacent disbond will occur in lesser time than the first. Now the stress in the facing must go around the disbonded area, and causes a stress riser at the adjacent core to facing bonds. Also a peel force is introduced as the facing will try to buckle over the disbonded area, thus disbonding occurs at a much faster rate as the disbond area increases.

These disbonds should be detected at onset before large areas of the rudder are affected. When skin waviness is detected visually, this is a good indication that a large area of disbonding has occurred and the structure is not flight worthy. Small disbonded areas should be detected at onset by some means of testing other than visual: because you can’t see them. Fix these small disbonds before the large areas of skin can be seen visually indicated by waviness.

The manufacturer will specify the maximum area of core to facing disbonds allowed for the rudder to stay in service. This area will be relatively small. The largest single disbonded area allowed, my guess, Five inches square on each side of a sandwich panel or 20 square inches per rudder.

Large disbonded areas put forth in some discussion forums as acceptable that include a total disbonding of one face form the core or 30% of the total bonded surface will cause the rudder to separate form the tail.

Reference FAA, AD 97-04-07 allows up to 5000 square cm or 1,968 square inches of disbonds per rudder. The rudder is constructed of two sandwich panels consisting of an outer and inner facing each or four bonded facings per rudder. Allowable disbonds of approx 500 square inches per bonded facing amounts to a 10in. X 50in. disbond per facing. A 10 in., X 50 inch disbond on one facing would be enough to unravel the rudder.

These FAA high numbers allowed for disbonds are not realistic and show a lack of understanding of how sandwich structures work. Are we talking mm?

In short, core to facing disbonds are the primary cause of failure in sandwich structures.
It follows then, that engineering provides an inspection method applied to the rudder at scheduled inspection intervals to determine if facing too core disbonds exceed the maximum allowable disbonded area allowed by engineering.

What if any inspection methods other than visual methods were applied to this rudder over the last 13 years of service?
A tap test applied to the exterior facings will easily detect facing to core disbonds on the exterior surface.
The interior facings are closed to tap tests. What test do we use to determine disbonds on the inner surface?
There should be an ultra sound test to do this or some test, specified by engineering that will accurately and in a timely manner discover disbonds at the inner facings.

There is one Airbus test called ELCH “Repetitive Elasticity Laminate Checker” It is designed to discover core to inner facing disbonds. This seems to be sensitive to test procedures as a vacuum is applied to the outer skin and pulls it in into the cavity above. The amount of deflection of the skin then indicates if there is a disbond.
Overlaps of the skin prepreg could show less deflection indicating a good bond. Another problem is porosity in the skin which could change the readings.

If there is no record of testing for disbonding history for this rudder for the last 13 years: It’s highly possible disbonding exceeded the maximum area allowed by engineering.

Please click on the link below for honeycomb sandwich info from Hexcel.
Please click on Benefits on the right and click Attributes and Properties.




http://www.hexcelcomposites.com/Mark...n_tech/p04.htm



Below, is shown the upper part of Flight 587 rudder. The outer facing (skin), honeycomb core and inner facings are shown.

See photo No. 5
http://www.usread.com/flight587/Coast_Guard_Pix.html

The #7 hinge is not connected but is attached to tail with pieces of the rudder attached. The tail photo is not shown.



If #7 hinge was still attached to the A310 tail with bits of the rudder spar attached as the other hinges are, then the cause of separation from the tail would point to unraveling of the rudder. But!!!!! The cause of the #7 hinge failure at the rear spar of the tail must be determined before cause of the separation can be resolved.

The current ADs requiring tap test on these rudders should be withdrawn or revised to include a test method that will discover outer and inner facing to core disbonds.

My advice to the pilots is to insist, through your Flight Safety Organizations, on a full report detailing the inspections conducted to date on the rudder of your aircraft. If the report documents visual inspections only: and show no history of testing to determine if disbonding is within engineering allowables:
Don’t fly the ship.

Any comments are appreciated:

Thank You:

Eugene Schulte
261 PR 3333
Bridgeport, TX 76426
940-683-2855
[email protected]


Enclosures:

U.S. Read-coast Guard Pix of Flight 587 Rudder.
(2) Hex Web Honeycomb Sandwich Design Technology
Air Safety Week March 21, 2005 Publication, “A310 Losses Rudder, Prompts Fleetwide Inspections, Inquiry”.
Airbus “Repetitive Elasticity Laminate Checker”











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