January 2002 - Federal Express Flight. A pilot flying an Airbus A-300 freighter "complained about strange ‘uncommanded inputs’ – rudder movements which the plane was making without his moving his control pedals. In FedEx’s own test on the rudder on the ground, engineers claimed its ‘actuators’ – the hydraulic system which causes the rudder to move – tore a large hole around its hinges...." [44]
The mechanics "found that hydraulic fluid had caused some of the composite material in the plane’s rudder to ‘disbond,’ or come apart." [45]
The mechanics also "found bent and broken rudder control system components, as well as associated disbonding of the composite tailfin." The mechanics "unearthed a synchronization issue, wherein hydraulic pressure pulses from different sources can get out of phase." The resulting "oscillation was felt as a sustained vibration, and then a loud bang was heard." [46]
The rudder assembly "may represent a telltale of "yaw oscillation." NTSB investigators immediately focused on the implications of the damaged/broken rudder control components found on the FedEx airplane and their possible relevance to the AA587 crash. "It appears that the system damaged the rudder. ‘That is not supposed to happen; the system should break out first,’ states an NTSB official." [47]
March 2005 - Aboard Air Transat Flight 961 Over the Caribbean Sea. On March 6, 2005, an Airbus A310-300 with 262 passengers was cruising at 35,000 feet when the "flight crew heard a loud bang followed by vibrations that lasted a few seconds. The aircraft entered a repetitive rolling motion, known as a Dutch roll, which decreased as the aircraft descended to a lower altitude." [48]
The crew was able to turn the plane around and return to Varadero, Cuba, where they carried out an uneventful landing. Upon arrival, it was discovered that the aircraft rudder had been torn off the plane, except for its "bottom closing rib and the length of spar between the rib and the hydraulic actuators." [49]
"An examination of the vertical tail fin of the aircraft, to which the rudder is attached, determined that the two rearmost fin attachment lugs were delaminated, likely the result of stresses that existed during the rudder separation." [50]
In its report about the occurrence, The Transportation Safety Board of Canada (TSB) observed, "At the time of this occurrence, composite materials in general were from a maintenance perspective, believed to have a no damage growth design philosophy. It was also believed that from a fatigue point of view, more frequent inspections of composite materials would not prove to be more effective." [51]
The TSB report recommended:
"The separation of the rudder from Air Transat Flight 961 and the damage found during the post-occurrence fleet inspections suggest that the current inspection program for Airbus composite rudders may not be adequate to provide for the timely detection of defects. In addition, the recent discovery that disbonds could grow undetected and the increasing age of the composite rudders suggest that increased attention is warranted to mitigate the risk of additional rudder structural failures. The consequences of a rudder separation include reduced directional control and possible separation of the vertical tail plane." [52]
TSB further recommended that "a detailed inspection of the drainage path of the rudder for blockage be added to the current inspection program to insure that there is adequate drainage." [53]
On March 27, 2006, TSB reported that the required inspections "found examples of disbonds, damage around hoisting points and trailing edge fasteners of the rudder, corrosion and abrasion at hinges, seized hinges, hinges with excessive free play, water ingress, and hydraulic fluid ingress." [54]
TSB commenced "work with the National Research of Canada to identify suitable inspection techniques that will detect failures in composite materials." [55]
November 27, 2005 - Aboard Federal Express Flight. During routine maintenance, the rudder on an Airbus A300-600 was accidently damaged. To access the extent of 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. [56]
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 the flight." [57]
The NTSB determined that existing "tap tests" on the external surfaces of the rudder were unlikely to disclose "the disbonding of an internal surface." The NTSB recommended a more stringent compliance time for inspections and requested that the FAA make the inspections mandatory. [58]
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