The National Transportation Safety Board today urged the Federal Aviation Administration to order inspections of the inner skin of the composite rudder surfaces of certain Airbus A-300 series airplanes.
The safety recommendations (one of which is classified as urgent by the Safety Board) address a safety issue identified during the investigation of damage found during an inspection of a rudder from a Federal Express A300-600 airplane. The Board noted that this incident might have applicability to a more serious rudder separation that occurred last year.
"The Board believes that this urgent recommendation, if acted upon quickly, will go a long way to prevent a catastrophic failure of the rudder," NTSB Acting Chairman Mark V. Rosenker said.
On March 6, 2005, an Airbus A310-300, operated by Air Transat as flight 961, experienced an in-flight separation of its rudder shortly after departure from Juan G. Gomez International Airport in Varadero, Cuba. The flight returned to Varadero, where it landed uneventfully. Upon landing, the crew discovered that most of the airplane's rudder had separated in flight with only the bottom closing rib and the spar between the rib and the hydraulic actuators remaining.
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 premodification 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.
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)
It is estimated that these recommendations concern about 400 aircraft in Airbus's worldwide fleet.