ADIRU

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.