Changing Procedures For Detecting Corrosion In Aft Fuselage Structure

The FAA has issued a Special Airworthiness Information Bulletin (SAIB) concerning procedural changes for detecting corrosion damage to the aft fuselage structure in the area of the vacuum waste tanks on Boeing 737, 747, 757, 767 and 777 airplanes.

The FAA has received numerous reports of corrosion damage to the aft fuselage structure in the area of the vacuum waste tanks on Model 777 airplanes. This corrosion has been attributed to insufficient clean up and neutralization of leakage and spillage from the vacuum waste system. These reports document that an initial finding of corrosion damage is often followed within the year by corrosion found in close proximity. 

The waste material from a vacuum waste system spill or leak is acidic and corrosive to the airplane structure, such as skin, stringers, and frames. The waste material erodes the corrosion inhibiting compound and the protective finishes, which causes areas of bare structure that are more susceptible to corrosion. 

While the reports of corrosion have been limited to Model 777 airplanes, Boeing believes the Model 737, 747, 757, and 767 airplanes are subject to the same issue. To minimize and address this corrosion, Boeing is revising the related aircraft maintenance manuals (AMMs) and structural repair manuals (SRMs), as listed in Table 1 of this SAIB. The revisions include adding procedures for neutralizing vacuum waste; defining the correct procedures for containing, cleaning, and neutralizing vacuum waste; and adding procedures for the inspection for and removal of corrosion, and re-application of protective coatings. 

The FAA recommends that all owners and operators of the affected airplanes incorporate the revised AMM and SRM procedures when they become available.

(Source: FAA)

FMI: SAIB