The U.S. Federal Aviation Administration (FAA) (Washington, DC) recently issued a special bulletin advising owners, operators, and maintenance personnel of The Boeing Co. (Chicago, Illinois) aircraft of procedural changes to detect corrosion damage on aft fuselage structures near vacuum waste tanks.
The changes apply to Boeing 737, 747, 757, 767, and 777 airplanes.
“We have received numerous reports of corrosion damage to the aft fuselage structure in the area of the vacuum waste tanks on Model 777 airplanes,” the FAA writes in the bulletin. “This corrosion has been attributed to insufficient cleanup and neutralization of leakage and spillage from the vacuum waste system.”
The FAA explains that the 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 FAA writes. “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 reports of corrosion have thus far been limited to Model 777 airplanes, Boeing believes its Model 737, 747, 757, and 767 airplanes are subject to the same issue, according to the FAA.
To minimize and address the corrosion, Boeing is revising the related aircraft maintenance manuals and structural repair manuals. 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 and removal of corrosion and the re-application of protective coatings.
The FAA recommends that all owners and operators of the affected airplanes incorporate the revised procedure manuals when they become available. The planned release dates
can be found here, with all expected to be complete by October 2017.