Boeing is revising maintenance procedures for most of its in-service aircraft to address growing problems with corrosion damage caused by spillage from vacuum waste tanks, and FAA is urging operators to incorporate the changes into their maintenance programs.
The moves, which affect 737s, 747, 757, 767, and 777s, stem from “numerous” reports of aft fuselage corrosion damage on 777s, FAA explains in a special airworthiness information bulletin issued April 13. The corrosion has been tied to “insufficient clean-up and neutralization of leakage and spillage from the vacuum waste system,” the agency said
"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 agency explained. "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 have involved only 777s, Boeing believes the same risks apply to the other models. The manufacturer is revising aircraft maintenance manuals and structural repair manuals, adding procedures for “neutralizing” vacuum waste, detailing the correct procedures for cleaning and containing the waste, and adding corrosion-removal and prevention steps.
The updates started with the 777 and are complete. Revised instructions for the remaining fleet types are expected to be done by October.
FAA said the issue, while a concern, does not warrant an airworthiness directive.