Airworthiness Directives; Boeing Model 747-400 Series Airplanes

The FAA is revising an existing airworthiness directive (AD) that applies to certain Boeing Model 747-400 series airplanes. That AD currently requires inspecting the support bracket of the crew oxygen cylinder installation to determine the manufacturing date marked on the support, and performing corrective action if necessary. This new AD retains all the requirements of the existing AD and expands the applicability of the existing AD to include certain airplanes that are not on the U.S. Register. This AD results from a report indicating that certain oxygen cylinder supports may not have been properly heat- treated. We are issuing this AD to prevent failure of the oxygen cylinder support under the most critical flight load conditions, which could cause the oxygen cylinder to come loose and leak oxygen. Leakage of oxygen could result in oxygen being unavailable for the flightcrew or could result in a fire hazard in the vicinity of the leakage.