U.S. FAA revealed last week that it "recently required the nation's airlines to disable the oxygen generators located in all aircraft lavatories to eliminate a potential safety and security vulnerability." Airlines completed the work on 6,000 aircraft by March 4, the agency said in a statement. It did not explain what danger the generators posed, but the concern was clearly that a knowledgeable terrorist could ignite the contents of the container while in the lavatory.

"The FAA, along with other federal agencies, identified and validated the potential threat, then devised a solution that could be completed quickly," FAA stated. "In order to protect the traveling public, the FAA eliminated the problem before making the work public. Had the FAA publicized the existence of this security vulnerability prior to airlines fixing it, thousands of planes across the U.S. and the safety of passengers could have been at risk."

The agency said it is working with aircraft manufacturers "to design, certify and install a new lavatory oxygen system on all of the different aircraft types and configurations in the U.S. fleet." Until new systems are in place, airlines are being directed to "reinforce crew emergency procedures" calling for flight attendants to "check whether the lavatory is occupied following any event where oxygen masks are deployed in the cabin."

The 1996 ValuJet DC-9 crash resulted from a fire caused by oxygen generators that ignited while being transported in the aircraft's cargo hold.