Date: 16 Dec 96 03:15:38 From: "P. Wezeman" <email@example.com> Organization: The University of Iowa Followups: 1 2 3
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On Saturday, December 14, print and broadcast news media reported that the National Transportation Safety Board had made several recommendations to avoid a repetition of the type of mishap that destroyed TWA flight last July. They recommended that: 1. Inside fuselage fuel tanks on airliners be thermally isolated from sources of heat inside the plane. 2. Such fuel tanks have added to them while on the ground such amounts of cold fuel as needed to ensure that the temperatures inside the tank not get so high as to form an explosive fuel vapor-air mixture. 3. Over the longer term airliners be equipped with systems to keep the ullage spaces in such tanks filled with nitrogen gas instead of air. I had the impression that they were talking about a retrofit to present aircraft. They also announced that they consider it possible that the explosion was triggered by a static electricity discharge. I do not have any informants inside the NTSB, but it seems to me that their recommendations are consistent with long standing policy that it should always take at least two separate and independent failures to cause the loss of an airliner. In this case, fuel tank explosions were thought to be prevented by the fact that there was no source of ignition in the tanks and that jet fuel was too non volatile to form an explosive mixture at any temperature that would be encountered in normal operation. Presuming that flight 800 was destroyed by one of the several ignition sources that has been proposed, unless we can find and identify the exact cause it will be very hard to guarantee that it couldn't happen again. If the cause is some small component it may be that it will never be found, or that it could take years. However, it is still possible to have redundant protection from fuel tank explosions by ensuring that in normal operation there is no oxygen in the tanks, and, of course, also taking steps to keep the fuel from becoming overheated. As far as I could tell from the news stories, the nitrogen system was only considered to be necessary for the fuselage tanks, but it was recommended for all airliners with such tanks and not just for 747s. One presumes that the search for the specific cause of the destruction of flight 800 would continue regardless. Peter Wezeman, anti-social Darwinist "Carpe Cyprinidae"