Transcript of Hearing 12/12/97 - TWA Flight 800 Investigation

13171234be for a long period.You mentioned, Mr. Thomas, that you -- thatin some of your later 747’s that some of the lowpowered wiring was shielded?56WITNESS THOMAS:CHAIRMAN HALL:Correct.Could you explain the78difference to me between the later model 747’s and theearliers in regard to that, the shielding?9WITNESS THOMAS:As we described yesterday, I10believe it was, there is two -- the reason for1112shielding is low energy EMI,wiring.or coupling between other131415161718192021We have shielding on the Honeywell gagingsystem because when we introduced –– I forget whatparticular feature it was, onto the airplane, itintroduced some low level noise.On the 747-400’s and 757-67 airplanes, thegaging system works on a slightly different principal.The Honeywell system works on sending a -- basically, ahigh frequency signal to the probes, and you can filterout noise on that high frequency by –– just like you22tune a radio.You can have filtering on the system.2324The newer systems in effect pulse the probes,and there is a lot of information on that pulse. We25look for resistance,we look for capacitance, we –– inCAPITAL HILL REPORTING, INC.(202) 466-9500