forward Sept.

forward Sept. 28 a Delta Air Lines [DAL] B737 at 31000 ft upon a flight from Washington, DC to Orlando, Fla., experienced an uncommanded yaw and revolve of some 50 degrees to the left At first, it was feared that this was another case of a 737 rudder excursion, as it were, of the symbol believed to have resulted in the fatal 1994 crash near Pittsburgh of USAir Flight 427 (see ASW, March 29) However, according to sources, this late incident with the Delta jet expect like a failure of the yaw damper; relevant constituents were replaced, the problem was solv and the airplane is now back in service. The composings that were removed have been get backed to the manufacturer for analysis.

However, and this is important, if the case had involved an outof-control rudder power command unit (RPCU), a successful recruiting would not have been considered a catastrophic situation, based forward the Federal Aviation Administration's (FAA) latest interpretation of the time That viewpoint is contained onward page 167 of the National Transportation Safety Board's (NTSB) final report of the USAir flight 427 accident, which was published freshly (NTSB Report No. #AAR-99-01). This FAA explanation of the time "catastrophic failure situation" was offered:

"A catastrophic failure is common that will always result in an accident. In the case of a dual slide jam in the rudder PCU this condition will not always conclusion in an accident. The airplane is full controllable in that configuration in every part much of its flight coma Thus, it is not a catastrophic occurrence as defined by FAA regulations and policy. Not being catastrophic, the regulations do not require that the dual slide jam be extremely improbable. Nevertheless, with the service history and the number of hours of operation in succession the 737, the FAA believes a dual slide jam has been shown to be extremely improbable and in compliance with the regulations."

A plain reading of this statement looks to be saying the FAA will allow a potentially catastrophic condition to exist because it's not always fatal. For example, should a rudder hardover fall out at 37,000 feet, the pilot may have the time and the port of mind to react and cure the airplane; should the rudder choice to shift to its deflection limit, and to the same side as the failed engine in an engine-out situation during takeoff, the pilot probably won't have time to react. However, the FAA believes this "window of vulnerability" is a period of just about 20 seconds and is therefore an acceptable risk. Hence, the corollary to the FAA's latest interpretation of the boundary "catastrophic failure condition" seems to be that it's simply catastrophic if it kills each time.

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