On the afternoon of Wednesday, July 29, 1992, nearly a year and a half after the crash of Flight 585, Ron Schleede received a phone call that made him very angry. The caller told Schleede, who was chief of the Major Investigations branch of the NTSB, that a Boeing 737 rudder problem was being independently investigated by United Airlines—that is, the airline was conducting an investigation without reporting it to, or sharing any information with, the NTSB. Besides United, this “private” investigation involved Parker Hannifin, the company that produced many of the hydraulic components fitted to the 737. Parker Hannifin had just confirmed to United that under certain conditions a hydraulic component in the 737’s rudder mechanism could unexpectedly force the rudder into maximum deflection, a so-called hardover. Schleede was furious that no one had thought this information was important enough to share with Al Dickinson, who headed the 585 investigation and reported to Schleede. Although there was no direct evidence that a full rudder deflection drove Flight 585 into its final inverted S-shaped curve into Widefield Park, everyone involved in the investigation knew, or should have known, that the “hardover hypothesis” was perhaps the simplest and clearest explanation for what had happened.
KeywordsFlight Control Hydraulic Fluid Servo Valve Hydraulic Component Safety Recommendation
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