Monday, September 13, 1999

Boeing 737
rudder woes ‘could
be catastrophic’

Associated Press


SEATTLE -- Efforts to fix rudder problems in the Boeing 737, the world's most common jetliner, have not eliminated malfunctions that "could be catastrophic," the National Transportation Safety Board concluded.

The board detailed its investigation in a July report on the 1991 crash of United Airlines Flight 585 in 1991 in Colorado Springs, Colo., and the crash of USAir Flight 427 near Pittsburgh in 1994. All 157 people on the two 737s died. The 737 is the only commercial jet with a rudder controlled by a single hydraulic valve. Other jets have multiple valves that can compensate for each other if one jams.

The single valve has shown a tendency to jam, causing rogue deflections of the sort that apparently affected a Metrojet flight in February, officials said.

The crew reported that the rudder pedal appeared to move without being touched, at one point causing the 737-200 to turn to the right. The crew managed to land safely, partly by shutting down the plane's main hydraulic system. Had the rudder remained jammed, the plane could have rolled into a high-speed dive.

The NTSB report lists 112 such "rudder events" on Boeing 737 flights in the past two decades. "The 737 series airplanes . . . remain susceptible to rudder system malfunctions that could be catastrophic," the report said.

Redesigning the rudder -- the largest moving part of the jet -- could cost Boeing hundreds of millions of dollars and cause uncounted airline disruptions for modifications. There are 3,111 Boeing 737s in use worldwide, as many as 800 in the air at any given time. Boeing and Federal Aviation Administration officials say an upgraded rudder valve installed over the past two years on all 737s registered in the United States and many registered abroad have made a safe jet even safer.

(In Hawaii, Aloha Airlines has a fleet of 19 737s. Tom Yoneyama, an Aloha spokesman, said the airline completed all required rudder upgrades ahead of schedule and strictly complies with safety directives.)

The 737 crashes on average less than two times per million departures, a record Boeing says rivals that of any other commercial jet.

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