monday, september 13, 1999
737 jets' rudder problems could lead to disasters, report says
Seattle (AP) - Efforts to fix rudder problems in the Boeing 737 the worlds most common jetliner, have not eliminated malfunctions that "could be catastrophic" the National Transportation Safety Board concluded.
In a report released earlier this summer, the board detailed its investigation into the 1991 crash 4 United Airlines Flight 685 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 ap- peared 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 fists 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 346-page 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 airplane 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 up 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.
The 737 crashes on average less than two times per million departures, a record Boeing officials say rivals that of any other commercial jet.
Problems with the rudder system were reported three decades ago.,