737 Rudder Problems Remain?
S E A T T L E, Sept. 13 -- 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.
In a report released in July, the board detailed its investigation into 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.
Single Valve Danger
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 346-page report said.
Replacement Cost Considerable
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 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.
The 737 crashes on average less than two times per million departures, a record Boeing officials say rivals that of any other commercial jet.
In March, the safety board requested that the FAA convene a panel to consider further rudder changes.
Boeing Ready to Continue Changes
“We await (the panel’s) findings and recommendations of what, if anything, can be done to improve the rudder system,” Boeing spokesman Russ Young said.
It’s not known whether rudder problems contributed to the crash of a 737 in Argentina on Aug. 31 or of another in Turkey in April. Flight data tapes from those planes and 737s that went down in Indonesia in 1997 and Peru in 1998 have not been recovered.
Problems with the rudder system were reported three decades ago.
Engineers at Bertea Corp., which contracted with Boeing in the late 1960s to mass-produce the 737’s rudder valve in Irvine, Calif., obtained patents in 1969 and 1982 on devices to correct the jamming problem but found no buyers.
“One failure ... occurs when the valve becomes stuck or jammed,” the 1969 patent cautions. “This may be the result of contaminants ... warpage, thermal expansion or contraction of the elements of (the valve) or numerous other reasons.”
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