187 Rudder Mishaps Reported With 737s : Aviation: NTSB gets list of incidents since 1970, sharpening focus on two unsolved jet crashes. Boeing says it’s not a continuing problem.
The Boeing Co. reported that its 737 jetliners have experienced apparent rudder problems 187 times since 1970, putting new focus Thursday on the question of whether two unsolved 737 crashes are isolated incidents or symptomatic of a continuing problem with the world’s most widely used airliner.
The chairman of the National Transportation Safety Board also expressed concerns Thursday about Boeing’s failure to include two other rudder malfunction incidents in its report.
The rudder system remained the primary suspect as the NTSB completed its fourth day of hearings here on the crash of USAir Flight 427, a 737 jet that rolled to the left and plunged nose-first into a shallow gully as it was preparing to land at Pittsburgh International Airport last Sept. 8. All 132 aboard the plane were killed.
The cause of the crash remains a mystery, but several expert witnesses have said the rudder mechanism is the only control system on the plane that could have caused the jetliner to behave as it did.
The rudder--a hinged slab on the vertical tail that helps a plane turn right or left by pushing the tail in the opposite direction--is also a prime suspect in the 1991 crash in Colorado Springs, Colo., of United Airlines Flight 585, another Boeing 737.
NTSB investigators have never figured out what caused Flight 585 to crash, but they have determined that it, too, rolled to one side and plunged nose-first to the ground as it was preparing to land.
Boeing documents show that 737s suffered 187 “lateral or directional control upsets” apparently caused by rudder control system malfunctions between 1970 and 1995. In most cases, the 737’s yaw damper--an automated component that is supposed to cancel out the plane’s natural tendency to fishtail slightly--is the presumed culprit.
None of these upsets caused a major emergency or crash, but they did prompt the flight crews to make precautionary landings or file incident reports with Boeing.
Boeing Chief Engineer Jean McGrew acknowledged that the 187 incidents were a “large number.” But Boeing argued that no continuing problem exists, noting that in every case, the cockpit crew was able to recover and land safely. McGrew said new Boeing planes now on the drawing board will use essentially the same rudder systems, although minor modifications will be made to improve reliability.
The report of the 187 incidents was contained in a mound of paperwork submitted to the NTSB a few days before the hearing. The incidents are listed by date; the information is scanty, since each item is accorded less than a single typewritten line:
“2/2/72--Severe/violent rudder motion during climbout.”
“1/7/88--Rudder trim stuck, causing violent dive to the right.”
“7/26/93--At crz (cruise), . . . apl (airplane) yawed viciously.”
NTSB Chairman Jim Hall questioned McGrew sternly Thursday after learning that Air France had told investigators about two other non-emergency 737 rudder incidents that Boeing had omitted from its report.
“I am concerned over information from another party that we didn’t get from you,” Hall said. “I would like to be sure that all the facts and data are available (from Boeing) . . . to either rule in, or rule out, the rudder” in the crash of Flight 427.
Hall asked McGrew to assure him that Boeing would turn over all pertinent information.
“Mr. chairman, I will do that,” McGrew responded. “We’re holding back nothing from you. . . . I hope it is very clear that it is in Boeing’s best interests to find any faults” in the 737, McGrew added. He said the company needs “the confidence of the American public.”
McGrew later told reporters that the omission of the Air France incident was an oversight that occurred because those malfunctions--which did not require any corrective maintenance--were not included in the database from which the list was compiled.
He said the company would conduct a thorough search to assure that any data that might be considered pertinent to the investigation will be turned over to the NTSB.
Like several other Boeing engineers who testified earlier this week about what might have caused Flight 427 to crash, McGrew said the plane’s twist, roll and nose dive all make the rudder “the logical candidate.”
But--again echoing his cohorts--he said none of the parts recovered from the wreckage show any evidence that any of the rudder-control systems on that plane malfunctioned.