Rudder Problems Likely Caused Long-Unsolved Plane Crash, NTSB Says
The mysterious crash of a Boeing 737 jetliner in Colorado 10 years ago probably was caused by rudder problems similar to those that brought down another 737 near Pittsburgh about four years later, federal officials finally concluded Tuesday.
In both cases, the pilots pushed pedals to move the rudder in one direction, but the rudder moved in the opposite direction, the National Transportation Safety Board said.
The rudder is the large, hinged slab on the vertical part of the tail that works like the rudder on a boat, helping a plane fly straight, turn right or turn left. Full deflection of the rudder can cause a plane to roll and then plunge.
In both crashes, the jetliners banked steeply to one side as they were preparing to land and then slammed nose-first into the ground. All 25 on board United Airlines’ Flight 585 died in the Colorado Springs accident on March 3, 1991. All 132 on USAir’s Flight 427 were killed in the accident near Pittsburgh on Sept. 8, 1994.
Since the two crashes, Boeing has redesigned and refitted the power control units for the rudders on all 737s flown in this country.
In its initial report on the Colorado Springs crash, issued in December 1992, the NTSB said it was not sure what went wrong.
However, investigators said that “the two most likely explanations” were an unusually severe atmospheric disturbance that went otherwise undetected and some sort of breakdown in the plane’s control systems--most probably the rudder system.
It was only the fourth time in their then-27-year history that the nation’s crash detectives had admitted defeat.
The three others are the crash of a Convair 440 in Bradford, Pa., on Jan. 6, 1969, that killed 11; the crash of a DC-9 in Huntington, W.Va., on Nov. 14, 1970, that killed 75, including the Marshall University football team; and the crash of a Convair 340/440 in Bishop, Calif., on March 13, 1974, that killed 36, including a film crew. Those cases are still unsolved.
When the USAir jetliner crashed near Alquippa, Pa., in 1994, readings from the flight data recorder recovered from the wreckage led quickly to suspicions that rudder problems might be the culprit.
The recorder’s data were programmed into a 737 cockpit simulator to study how the plane behaved during its last moments of flight.
Then, on June 6, 1996, an Eastwind Airlines 737 landed safely at Richmond, Va., after control problems on final approach to the airport.
Based on the data studies from the accident at Alquippa and the subsequent problems at Richmond, the NTSB concluded on March 24, 1999, that rudder reversal triggered by jamming in the main rudder power control unit probably caused the USAir crash.
Further studies led to Tuesday’s finding that the same thing happened in Colorado Springs.
The NTSB noted that, because the United jetliner started to roll fewer than 1,000 feet above the ground, the pilots could not have been expected to react in time to prevent the crash.
