A huge program with the FAA will replace a hydraulic valve that was the suspected culprit in two fatal crashes of the world's most widely used airliner.
Boeing and the Federal Aviation Administration will undertake a massive redesign of the rudder system of the Boeing 737, the world's most widely used jetliner.
The company and the FAA soon will announce plans to replace a controversial hydraulic valve in all 3,200 737s now in service. The announcement could come as early as today.
The 737 "is going to be around for a long time," FAA spokeswoman Diane Spitaliere said. "We feel like this is a long-term solution."
The giant retrofit program, scheduled to take place over the next five to seven years, will eliminate the unusual valve that was the suspected culprit in the crashes of USAir Flight 427 near Pittsburgh in 1994 and United Airlines Flight 585 in Colorado Springs, Colo., in 1991. The National Transportation Safety Board said those crashes "most likely" were caused by a valve jam that made the rudder move the opposite direction from the pilot's command.
Boeing plans to pay for the full cost of the retrofit, estimated to be about $240-million. The work will be done during regularly scheduled maintenance for the 3,200 737s around the world, so there should be no serious disruption in airline schedules.
FAA officials say the plane has an excellent safety record and steps have been taken to train crews to deal with rudder problems. They say there is no immediate need to ground the fleet.
The announcement marks a dramatic change for Boeing and the FAA, which staunchly opposed a redesign for several years. Their joint announcement is prompted by an upcoming report from an FAA engineering panel that will call for a redesign of the rudder system. The panel was set up last year at the suggestion of the NTSB to take an impartial look at the 737's rudder system.
The panel, known as the Flight Control Engineering and Test Evaluation Board, identified new possible failures in the existing system, including some that could cause the rudder to suddenly deflect fully to one side, which would make the plane difficult to control.
The rudder is the movable vertical panel on the tail that points the plane's nose right or left. The plane's hydraulic system provides the muscle for the rudder, using fluid under extreme pressure. The valve is the key device in the system, controlling fluid that pushes the rudder right or left.
Ever since the Pittsburgh crash, which killed all 132 people on board, NTSB investigators have said they were concerned about the reliability of the rudder valve. Its unique "valve-within-a-valve" design was supposed to provide a backup in case one should fail, but investigators found the design created potentially serious problems because pilots might be unaware of a jam. NTSB officials complained that the valve was not "reliably redundant" and said it wouldn't meet current safety standards.
Last summer's NTSB report on the USAir crash said that despite many improvements in the past five years, "the 737 series airplanes remain susceptible to rudder system malfunctions that could be catastrophic."
Boeing and the FAA have insisted that the valve was safe.
Over the past five years, they agreed to many fixes, including one that prevents the valve from pushing the rudder the wrong direction and another one that prevents the rudder from suddenly moving to full deflection. But officials opposed a complete overhaul of the rudder system because they said there was no proof that the valve caused the crashes. There were no scratches to indicate a jam and no conclusive evidence on the cockpit tape that the pilots thought they had a malfunction.
Boeing officials blamed the pilots for the USAir crash. Boeing said the USAir co-pilot had been startled and mistakenly stomped on the left rudder pedal.
For their part, FAA officials have said their rudder fixes in the past few years have solved any potential problem with the 737 fleet. The FAA required more training for pilots to recover from rudder mishaps and had Boeing fix a trouble-prone device called a yaw damper coupler.
But questions have lingered about whether the government and Boeing had truly fixed the problem. A strange rudder incident involving a MetroJet 737 over Maryland in February 1999 just deepened the mystery. Many 737 pilots have continued to believe there was a "gremlin" in the valve that had not been found.
Now, Boeing and the FAA have agreed to make changes.
The pilot procedure for handling a jammed rudder is being simplified. Instead of the current one, which involves a complicated list of conditions, pilots next month will receive a new procedure that can be memorized more easily.
"We've come up with a new procedure that is a lot simpler," said the FAA's Spitaliere. "You don't have to be dragging out manuals."
The 737's new rudder system will be similar to the one on the 757 and 767 fleet. It will have two separate valves that will enable pilots to break out of a jam by stomping hard on a rudder pedal _ something they cannot do on the current 737 system.
A third valve will act in concert with those valves to provide a backup.
The current system
A valve-within-a-valve. If one valve jams, the other should still operate. But the unique design was controversial. The NTSB said pilots might be unaware of a jam with one valve.
The new system
Two separate valves, similar to Boeing 757 and 767. It's a simpler, more widely used system that should alert pilots when there is a jam.
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