Rudder could be cause of Air France crash, pilots and experts say

By Alexandra Marks

Christian Science Monitor

June 18, 2009

As they work to unravel the mystery of Air France Flight 447, aviation analysts and pilots are now urging investigators to focus attention on the plane's tail fin, known as the vertical stabilizer, in addition to the design of the Airbus's computerized flight controls.

The vertical stabilizer is one of the largest intact pieces of the plane recovered so far, and the Times of London reported this week that "one of the 24 automatic messages sent from the plane minutes before it disappeared pointed to a problem in the 'rudder limiter,' a mechanism that limits how far the plane's rudder can move."

Aviation analysts note that several Airbus 300 series jets have had tail fin and rudder problems in the past. (The rudder is the flight control on the vertical stabilizer, or tail fin.)

The most recent incident was in 2005, when the rudder suddenly ripped off the stabilizer of an Airbus 310 flying at 35,000 feet from Cuba to Quebec, Canada. That plane managed to land safely.

The most deadly event was the 2001 crash of American Airlines Flight 587, in which 265 people died when the plane's vertical stabilizer tore off soon after takeoff. Investigators blamed that crash on "over use" of the rudder pedal by the co-pilot. But critics note that just prior to take off, that plane also had problems with a computer tied to the rudder. That computer was reset by a technician prior to takeoff.

In light of the circumstances surrounding the loss of AF447, some analysts and pilots are now calling for the National Transportation Safety Board (NTSB) to reopen the investigation of AA587 in light of potential similarities between the two crashes. They're also calling for a thorough review of all past vertical stabilizer, rudder, and computer incidents on Airbus planes.

"Absolutely the NTSB should reopen the investigation," says Lee Gaillard, an aviation analyst in Saranac Lake, N.Y. "Given the implications that seem to be surfacing in this Air France crash involving the rudder and potential computer problems, the whole [Airbus] computerized system needs to be taken a very close look at."

French investigators Wednesday said they're now developing "an image that is progressively less fuzzy" about what happened that stormy night June 1 over the Atlantic Ocean, when Flight 447 disappeared.

Judging from the wreckage and bodies recovered so far, and the few clues sent electronically in the last four minutes of the flight, investigators believe the Airbus 330-200 jet probably broke apart in flight, then scattered over several miles.

"We are in a situation that is a bit more favorable than the first days," Paul-Louis Arslanian, head of the French civil aviation safety agency told reporters at a press conference in Paris on Wednesday. "We can say there is a little less uncertainty, so there is a little more optimism ... [but] it is premature for the time being to say what happened."

He cautioned that the search is continuing for the flight data recorders, which could hold critical clues as to what happened.

Investigators so far have focused on the potential that speed sensors, called Pitot tubes, could have iced up and provided faulty information to the flight control computers. In the past week, Air France has replaced the Pitot tubes on all of its Airbus 330s.

That theory was gleaned from the burst of automated messages about mechanical events sent during the last four minutes of the flight. Most of the messages appear to be linked to "incoherent" speed readings, which then affected other systems of the plane, Mr. Arslanian said.

But the report that one of those automated messages also indicated problems with the rudder limiter has renewed concerns first made public during the AA587 crash investigation in 2001.

At the time, a group of American Airlines pilots presented to the NTSB a 68-page dossier documenting incidences of uncommanded rudder movements in the A300 series jets.

The NTSB eventually concluded the cause of the crash was not a computer problem, but the co-pilot over-using the rudder pedal during some wake turbulence.

The animation in this NTSB simulation shows the pilots pushing the rudder pedals abruptly and sharply to the floor, which is what investigators believed caused the plane to lose its vertical stabilizer and crash.

But some pilots familiar with the A300 series jets still doubt that conclusion. They say that it would be physically very difficult for a pilot to make the kind of abrupt rudder pedal movements indicated in the simulation, particularly while going 250 knots, which the NTSB indicated was the plane's speed at the time.

"I just don't see the co-pilot making the kind of abrupt movement at that speed," says an A330 pilot with more than 20 years experience in military and

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