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What made an Airbus rudder snap in mid-air?
13 March 2005
At 35 000 feet above the Caribbean, Air Transat flight 961 was heading home to Quebec with 270 passengers and crew. At 3.45pm last Sunday, the pilot noticed something very unusual. His Airbus A310's rudder -- a structure over 8m high -- had fallen off and tumbled into the sea. In the world of aviation, the shock waves have yet to subside.
Mercifully, the crew was able to turn the plane around, and by steering it with their wing and tail flaps managed to land at their point of departure in Varadero, Cuba, without loss of life. But as Canadian investigators try to discover what caused this near catastrophe, the specialist internet bulletin boards used by pilots, accident investigators and engineers are buzzing.
One former Airbus pilot, who now flies Boeings for a major United States airline, told The Observer: "This just isn't supposed to happen. No one I know has ever seen an airliner's rudder disintegrate like that. It raises worrying questions about the materials and build of the aircraft, and about its maintenance and inspection regime. We have to ask as things stand, would evidence of this type of deterioration ever be noticed before an incident like this in the air?"
He and his colleagues also believe that what happened may shed new light on a previous disaster. In November 2001, 265 people died when American Airlines flight 587, an Airbus A300 model which is almost identical to the A310, crashed shortly after take-off from JFK airport in New York. According to the official report into the crash, the immediate cause was the loss of the plane's rudder and tailfin, though this was blamed on an error by the pilots.
There have been other non-fatal incidents. One came in 2002 when a FedEx A300 freight pilot complained about strange "uncommanded inputs" -- rudder movements which the plane was making without his moving his control pedals. In FedEx's own test on the rudder on the ground, engineers claimed its "acuators" -- the hydraulic system which causes the rudder to move -- tore a large hole around its hinges, in exactly the spot where the rudders of both flight 961 and flight 587 parted company from the rest of the aircraft.
On Sunday night Ted Lopatkiewicz, spokesperson for the US National Transportation Safety Board (NTSB), which conducted the flight 587 investigation, said that the board was "closely monitoring" the Canadian inquiry for its possible bearing on the New York crash. "We need to know why the rudder separated from the aircraft before knowing whether maintenance is an issue," he added.
Airbus -- Europe's biggest manufacturing company, to which British factories contribute major components, including aircraft wings -- has now overtaken Boeing to command the biggest share of the global airliner market. In sales literature to operators, it described the A300 series as a "regional profit machine".
The firm recently launched its superjumbo, the two-storey A380, which is due in service next year. Like earlier Airbus models, this relies heavily on "composite" synthetic materials which are both lighter -- and, in theory, stronger -- than aluminium or steel. Fins, flaps and rudders are made of a similar composite on the A300 and A310, of which there are about 800 in service all over the world.
Composites are made of hundreds of layers of carbon fibre sheeting stuck together with epoxy resin. Each layer is only strong along the grain of the fibre. Aircraft engineers need to work out from which directions loads will come, then lay the sheets in a complex, criss-cross pattern. If they get this wrong, a big or unexpected load might cause a plane part to fail.
It is vital there are no kinks or folds as the layers are laid, and no gaps in their resin coating. Holes between the layers can rapidly cause extensive "delamination" and a loss of stiffness and strength.
Airbus, together with aviation authorities on both sides of the Atlantic, insists that any deterioration of a composite part can be detected by external, visual inspection, a regular feature of Airbus maintenance programmes, but other experts disagree.
In an article published after the flight 587 crash, Professor James Williams of the Massachusetts Institute of Technology, one of the world's leading authorities in this field, said that to rely on visual inspection was "a lamentably naive policy. It is analogous to assessing whether a woman has breast cancer by simply looking at her family portrait."
Williams and other scientists have stated that composite parts in any aircraft should be tested frequently by methods such as ultrasound, allowing engineers to "see" beneath their surface. His research suggests that repeated journeys to and from the sub-zero temperatures found at cruising altitude causes a build-up of condensation inside composites, and separation of the carbon fibre layers as this moisture freezes and thaws. According to Williams, "like a pothole in a roadway in winter, over time these gaps may grow".
Commenting on the vanishing rudder on flight 961, he pointed out that nothing was said about composite inspection in the NTSB's report on flight 587. This was an "unfortunate calamity", he said. Although the flight 961 rupture had yet be analysed, he continued to believe Airbus's maintenance rules were "inadequate", despite their official endorsement.
Barbara Crufts, an Airbus spokesperson, said visual inspections were "the normal procedure" and insisted Williams's case was unproven. "You quote him as an expert. But there are more experts within the manufacturers and the certification authorities who agree with these procedures." She disclosed that the aircraft used in flight 961 -- which entered service in 1991 -- had been inspected five days before the incident. She said did not know if the rudder had been examined.
Despite these and earlier assurances, some pilots remain sceptical. The Observer has learnt that after the 587 disaster, more than 20 American Airlines A300 pilots asked to be transferred to Boeings, although this meant months of retraining and loss of earnings. Some of those who contributed to pilots' bulletin boards last week expressed anger at the European manufacturer in vehement terms. One wrote that having attended an Airbus briefing about 587, he had refused to let any of his family take an A300 or A310 and had paid extra to take a circuitous route on holiday purely to avoid them: "That is how convinced I am that there are significant problems associated with these aircraft."
Another seasoned pilot with both military and civilian experience said: "Composite experts across the country advocate state-of-the-art, non-destructive testing to prevent this type of incident from happening, yet civil aviation authorities still only require 'naked eye' or other rudimentary inspections. How many more incidents have to occur for decision-makers to do the right thing by passengers and crews?"
He said that while flight 961 had come down safely, to land a plane without a rudder in a crosswind or turbulence could be impossible. The rudder was all the more important on a plane such as an A310, because its wing design meant that it was "aerodynamically unstable" and needed the rudder for stability.
Air Transat, a charter operator which flies from Canada to Europe and the Caribbean, said that after the incident it "immediately carried out a thorough visual examination of all its Airbus A310s... and no anomaly was detected."
The separation of the rudder may have further implications for the cause of the 587 crash. In its report, the NTSB said the tail and rudder failed because they were subjected to stresses "beyond ultimate load", imposed because the co-pilot, Sten Molin, overreacted to minor turbulence and made five violent side-to-side "rudder reversals". The report said the design of the A300 controls was flawed because it allowed this to happen.
However, the NTSB investigation has been criticised by many insiders. Ellen Connors, the NTSB chair, told reporters last January that the report was delayed because of "inappropriate" and "intense" lobbying by Airbus over its contents, adding: "The potential for contaminating the investigation exists." In America, the NTSB staff is small and manufacturers provide many of the staff employed on air-crash investigations into their own products.
Dozens of former accident investigators, engineers and pilots, including some who were involved in the official inquiry but were disappointed by its conduct, poured their expertise into a parallel investigation run by Victor Trombettas, who lives near the crash site and runs a website, usread.com. Drawing on the huge mass of technical data released after the crash, they question the conclusion that "aggressive" rudder inputs were the crash's main cause.
"I don't think the NTSB did a quality job," said Vernon Grose, a Washington safety consultant who is a former board member. He supported the conclusion of Trombettas's group -- that more than ten seconds before any rudder movements, the 587 pilots were fighting to regain control of the aircraft for reasons that remain unknown: a still-to-be investigated technical failure, or possibly a terrorist bomb. The crash, he recalled, took place two months after 9/11. Ninety per cent of the witnesses who saw the plane from the ground said they saw smoke or fire billowing from it before the tail and rudder fell off, Grose said.
"RickUSN-
That was intelligent and useful Mudd.
But it certainly is what Ive come to expect.
Mindless babbling with no intent to either enlighten or inform.
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