More Death From Above
When a 300,000-pound jetliner loses its tail fin in the first moments after takeoff, it stops slicing straight through the air and instead begins to wobble. The wobble causes the plane to slow down, even if the engines remain at full thrust, and changes the wings' position relative to the airflow. One wing rises, as it has been designed to do ever since Bernoulli plumbed the secrets of flight; the other wing dips. The differential throws the plane into a hard bank that can degenerate into a corkscrew, with the fuselage diving nose first toward the ground. The pilots can no more save the plane and its passengers than a trader on the 102d floor of the World Trade Center can shoo away an incoming 767.
Comparisons with September 11 were inevitable last week, as death and destruction once again rained down from the skies onto New York. When American Airlines Flight 587 crashed as a result of just such a tail loss less than three minutes after taking off from Kennedy International Airport--the charred and mangled wreckage falling into the residential neighborhood of Belle Harbor in Queens --it seemed as if the agony of two months before had revisited itself on a still-grieving country, a still-shaken city. Belle Harbor is a neighborhood of firefighters and cops, and within seconds of the crash the streets and sidewalks had filled with off-duty civil servants, many of them reprising, on another clear and sunny morning, their actions of September 11. Nobody, as one fire lieutenant told reporters, "ran the opposite way." Yet with a jet engine smashing into a shed and sending a wall of fire into a house and burning metal igniting trees like torches, running away would have been understandable. Belle Harbor lost almost 100 people in the World Trade Center attacks, including 71 firefighters. Now backyards and streets were strewn with body parts. Five people on the ground were killed, and a neighborhood that had already borne the unthinkable was forced to bear it again.
Officials shut all area airports, closed tunnels and bridges, ramped up security at nearby nuclear power plants, locked down the United Nations, evacuated the Empire State Building, diverted dozens of New York-bound flights... and, item by item, kept working through the terrorism-response checklist that defines the new normal. But within hours it became clear that Flight 587 was likely felled by mechanical failure, not terrorism.
Initial hypotheses about the causes of a plane crash often miss their mark, and last week's were no exception. Early speculation centered on the engines, but both were found largely intact. In fact, the cockpit voice recorder indicated that the engines were working when the pilots began losing control of the plane. Flight 587 fell out of the sky because its tail assembly fell off the fuselage, landing in Jamaica Bay. The mystery is why.
What investigators from the National Transportation Safety Board (NTSB) know is that Flight 587, an Airbus A300, took off at 9:14 from runway 31-L at Kennedy with 251 passengers and nine crew members for the 3i-hour trip to Santo Domingo in the Dominican Republic. At 107 seconds, the cockpit audio recorder picked up a strange rattle, which investigators believe came from the structure of the plane. At 114 seconds, the co-pilot said the plane had just experienced a "wake encounter," in which it was buffeted by turbulence from the wingtips of the Boeing 747 in front of it. At 121 seconds, a second rattle sounded. At 125 seconds, a pilot called for "maximum power." And two seconds after that, a pilot indicated that he had lost control of the plane. The voice recording ends a few seconds before impact.
The flight data recorder cut out about 20 seconds before that, leaving investigators mystified about how the 27-foot-high tail assembly broke off. The two wakes that Flight 587 flew through, 20 seconds apart, were well within the tolerance for turbulence--one tenth of a G-force. More suspicious is that, in the eight seconds after the Airbus flew through the second wake, it jerked sideways with abnormal force: right, right again and then sharply left. Those turns corresponded to movements of the plane's rudder. After the three jolts, the plane began turning left 10 degrees per second, banking at a 25-degree angle with the left wing dipping. The nose pitched down 30 degrees, and everyone inside felt a force of two Gs--almost what you would feel in a stomach-dropping roller-coaster plunge. The pilots had turned the controls right, as if they were trying to yank the plane out of a death spiral. They couldn't.
Those jerky rudder movements might have produced sufficient aerodynamic forces to snap the tail assembly off the doomed plane, and so are the focus of the investigation. Analysis of the flight data recorder does not yet reveal whether the rudder movements followed commands from the cockpit. Rudder movement at the wrong time can exacerbate rather than correct sudden turbulence. Another possibility, however, is that the rudder movement was "uncommanded." In such a case the rudder, with no pilot input, can swing abruptly from side to side, making the plane difficult to control. The NTSB concluded that "uncommanded rudder deflection" downed a Boeing 737 near Pittsburgh in 1994, and though Boeing disagreed, it redesigned a small part that moves the rudder anyway. At least one Airbus also had a rudder problem. NTSB records show that on May 11, 1999, an Airbus A300 en route from Bogota to Miami experienced a series of what seemed to be uncommanded rudder movements. The American Airlines flight had to abort one landing while the pilot wrestled with the controls, and the deflections worsened as he came around for another try. The plane eventually landed safely. The chaotic rudder movements on Flight 587, whatever their source, might have provided sufficient lateral forces to snap off the tail. The data showing rudder position starts to disintegrate 2 1/2 seconds before the flight data recorder goes silent. This might have been when the tail assembly broke off.
For abnormal stresses to break off the tail, the assembly almost surely would have had to harbor a structural flaw. The tail is attached to the fuselage by six fittings protruding from the main tail section, three on each side. A metal bolt holds each fitting to a set of metal brackets atop the fuselage. These fittings, retrieved from the wreckage, remained attached to the metal frame: the tail assembly, in other words, did not separate at its attachment points. Instead, it split off sharply and cleanly at its base, something unknown in the history of commercial aviation.
That has the NTSB investigating the materials in the tail assembly, which is a so-called carbon composite. (The fittings that slip into the metal brackets are an integral part of the tail and therefore also composites.) This mix of carbon fibers and resins is lighter and more corrosion-resistant than aluminum and, pound for pound, stronger. But composites, as the name implies, are formed of a mix of materials. As such, they can "delaminate," in which the layers peel apart. (Just before Airbus delivered the plane to American in 1988, the composite material in the left center fitting that holds the tail assembly to the fuselage had started to delaminate; the manufacturer added additional layers of material as well as rivets.) Composites are also subject to "crazing," in which the resins flake away, revealing the carbon fibers. And composites can snap off at microscopic "score" lines, much as glass breaks where diamond scores it.
This Airbus was still too young (37,500 hours in flight, 12,000 takeoffs and landings), investigators say, to experience the structural failures of old age. It did, however, suffer severe turbulence on a 1994 flight from Barbados to Puerto Rico; 47 passengers and crew were injured. Investigators are probing whether that shake-up left structural damage. If so, it likely went undetected: regulators are so confident of the safety of composites that they require only that tail assemblies in the Airbus A300 be inspected visually, every five years. On this plane, the last such check came in December 1999. U.S. officials now acknowledge that visual inspection alone could probably not catch microscopic flaws. Two days after the crash, American Airlines began inspecting the tail assemblies on each of its 34 remaining A300s. And the FAA planned to order inspections--perhaps with ultrasound--of all A300s and A310s, a sister model.
There is endless talk about how September 11 changed America and Americans. Much of it has proved dead wrong: we do indeed still love escapist entertainment. But one change was on display before the fires from Flight 587 were even quenched: our perspective on death, disaster and tragedy has been profoundly altered. We witnessed the murder of some 4,400 people. After that, 260 accidental deaths affect us differently. When New York Mayor Rudy Giuliani said, in those first hours after the crash last week, "It could have been worse," he was referring not only to the death toll--that a jetliner slamming into a residential neighborhood killed only five people on the ground seemed miraculous--but to the apparent absence of terrorist involvement. Evil had seemingly not brought down Flight 587. And although countless Americans were appalled to catch themselves thinking, "Oh, OK, it's just a 'normal' fatal-to-hundreds plane crash," it seemed easier to accept the familiar tendency of machines to occasionally fail.
That was reflected in travel plans for Thanksgiving and beyond. Last week's crash caused barely a downtick in travel-agency airline bookings (though some passengers refused to fly an Airbus A300). Travel agent bookings fell 20 percent on the day of the crash compared with the week before, but were down only 10 percent on Thursday. "People are definitely nervous about air travel and more cautious, but those who booked for Thanksgiving are going ahead with their plans," says Oakland, Calif., travel agent Don Carter. That reflects in part the very different emotions triggered by accidents and terrorism. "If it's an accident, there's no reason to think it will happen more than in the past," says psychologist David Carbonell, director of the Anxiety Treatment Center in Chicago. "If it were terrorism, it would provide fresh evidence that they're good at this and are doing it again." As awful as any 265 deaths always are, it is easier to accept random failures than the idea that someone is out to kill you.
In a graphic that accompanied our Nov. 26 story about the crash of American Airlines Flight 587, "More Death From Above," we inadvertently failed to say that our source for the altitude data for the flight was Megadata PASSUR System.