***^***^***^*** Flight 587 ***^***^***^***
Like many of my generation, I recall where I was and what I was doing when I heard the news of the assassinations of JFK, MLK, and RFK. But unlike many of my generation, I also recall where I was and what I was doing when I heard the news from Orly, France in March 1974; Tenerife, Spain in March 1977; Chicago in May 1979; Mount Otsuka, Japan in August 1985; Lockerbie, UK in December 1988; New York in July 1996: all major crashes of commercial airlines.
On 12 November 2001, as I worked in front of my muted television that was tuned to a cable news channel, I witnessed some of the earliest broadcasts of the crash of American Airlines Flight 587, an Airbus Industrie's A300-600, in the Queens neighborhood of Belle Harbor, about 103 seconds after takeoff from JFK International Airport. All 251 passengers and a crew of 9 aboard, as well as 5 people on the ground, were killed.
Much of the intervening investigation of the accident has focused on the aircraft's vertical stabilizer, a state-of-the-art, approximately 28-foot-tall, complex structure that has been implicated in the crash. The vertical stabilizer on Flight 587 snapped off ---a unique occurrence in modern commercial aviation--- and landed in Jamaica Bay, away from the fuselage crash site.
For the past thirty years, the bulk of my research career has been dedicated to the mechanics, design, fabrication, and nondestructive evaluation (NDE) of nonmetallic fiber reinforced composite materials ---the same type of materials from which the Airbus A300-600 vertical stabilizer is made. I have thought about Flight 587 every day since November 12th.
In essence, Airbus's NDE policy for its A300-600 composite vertical stabilizer is that damage that cannot be seen with the unaided eye will not compromise its structural integrity. This is a lamentably naive policy. It is analogous to assessing whether a woman has breast cancer by simply looking at her family portrait.
Although Airbus has attempted to defend its NDE policy, the vertical stabilizer on, at least, one other A300-600, which displayed no damage to the unaided eye, upon closer inspection contained a significant structural flaw. Intransigently, Airbus has stated that, even with such damage, the aircraft was safe to fly.
The Federal Aviation Administration (FAA), in conjunction with the National Transportation Safety Board (NTSB), appears to be moving toward a more rational NDE policy that would ground all A300-600s that experience lateral (that is, side-to-side) forces exceeding 35% of the force of gravity. Lesser requirements would be imposed on aircraft experiencing lesser, though high, lateral forces. Airbus's input would be sought regarding subsequent inspection of each such aircraft, though I believe Airbus's potential advice has been compromised by its dubious policies.
Dozens of American Airlines A300-600 pilots feel they have been stonewalled in their requests for strong corporate and regulatory actions, and although they believe the inspection policies for this aircraft are inadequate, they continue to fly, as the investigation proceeds at an uncomfortably sluggish pace. Although the NTSB and the FAA have been slow in this investigation, it is my hope that, with NASA's technical support, they will ultimately fulfill their missions concerning Flight 587. Even so, that would be just the beginning!
There are several unvoiced issues that remain; two of which are the aging and the repair of nonmetallic fiber reinforced composites.
By aging, I mean the deterioration that occurs during long-term in-service mechanical and environmental loading, in the absence of an overloading or catastrophic event. When subjected to the loading histories of some aircraft, composites will lose both strength and stiffness. Furthermore, studies of the long-term effects of exposure to aircraft environments of moisture, pressure and temperature, as well as fuels, hydraulic fluids, lubricants and deicers remain to be conducted for many composite materials. Since such deterioration may be monitored nondestructively, this is another rationale for long-term NDE monitoring.
Reportedly, the vertical stabilizer on Flight 587 had been repaired with metal rivets and additional materials. Such repairs of structural damage in composites are frequently unreliable, especially for joints and attachments involving primary (load-bearing) structures. The rupture of the vertical stabilizer on Flight 587 occurred in the vicinity of repairs, adjacent to an attachment point. Therefore, the FAA must carefully establish and articulate a policy for the repair of primary composite structures.
Finally, Airbus's extensive design and testing programs for the A300-600 composite vertical stabilizer may be currently deficient if they were based on outmoded or flawed engineering assumptions or an inadequate certification process. No amount of analysis can overcome faulty assumptions or insufficient requirements.
The specific cause(s) of the crash of Flight 587 remains uncertain; uncommanded rudder inputs, wake turbulence, and structural failure ---perhaps in combination--- are the prime candidates. There are several issues that are not under contention concerning primary composite aircraft structures, however, and paramount among these are the requirements for more effective implementation of their NDE and a better understanding of their aging and repair. With thousands of commercial aircraft containing structures made of composite materials, the safety and comfort of our families, friends, and the dedicated crews who serve us demand that these issues be addressed. And, out of respect for those directly affected by Flight 587, the sooner the better.
James H. Williams, Jr. is the School of Engineering Professor of Teaching Excellence, Charles F. Hopewell Faculty Fellow, and Professor of Writing and Humanistic Studies at MIT. In the early 1970s, he founded the Composite Materials and Nondestructive Evaluation Laboratory in MIT's Mechanical Engineering Department. Some of his other writing may be accessed via his home page: http://web.mit.edu/jhwill/www/