Some things are more enduring than others.
In 1969, Americans were listening to the music of the 5th Dimension. Major League Baseball's All-Star game was played in Washington, D.C., home of the Washington Senators. Richard M. Nixon began his star-crossed presidency.
And at McDonnell Douglas Aircraft Corp., a DC-9 twinjet that eventually would be designated No. 904 rolled off the assembly line to be claimed by Delta Airlines.
The culture of the late '60s is gone, but until Saturday afternoon, No. 904 was still plying the skies. Abandoned by Delta, the DC-9 was refurbished and resold to ValuJet, one of the low-cost airlines that have joined the nation's flight line in the ongoing process of shakeout and restructuring of the industry.
The plane's crash into the muck of the Everglades with the loss of all 109 aboard raises new doubts about an old issue: whether it is safe to fly passengers in planes subjected to 20 or 30 years of the stresses and strains of nearly constant operation. An unsatisfactory answer recurs: Nobody really knows.
"There is no inherent reason that an older aircraft can't fly as safely as a newer airplane, but that assumes proper crew training and discipline and regular maintainance and upgrades of vital systems," said Mike Overly of the Aviation Safety Institute, a non-profit watchdog group based in Worthington, Ohio.
"If all that happens, the older planes and the airlines that fly them are perfectly safe."
What is clear is that operating aging aircraft is a double-edge sword.
Like used cars, these planes are cheaper to buy but sometimes more expensive to maintain, a good-news/bad-news scenario for no-frills airlines trying to slash costs.
Budget carriers such as ValuJet operate under the same federal aviation regulations as major carriers such as United and Delta, and their aircraft must meet the same inspection and performance standards.
Nonetheless, the Federal Aviation Administration has recognized that an aging fleet requires special attention. It has developed new standards to detect and respond to structural fatigue cracking and corrosion, two of the most common problems with older aircraft. They are defects the full extent of which sometimes cannot be detected in a standard inspection process.
FAA records clearly show that in sheer numbers, the accident rate for budget carriers, those most likely to operate older aircraft, is lower than for larger airlines. In fact, the granddaddy of all no-frills airlines, Southwest, has never had a fatal accident.
But this can be misleading. There are more major carriers operating many more aircraft, increasing the statistical odds of an accident.
"It isn't fair to compare accident rates, really not fair at all, but that's the only tool we have right now," said Shelly Hazle of the National Transportation Safety Board in Washington, D.C. "There was one case where a ground crew member walked into a propeller. That's officially classified as an accident, but does it mean you shouldn't fly that airline? Probably not."
More appropriate would be a comparison of accidents per thousand air miles or hours flown, Hazle said. But, she added, the NTSB doesn't have that breakdown.
It also would be helpful if the FAA did a better job of tracking aircraft problems less serious than full-blown accidents. But the agency's program for reporting what are termed "incidents" _ landing gear malfunctions that don't result in accidents, for example, or faulty warning signals _ is haphazard at best. This makes it more difficult to spot trends, both for aircraft types and specific airlines.
If requirements for incident reporting were more strictly enforced, a reform for which the Aviation Safety Institute has campaigned, the safety profile of the budget airlines might look less optimistic, Overly said.
Some experts say that choosing an airline based in the United States, which has some of the most rigorous safety standards for aircraft and airports in the world, is about the only thing fliers can do to increase the odds in their favor.
dder was used in this report.