SAM WILLIAMS STOOD AT THE PODIUM AND EXPLAINED why he enjoyed his occupation. “One of the great things about invention is that your wife can’t tell whether you’re asleep or inventing,” he told the audience. “You can be sitting by the TV, having a couple of beers, and she never knows the difference.”

If Williams abused his ability to goof off while appearing to work, you can’t tell by looking at his career. He repeatedly created new, improved ways to make jet engines smaller, lighter, and more powerful. He made it possible to create a new generation of small business jets, as well as the miniature power plants that drive America’s long-range cruise missiles, which helped America’s endgame strategy in the final years of the Cold War.

During a private conversation I asked Williams if he thought aviation innovation had stalled. “Oh, no. I don’t think so at all,” he said. “There’s always the opportunity to use new materials, new designs, to create something better than what’s been done before.”

The occasion of Williams’s public comments was his induction into the National Inventors Hall of Fame. To mark the hundredth anniversary of Orville and Wilbur Wright’s first powered flight, in 1903, the Hall recognized 17 inventors in the field of aviation and aerospace. Collectively their achievements stand as a monumental tribute to the tradition of the Wrights.

The centennial also marks the end of an era. After 100 years of breathtaking advances in aviation and aerospace, it’s time to ask whether the pace of innovation has slowed, as often happens when a technology reaches maturity. As I write this column, Air France is completing the final flight of its Concorde supersonic transport. British Airways plans to mothball its Concorde fleet in October. It’s not just the end of champagne and caviar for the privileged few who could afford the experience of commercial flight at twice the speed of sound. The demise of the Concorde underscores the larger truth that the world’s airlines have gone an entire generation without progress on the goal to fly faster.

Late last year Boeing abandoned plans for an innovative sonic cruiser that would have cut flight times by 20 percent by flying just under the speed of sound. The plan was deemed technically feasible, and the aircraft itself featured a graceful design that would have made it one of the loveliest machines in the sky. Still, Boeing executives decided it was too risky to spend the money to develop such an innovative aircraft. Instead they (and the rest of the world’s commercial jet manufacturers) will continue to pursue incremental improvements to designs originating in the 1950s.

The state of aerospace is equally discouraging. Human space flight has been stuck in low orbit since the crew of Apollo 17 returned from the moon in 1972. The International Space Station is a dramatic technological achievement, but equally dramatic cost overruns are blamed for the cutbacks that restrict it to a skeleton crew that does almost no science. Their time is devoted almost entirely to handling routine maintenance. Tragically, the most significant aerospace event of this centennial year may be the final flight of the space shuttle Columbia . Experts are still investigating the exact sequence of events that caused the failure, but they all agree that a replacement for the aging shuttle fleet is long overdue.

It’s disturbingly easy to find examples of retrograde motion in aviation. A visit to any good aviation museum shows that a growing number of the historic aircraft on display represent technological pinnacles that won’t be bested any time soon. In the field of rocket planes, the reigning king is the 1959-vintage X-15. The high-flying, ultra-swift Lockheed SR-71 Blackbird is my personal nomination for the most advanced aircraft ever, and it first flew in 1964. In the field of rocketry the heavyweight champion remains the Saturn V, which made its debut in 1967. The most significant aviation records being set today may be the longevity achievements of the Air Force’s long-range B-52 bombers, piloted by men and women born long after the jets first flew, in 1952.

In fairness, it’s possible to find impressive examples of contemporary innovation in aviation. The war with Iraq featured smart ordnance fired from stealthy aircraft. Unmanned drones show great potential. Commercial aircraft may not fly faster or higher than in the past, but they make less noise and use less fuel.

I asked Richard Whitcomb, the aerodynamics genius, the same question I had posed to Williams. “If you want to make an impact or have an effect, don’t go into aeronautics. It’s pretty well stabilized,” he replied. “No big things have come up in aeronautics since my inventions.” (See my interview with him on page 60.)

My feeling is that both Williams and Whitcomb are right. It’s true that there’s still room for innovation in aviation. Excellent ideas emerge almost daily from top aircraft designers, from the military, and from NASA. But unfortunately, few of these ideas are ever built. Although innovation remains possible, the most practical aviation technologies became realities in these first 100 years. While there’s no shortage of people longing to commute to work in personal helicopters or book passage to Mars, most folks are satisfied to get discount fares to Cancun or occasional upgrades to first class.

As we look back at the century ending now—and forward to the century about to commence—we should recognize that the real achievement of the aviation inventors of the past was to deliver a fully formed technology so that future generations can deliver another.