Until now, passenger convenience has largely been ignored. After 9/11, a litany of sharp objects was banned from carry-ons. After Richard Reid tried to ignite explosives hidden in his sneaker on a flight from Paris to Miami in Dec. 2001, travelers were told to remove their shoes for screening. And after British officials foiled a plot to blow up planes with liquid explosives in August 2006, liquids, gels and aerosols were banned, though later allowed as long as they were packed in tiny bottles and in plastic bags.

And just when passengers think they know the routine, the Transportation Safety Administration adds a twist. Earlier this month, for example, it began screening certain powders in carry-on luggage. And screeners recently started asking passengers to place shoes directly on conveyor belts rather than in bins, giving officers a better view of shoes as they come through.

It’s hard not to ask: Is all this necessary? Is it making us any safer? And will it ever get better? Based on interviews with a range of security experts, the answers increasingly seem to be no; not really; and not for a while.

Giovanni Bisignani, the chief executive of the International Air Transport Association, urged the Obama administration to deliver broad policy changes in security in a speech delivered to airline leaders in February.

“I am not convinced that we are much wiser or any more efficient with many of our processes,” Mr. Bisignani said. “As travelers, our shared experience is hassle, and as industry players, it is bureaucracy and cost. It is time for both to change.”

Of course, if we look back at the state of security before 9/11, it’s clear that we have made progress. People without a ticket can no longer waltz through the airport and up to the gate. Technology, including explosive-detection devices, has gotten better and is more consistently applied to checked and carry-on bags alike. Passengers are more consistently screened by a more stable security work force with less employment turnover. And at times, even the lines seem to be moving a hair faster.

A case could also be made that because there have been no successful attacks against a United States commercial flight since 9/11, the system is indeed working. But inconsistencies, contradictory rules and flat out screening failures continue to provoke skepticism among passengers and security experts alike.