Demand did soften in the months immediately following the ban, hitting the third-quarter results of airlines such as JetBlue Airways and Southwest Airlines .
But travel has mostly returned to normal as the TSA eased restrictions on liquids in September and people got used to the new procedures.
Each passenger may now carry liquids or gels in bottles no larger than 3 ounces, placed in one clear quart-sized plastic zip-top bag, the TSA says on its Web site. Medications, baby formula, breast milk and juice are allowed in larger quantities, but must be declared for inspection at the security checkpoint.
"Much like all of the various mandates from the TSA, the first month or two were chaos," said Doug Harkness, an engineer from Chicago who flies about once a week. "Once you get past that, things tend to be more normal."
Fact of Life
The Air Transport Association, a trade group representing major U.S. airlines, has seen little impact from the policy on day-to-day operations, said spokeswoman Elizabeth Machalek Merida.
At JetBlue, the amount of checked baggage increased by 20 percent immediately after the TSA directive, but is now back to pre-liquid ban levels, spokeswoman Alison Eshelman said.
As JetBlue and other airlines worked to educate their passengers about what could not be brought on planes, Eshelman said, savvy travelers learned to pack around the restrictions.
But Southwest, the U.S. No. 1 discount carrier, said it was still handling 23 percent more checked bags than before the TSA's restrictions. By scheduling more baggage handlers for shifts, the carrier has been able to cope with the new reality.
"Once we got used to (the increase), we were better able to plan," said spokeswoman Beth Harbin.
Although restrictions on liquids have become a fact of life for airlines and travelers, it's difficult to know if these measures are deterring attacks.
"The trouble with terrorism is it's not like safety," said Kenneth Button, a professor at George Mason University's School of Public Policy. "Safety is a technical problem."
If some part of an airplane is malfunctioning, it can be repaired, Button said, but averting terrorism is not that simple. "Every time you stop one attempt, they change tactics," he said.
Security measures such as the TSA's ban on liquids are partly cosmetic, according to Button. They keep travelers aware of dangers and encourage them to be vigilant, but they also serve to make people generally more confident about flying.
Since people are flying more than ever and there has not been a significant successful attack on airlines since Sept. 11, 2001, Button said regulators must be doing something right.
"Altogether security seems to be working," he said, "but which measures work and don't work, it's hard to tell."