Absent 9/11, the entire United States would be a vastly different place. Dozens of laws, two decade-long wars, and thousands of deaths would never have come to pass. An entire industry based on fear a paranoia of terr'ist attacks would not exist. A full paradigm shift of a large part of the federal government from defence and/or criminal investigation to anti-terr'ism and "intelligence" operations would not have occured.

All of this would have affected our daily lives, not just air travel.

DHS wouldn't exist. TSA wouldn't exist. The Patriot Act would never have been passed.

Hijacking would still be in actual terrorists' toolboxes, because we wouldn't have hardened cockpit doors, and passengers would still go with the "do whatever they say and they won't hurt us" response, as opposed to the "OMG THEY'RE GONNA CRASH THE PLANE WE GOTTA KILL 'EM FIRST!!!" mentality that currently pervades.

The travel industry would still have gone into a slump in the early 2000's, but not to the extent that it did after 9/11. Someone, somewhere, would still have come up with the idea of fees - luggage fees, seat fees, pillow fees, etc.

Security would still be handled by the airlines, but at some point each airline would start assessing its own security fee to recoup those costs, similar to the government mandated 9/11 security fee we have today. The difference would be that, for several years, the fee would be wildly variable and completely unpredictable, until some advocacy groups convinced Congress to pass a law capping the fee (after which every airline would charge the maximum).

With security being handled by the airlines, no airline would ever have invested in NoS technology. And without the stink of fear permeating every fibre of the American soul, no rational American would ever have even considered allowing their children, spouses, or themselves to be oggled by a perv in a box, irradiated by BSX, or fondled by security goons.

There would probably have been a shift in rules over the years - nothing remains static for long - but airside would not be limited to ticketed pax only, which means that airside businesses would be doing better, and all of the new terminals, expansions, and remodels that have been constructed since 2001 would have much more extensive airside facilities, catering to not only pax, but see-er-off-ers and pick-er-up-ers as well.

Limited to the old-style WTMD and HHMD, security c/ps would be smaller and quicker. No TDC, no NoS, no ETD, far smaller baggage search tables, no penalty boxes. Since airlines would be paying for it all, and the amount they could recoup would be capped, they'd be interested in efficiency. Instead of carts, we'd see the rail system that's used in other countries for returning plastic bins to the beginning of the line. Instead of exit guards, there would be simple metal turnstiles.

Carry-on x-rays would be done differently; perhaps there would be two operators per line to give higher speed and redundancy, and software similar to the current ATR might be in use as a backup. Inside the tunnel, there would be ETD puffers, giving every carry-on a non-invasive sniff for explosives.

Since checked bags could be locked and secured, pilferage would be far less of a problem.

Photography wouldn't be a dirty word or a suspicious activity in airports. Local LEOs would not hassle anyone with a camera (except when someone snapped a pic of the LEOs themselves).

Ironically, one thing that would be very similar - the private security officers employed by the airlines would still be wearing rent-a-cop uniforms and badges.

And one thing that would be even worse than today - some of those private security guards could be ARMED, since they're essentially private security guards and can be certified as armed guards under the laws of the various states in which they operate. There would be no police powers issues or restrictions; they'd be armed private guards, just like the armed private guards you see in banks, convenience stores, and check-cashing places all over the US.

Protesters, activists, charity workers, religious proselytizers, picnicing families, and panhandlers, along with the inevitable pick-pockets and baggage theives, would still have airside access. Theft at the c/p would still be a problem, as theives could make off with your iPad or other loose items into the airside spaces much quicker and easier, because their shoes and belts would still be on.

But given the propensities for both automation and public area surveilance that we see today, I believe that security cameras would be much better. With the airlines in charge of security rather than the federal government, camera coverage would be much more complete and overlapping, equipment would be more reliable and better maintained, and each airport (at least the big ones) would have its own surveilance office, much like Vegas casinos, for the sole purpose of reducing the airlines' liability in case of a crime or passenger injury. After all, a few hundred thousand for gear, maintenance, and training per year can save millions in lawsuits.

Ah, if only to live in a world devoid of both TSA and DHS. What a world, what a world...