The U.S. government agencies with border search authority, especially ICE and CBP, claim the power to search both people who are arriving and departing the U.S. under that authority. They've decided to exercise this power much more regularly for arriving travelers than for departing travelers, in particular by physically making everyone pass through a CBP immigration and customs control checkpoint when they arrive in the U.S.

But they claim the power to do exactly the same kinds of examinations for people who are leaving the country; they just do this so rarely that they haven't built physical facilities to interview or search departing travelers on a large scale.

My impression is that they believe this authority commences when you begin the process of leaving the country, probably by checking in for your international flight. I don't know how that would work if you have a domestic connection prior to the international departure (if they would think they could perform a border search in the first airport or only in the second airport). Yes, that does mean that a CBP or ICE agent could come find you at the TSA checkpoint or, more likely, in the departure area or at your boarding gate and search or question you. This is true even if there are other passengers in the same terminal who aren't traveling internationally; whether the passengers are treated as subject to the border search authority could depend on where they're individually going, not just what physical part of the airport they're in.

I've never heard of this happening, but the agencies have policies for doing it.

Yes.

There are pilot programs at land borders requiring US citizens to submit to exit interviews and obtain permission to leave the country East Berlin-style. Searches on departure are being stepped up every year.

Recently in Atlanta the border cops were stopping everyone in the jetway boarding my international flight for an exit interview and search. They appeared to be looking for money and drugs and asked all of us in plain view to account for exactly how much cash we were carrying before we could be allowed to board. Since the place I was going and Atlanta are both known for petty robbery, I obviously didn't want to answer; the amount I was carrying was under the legal limit but enough to be worth stealing. The border cop was obviously annoyed and insisted on me saying the amount in front of everyone.

As long as police agency budgets shoot skyward and Americans are happy to submit to authorities, the sky's the limit.

There are procedures whereby I can be put in jail, removing my permission to leave the room where I've been forcibly relocated. But that doesn't mean I have to "obtain permission to leave the room" right now.

The no-fly list is utterly reprehensible, but it doesn't match what was said.

The CBP is cooperating with Canada to exchange information at border posts in real time about whom to permit to enter or leave over land borders and pressuring Mexico to join. Tracking is already in place. Secret prohibition on leaving by air is already in place for selected persons.

The U.S. government seems to generally support UDHR article 13(2) ("Everyone has the right to leave any country, including his own, and to return to his country") and ICCPR article 12(2) ("Everyone shall be free to leave any country, including his own"). The no-fly list definitely can be a serious problem for this, although people on it often can leave by boat or overland -- though they might have trouble getting the money or necessary visas to do so.

Also, some incidents of investigating and attempting to deport overstays who were deeply integrated into communities and clearly doing super-productive things have led to bad PR for immigration authorities, which could be another reason those authorities are incentivized not to get too good at it (though influenced by factors like what part of the country, where the people have migrated from, what their socioeconomic status is, and others).

On December 5, 2012, working with a LAX duty agent and Customs and Border Protection officers, Special Agent Hamako conducted the planned search of Kim as he departed the country. First, he searched Kim’s checked luggage, which was located behind the check-in counter with Korean Airlines. [...]

Next, Special Agent Hamako stopped Kim on the jetway between the gate and the airplane as Kim was boarding his flight. He identified himself and asked Kim if he had any electronics, to which Kim responded that he had a laptop. Special Agent Hamako told Kim that he would be detaining the laptop pursuant to a border search and that he would return it once the search was complete.

(from https://ecf.dcd.uscourts.gov/cgi-bin/show_public_doc?2013cr0...)

There are usually no checks when you leave the country, but they do happen sometimes. Once when I flew out of Philadelphia, there were people at the jetway wearing some kind of uniforms, who asked to see everybody's passports. No idea what they were looking for.

Is LAX different?

But it's not at all the way things work in US airports with international service.

The U.S. doesn't offer this, seemingly as a matter of policy, something which really annoys international travelers -- it's one of the most-complained-about U.S. policies on sites like FlyerTalk, even by U.S. citizens (because you can easily spend 1-2 hours clearing immigration, customs, and security for an international flight connection in the U.S. even if you didn't intend to visit the U.S. at all).

But as a result, almost all U.S. airports have some departing international and domestic passengers in the same terminal at the same time, or potentially allow both international and domestic departures from any terminal.

I think the specific option at LAX was post-2001, but you had to be on a specific pair of flights to take advantage of it. (I didn't do it, I just read about it on FlyerTalk and forgot the details.)

Yesterday I had a purely-domestic itinerary out of Philadelphia -- which is an international hub for US Airways/American Airlines -- and while waiting on my flight I wandered in and out of the international terminal several times without facing any additional security (I like watching the larger planes come and go, and the lounge in that terminal is nicer).

Which is the standard way international airports work in the US. There is no concept of "once you cross this point, you have to clear customs again to exit the terminal" here.

Not casting doubt on what you say, I just haven't seen this myself. I've never flown internationally out of LAX. Only domestically once, and I hope it will be my last!