"Random" does not mean there can't be a pattern or there isn't a chance of having the clumping you described. The most common misunderstanding of randomness forgets that each trial is independent - meaning that having the person in front of you selected has absolutely no effect on your chances of being selected yourself, and your outcome has no effect on the pax behind you.

Statistically speaking, there is a 0.39% chance of flipping a fair coin and getting "heads" 8 times in a row. (Equivalent to each person having exactly a 50% chance of being selected AND having 8 pax in a row selected.)

The chance of rolling a fair 10-sided die - 0 to 9 - and rolling 8 times without rolling a zero is 43%. (Equivalent to each person having a 90% chance of being selected AND having 8 pax in a row selected.)

Both hypotheticals include the "fair" qualifier, meaning that the assumption is true randomness without bias.

Practically speaking, either you witnessed a rare (but fully random) situation where the chances of each individual pax being selected was low OR they jacked up the chances of being selected. (Or both, which is the most likely situation at play.)

The big gotcha here is that it is the WTMD is used for selection, so presumably they are using a good pseudorandom stream that is seeded properly. The alternative (having a person stand at the WTMD and select pax "at random") is nearly guaranteed to be heavily biased and nowhere close to being consistent with the binomial distribution.

This seems to be bringing it in line with the British policy for scanner usage... a good next step would be to remove primary NOS like in Britain, and a better one would be to chuck the MMWs in the trash like Ireland did a few years ago because they were backing up the lines.

Somebody had to play quickie catch-up to meet their quota before end of shift.

Old thread, but I thought I'd share my experience this year. I haven't taken perfect stats, but I would guesstimate very conservatively that I have been "randomly" selected for secondary screening about 50+ times out of roughly 100 tries. What then happens is mostly dependent on the airport. At EWR they started the year requiring hand swabs and have since mived to NOS mandatory upon random beep. At AUS, hand swab has been customary but today I received a quick patdown instead.

But main thing to know is that I doubt there is anything random about these secondary screenings.

I'm guessing that it changes day to day.

They have their "Playbook" with different types of secondary inspections they can use.

I do not know who decides the frequency of random beeps: the local director, the offices in Virginia, or a shift manager.

I've heard and experienced hand swabs (pointless but quick and non-invasive.) I have never heard of direct-to-frisking with no full-body imaging first.

In the era before PreCheck and before full-body imaging, they used to have all of the random upper body/lower body/limited friskings. Those largely went away, except for the side friskings because the "Advanced Imaging Technology" isn't advanced enough to see one side of the body.

After Sharm Al Sheikh, I would imagine that the TSA would put its biggest show of force into perimeter access and employee screening. But that's too difficult, so they're making passengers' lives more difficult.

The 50/50 chance of avoiding ineffective full body imaging (and inevitable post-imaging frisking) still makes PreCheck worthwhile. But it is still laughable.

But the numbers don't lie: the TSA has caught thousands, maybe hundreds of thousands of terrorists, and stopped countless attacks through their bravery, insight, and clever logistics (I'm kidding.)

I'm middle eastern looking and I've almost never had a secondary screening request while having the TSA pre-check logo on my boarding passes.

However, after returning from trips to the middle east and south asia, I've had the dreaded quad-X ("XXXX") printed on my boarding pass, after I was unable to check in online. This is straight secondary screening, to a very high degree (pulling apart each underwear in my carry-on to see if anything is hidden in the crotch, lol).

A few weeks after returning from those overseas trips, no issues.

Another time I've been getting secondary screening consistently is when using my Nexus card when returning to the US, but that's off topic.

What is the official policy/procedure when the WTMD produces a random alarm for an airport employee?

Going through LAX PreCheck today, wheelchair assistance employee set off random alarm. TSO had them exit then re-pass through WTMD normally. I was next and he told me I was randomly selected even though there was no alarm when I went through.

I opted-out for spite

Several years back I had a similar experience following a group of pilots/FA's through the WTMD. No beeps for me but straight to the penalty box when I walked through.

So if you don't wan't to be selected, you should avoid being directly behind an airline or airport employee?

That is the official policy. If someone "special" gets the quota alarm, it's ignored for them and the next non-special traveler gets the quota extra screening.

Excellent :)

I have arms that don't go up fully due to injuries and hardware. I got the random beep. It took three TSA supervisors running around like chicken to allow me to be wanded/pat down. They insisted that when you get the random beep that you have to go through the ATI. This despite me showing them a medical card even to prove the hardware. It took the airport TSA director to knock some sense into them.

HM. So what happens if you are "forced" and cant hold your arms up at all. ?

You get tagged as uncooperative, which means you will get even more screening (bag dump, full pat-down, etc.).

Which is nonsense. The same rationale for randomly screening PreCheck pax further certainly extends to crew or other special people.

In every other country it does. Here in the US we act like airport workers would never do any wrong.