Anecdotally, I had a standby ticket recently when my seat was reassigned to a paying customer, although I still had a boarding pass for that seat. I was halfway down the jet bridge before the gate agent realized that my ticket had been revoked.
I imagine it's second nature for gate agents to let passengers through, and one lapse in judgement can cause the United incident, despite the software showing that the ticket was invalid.
The printout correctly showed that the card contained 100 CNY. I've thought of IKEA ever since as a store where the cash registers are smarter than the cashiers.
On the other hand, when I asked the recipient (it was a wedding gift) about it later, he reported that his wife had recorded it as having an appropriate-given-the-exchange-rate quantity of USD, so I suspect it was in fact usable.
The boarding software usually checks that:
- The boarding pass is valid (checksum)
- The flight state is correct e.g. 'boarding' and 'open'
- The passenger did check-in
- The passenger haven't boarded yet
The beep usually is a response from the reader indicating that the code has been read successfully.
The result of the operation is displayed in a screen and the attendant has to read it and act accordingly.
In Japanese domestic terminals, the gates are definitely more advanced - they play a different chime depending on your frequent flier status.
It's entirely possible that the "check" is "is this boarding pass checksum valid.", especially given the stories of boarding wrong flights - it doesn't even flash red for "this is not the right pass for this flight".
Anecdotally, last time I was flying on a business to Germany with Lufthansa, my cow-orker did the Internet check-in for me without me knowing, and printed out the boarding passes. I later did the check-in for myself again, and picked a different seat. At the airport, the friend gave me the boarding pass he printed (with the old seat number), and so I thought, let's check if it still works on the scanners. I scanned it when boarding, and the scanner threw up an error that the seat on the pass does not agree with the one that's actually booked. I pulled the up-to-date boardin pass on my phone and continued on my way - but it seems that there is some actual checking being done, not just CRC.
Makes me wonder if those are curable in humans, or are we doomed to forever not having nice things because of people acting this way?
So that's a airline specific design decision. It could be that for United, the beep indicates a valid boarding pass of any type, but a display shows the flight info...and the matching is manual.
There is also likely a human error component. When you make someone manually scan 150 people they stop paying attention. They should have some kind of error message, but if it looks like other error messages (like the ask about emergency exit message), it's possible the human confused the error and cleared it.
The shared gate agent computers are built from an industry-standard OS image (8 years or so ago this was Windows XP SP2, and not SP3, never SP3).
Don't just beep the same way every scan beeps, make a different noise. Show a large red "STOP" sign on the screen along with the problem.
When you need to alert a human to an event that only happens once in every few hundred cases, you can't be subtle.
Bingo. This is not really a job that people, in general, are any good at. If there was an automated turnstile that didn't suck, that'd be a great place for one, so they could focus on the exceptional cases instead of being lulled to sleep by the happy path.
I believe that the reader just shows your name.
I also think what the readers do is update the system to say that you are on that flight. This is for revenue reasons. Tickets can be issued by other airlines, and the revenue is not counted until you are on the flight.
Also in Europe the system matches you with your luggage. This is a security measure.
One woman was stopped as she entered the aircraft, as the attendent checking tickets saw that the flight on her ticket was for the day before!
From the numerous comments here, it's not matching the boarding pass to the flight or gate. Is it just boarding group? Is it that "yes, this is a valid ticket" or something else entirely?
Seems like an easy way to "disappear" - basically book a fight going somewhere, look around until you find a flight with open seats (Southwest would be best as no assigned seating), and then... poof?
That's the question that's been nagging me since the day I read about this particular mistake. I wonder if there are any active public subreddits of airline workers; somewhere where I could hear a first-hand account of what those scanners are checking.
This was with Delta (both my intended flight and the mistaken one.)
AFAIK, the scanner only checks "okay this is the airport you supposed to be inside within 48hours timeframe". That's all.