Why are passports checked at the check-in counter, Immigration and even at the gate?

The details vary but the thing is that the states themselves made it a “third-party company”'s responsibility to check passengers' immigration status. If a carrier brings someone without documentation and this person is denied entry, they will have to bring him or her back and can face a fine. Furthermore, for US-bound planes, airlines are also required to collect “advance passenger information” and communicate them to the US authorities.

In both cases, it's the destination state that imposes these requirements so immigration officers from the departure state don't care much. The goal of all this is to have some way to filter passengers before they even set foot in the country (either because they might be trying to immigrate illegally or apply for asylum or because they are on a no-fly list or are deemed to present some security risk). In a few places (Ireland, Canada…), the US has immigration officers posted abroad to (pre)clear people even before boarding the plane but most of the time, it has to rely on private companies to do its bidding everywhere in the world.

Finally, (some) airlines also want to check ID for their own purposes, mostly to enforce their price discrimination tactics but in this case you just need a quick match between the name, the document and the person, no need to check visas or enter any detail in a computer.

Why they would again check immigration status at the gate (as opposed to simply matching your name and the name on your boarding card), I don't know but it might be because some people use automated check-in and did not encounter any agent of the airline yet. In any case, you need to check ID again at that point otherwise any previous check could be circumvented (e.g. book a ticket under another person's name, let that person show up at check-in with her genuine ID and then proceed to the gate using only the boarding pass).

There can be a couple of reasons for this -- one they could all be working for different people or trying to catch different things.

At check-in the airline needs to know that you'll be allowed to get into your destination (and the UK & US are somewhat stricter than a lot of places). At border control the officer needs to know that you're allowed to leave and that you were there legally, generally they're less concerned about where your going but they to might want to make sure you're not going to get bounced back. At the gate there may be checks in order to catch passengers transiting from a different airport/airline who may have missed the other checks.

Alternatively the gate check people could be working for UK/US immigration doing pre-checks.

Alternatively they could all be working for the same people but they're redoing the checks to make sure you haven't swapped passports or just to be careful to ensure that nothing is missed.

In most airports it's not so bad -- the gate passport check, if they do one, is just to confirm ID. In some places you'll get a sticker to say you've been cleared and it makes later checks faster.

And there are so many complex rules that if you have an uncommon passport or visa they often have to check. I have an odd visa and I've had check-in staff pull out a huge paper book of example visas and flick through it to try and confirm mine is correct.

All these people are just doing their job, there are consequences for them if they make a mistake. If they're unsure about anything it's in their interests to double check.

Could it be done faster? Probably, but that would probably cost more money than it's worth in the long run.

The reasons for checking your passport vary. The checkin staff are doing two things: confirming you are indeed the person named on your ticket, and confirming (with the help of their computerized system) that you will be allowed to make your journey. They do this because if you are not allowed into your destination country, or to make a transit, their airline will have to pay to return you to your starting point or your home country. They are trying to avoid that expense by checking your status.

Just before security, in many US airports, your passport is again checked to make sure you personally (as in the person who matches the picture) are allowed into the secure area that is for passengers only. You can of course forge a web checkin style boarding pass easily enough, so they also sometimes scan your boarding pass to check with some other system that someone with your name really is on that flight today. This check doesn't care about your immigration status, just that you really are a passenger. They may ask you some questions, just to see how you react. If so, they choose questions people expect to be asked in airports like "Where are you headed today?" As well, in many airports they are making sure you're in the right terminal or line - I once lined up for domestic security and had to be told to head over to a different line for international security. That's not checking your visa, even if the questions seem similar.

In many European airports there is an exit immigration check. Here they are not so much checking as they are recording. They swipe your passport not so they can look you up in the system, but to tell the system you have left. You may find it difficult to leave the airport should you change your mind about flying after you've been marked as having left.

At the gate, some people have not yet been checked by the airline to ensure they are able to fly. These people typically check in online and don't check luggage, so they can just head for the gate without interacting with airline staff. The security and exit checks were not to serve any purpose of the airline (saving them the cost of bringing you back) and do not pass information about you back to the airline. The gate staff page these people, look at their passports, and do something involving their computer system that is the same as what would have happened if the people had already interacted with airline staff.

As you actually board, the airline staff again look at your passport and your picture, this time ensuring that the person they are letting onto the plane is the person who bought the ticket and whose immigration status has been so carefully checked. Imagine you are allowed into country A but not B, and you want to go to B. You could buy a ticket to A, and get a friend to buy a ticket to B, both check in and get boarding passes, and at the last minute you use your friend's boarding pass to go to B while your friend either goes to A or cancels at the last minute. That would cost the airline to send you back when you weren't allowed into B, so they check again one more time.

It doesn't stop there. Sometimes there is a passport check on the jetway as you leave the plane. I am not really clear why but I think it is to ensure people from different flights don't meet and exchange documents. Imagine again you are not allowed into B but have somehow managed to get there. If a friend who is allowed into B can land there at the same time as you and pass you a passport, you can get into B using it and the friend can either be deported (maybe they don't mind) or can say they lost their passport and get let in using some other ID. (This seems kind of pointless when the friend could mail you the passport in advance and you could use one to board and one to land, but I don't know why else they do these jetway checks.)

It's frustrating, because you think your passport is conveying the same information every time. But it's not. It's always confirming who you are, and most of the time it is not being used to confirm you're allowed to enter the country you're going to.

Security. Process. Security. Sanity.

At least, those are the words I mumble to myself as I progress through these repeated checks ;)

Some reasons and logic:

1. They need to check at the check-in gate to ensure that their carrier is allowed to take you. As such, they need to ensure that you have a valid passport, with a valid visa (and usually a return ticket as well)
2. At immigration (if they have it) they need to check if you overstayed, record your departure, and stamp you out (potentially).
3. At the gate, they're double checking that you're you, matching it to your ticket, and again, ensuring that your passport is valid etc.

At any number of other points (extra screening, x-ray machine, help desk) there may be an additional check, for record keeping, to match you to your bag (your baggage claim number is often stuck to the back of your passport these days).

So while a lot of it may seem redundant, each department has their own reasons and need to check. And yes it can be slow, dull and all that, but once you're on that plane - you're on your way!

(Until they check on your flight as well)

At the jet way upon arrival, passport checks are only conducted because of the following:

1. the destination authorities have a heads up information of a person of interest or an unwanted immigrant.

2. Most of the time such checks are done if the aircraft arrives from a country which is well known as a transit point for illegal immigrants.

3. Some rogue airline employees collaborate with human human traffickers and are well known for ferrying passengers using falsified documents.

4. Some asylum seekers flush their documents in the aircraft lavatories and arrive undocumented. So it's easy for the authorities to determine where they arrived from and are most of the time returned back into the same aircraft back to their origin destination.

Its quite simple - it is the only way to identify you that is universally accepted.

At the check-in, they need to make sure you (the person standing in front) match your name (which is printed on your passport) and that it further matches the name on the reservation.

If you are flying internationally, they will further check the passport to make sure you have the correct documentation for your destination.

If required - at immigration, your passport is the document that is verified to ensure that you are eligible to exit the country - in most cases it also serves as proof of legal exit (via the stamps) - although some countries are now employing electronic visa schemes that are "stamp free"; although you still need your passport.

At the gate - they need to check if you are the correct person; in case someone has stolen your boarding pass - as it does happen.

So I can see the justification behind this - although its one of those things that have become so routine that I just go with the flow.

Here is what really tickles my noodle though - that despite the counter printing your boarding pass, the check in gate scanning your boarding pass - the flight stewards at the door still ask to see your boarding pass.

As if at that point you would have boarded the wrong plane - although I imagine sometime ago it must have happened and now its just another one of those things.

This is specific to Istanbul (or maybe Ankara to). They want to make sure you don't have an obvious problem to enter UK or US for the cost of crossing their boundaries, kind of over helping but actually saves some people.