For UK/USA bound flights, are details entered during online check-in, such as date of birth or passport number ever checked by airlines/immigration?

When checking-in for a flight online, you are usually asked for details such as date of birth, passport number, passport expiration dates, etc. However despite making minor mistakes a few times (usually in the expiration date field), I was never once questioned by the airline. I also don't remember them checking anything except my name or my visa status.

So the questions are:

Is passenger information (as entered during online check-in) other than name and visa ever validated by airlines?
Is that information ever validated by immigration?
Will you be denied boarding because you've made a mistake during online check-in?

The question is restricted to UK and USA flights because both are generally strict about requiring APIS data for all inbound flights.

Best Answer

To clarity, validate is a very strong word with different meanings.

Also, these answer are limited exclusively to the information enter in the airline's website at check-in or booking, not at the airport or by an Agent unless otherwise noted.

NO. The carrier has no means to validate any information you enter on line. They take you at you word at this stage. They may compare what you enter for a particular itinerary with your existing profile and flag any differences, but some variations are allowed, such as middle initial vs full middle name. But, the airline gets it validated because of #2.
YES. For flights to/from and within the US and UK, the airline does transmit what you enter online to the appropriate government agency (CBP, TSA, Home Office) ahead of time, sometimes days ahead of time (3 for CBP). YES, the agencies validate the information such as having a valid ESTA for the Passport. This is done to flag any errors or...mistakes...as far ahead of time as possible. If you make a mistake during booking and don't notice it at online check-in, you may not be able to complete online check-in.
UNLIKELY BUT POSSIBLE. In most cases, it will depend on how much time there is to correct any mistakes and this doesn't happen often because the vetting process begins well ahead of the flight. Important note: You can be denied boarding because the information is incorrect and cannot be corrected, not merely because you entered it wrong on the website.

For instance, if you mistype the passport number, entering one that matches to someone else or does not match a current ESTA, they may/should reject that forcing you to complete check-in at the airport by scanning your Passport. At this point, the scanned data overrides what you messed up online and the the carrier resends the APIS message. That alone will clear up most issues.

Sources:
APIS: Advance Passenger Information System - The airline must report accurately so they have 'check' on their own first.

CBP/TSA Consolidated User Guide - Probably a newer version, but this one's directly linkable.

International travel document requirements - Specifies denied boarding and UA was the subject of the other thread.

Passports, visas and API

What do US customs see when they swipe passports?

“Do not board” message at the airport check-in? - Both the airline and CPB had to 'check' the passengers data for this to happen.

Pictures about "For UK/USA bound flights, are details entered during online check-in, such as date of birth or passport number ever checked by airlines/immigration?"

Do I need to enter passport details before I fly?

Most airlines and third-party travel sites don't require you to input a passport number at the time of booking. At that point, the only information you'll need is contact, payment and billing information.

Do airlines share information with immigration?

Additionally, airlines send passenger manifest information to U.S. Customs and Border Protection (CBP) in advance of boarding. That way, CBP can alert the airline if particular passengers should be turned away and not permitted to board.

Does airline check passport?

They will check your passport. When you check in for the flight, the airline will need to document your identity (via your passport) and also if you have the proper visas or permissions to enter the country, as the airline will be fined if they knowingly board you without proper documents.

Does your airline ticket have to match your passport UK?

Even though your boarding pass may not match your government-issued ID (i.e. your middle name is not on it), if your passenger information is correct, there will not be a problem. Bottom Line: Even if you forget to put your middle name in when booking your ticket, chances are there will be no issues when flying.

How forged passports are caught in UAE

Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.

Images: Torsten Dettlaff, Vlada Karpovich, Vlada Karpovich, Vlada Karpovich