Do I need to fly with passport when API is required?

Question

I am an EU citizen planning to fly from Switzerland to England (London). I usually use the app from my airline to do online check-in and then just walk up to security. In this case, though, the airline is requiring my passport information to complete the online check-in. This never happened to me before.

Looking online, it seems that I need to provide my passport information as part of the API (Advanced Passenger Information) required to travel to the UK and other countries. I can do so, but I would rather bring my national ID than my passport on my travel (I am allowed to do so, being an EU citizen). I am wondering if this is allowed.

So my questions are:

1. The API regulation was introduced in 2006. Why is this the first time that my airline has required me for the passport information before doing the online check-in?
2. If I input my passport information for the API, can I travel there with my national ID and leave my passport at home?

Answer 1

Wherever it asks for your "passport number", just put in your ID card number instead.

"Passport number" is a generic term, which really means "travel document number". So don't take it too literally.

So no need to complicate this: again, just put your ID card number in the API system.

Answer 2

As outlined in a related question, airlines never bother checking the details you've entered during online check-in. They're essentially junk as they'll be written over anyway when they scan your passport or ID card at the gate. So feel free to enter whatever you want into the field, just make sure to keep your citizenship correct so that you're not asked to check-in at the gate (usually an issue with low cost airlines).

And yes, you may certainly travel with an ID card anywhere within the EU. Lots of travelers from countries which issue ID cards don't even have a passport so restricting passengers to using passports would be quite harmful to the airlines revenue.