Can I enter Turkey on one passport and leave for a month on different one

lambshaanxy explains why "You have to use the same passport to enter and exit" a country. But to exit going to C, if that passport needs a visa for C and you don't have one, you can't board the plane. Once you arrive in C, you could show the other passport, but if you already have a visa, why?

If Turkey AND the other country don't require a visa for passport A, then why not just use A for both?

When entering a country as a tourist what you want to be is ordinary. Boring. Do not make a special case. Everywhere in the world border officials have extremely broad decision powers. If they do not like what they see they can refuse and pursuing a legal challenge very rarely will lead to anything good. What I mean here is even when we can not point to a specific written regulation it does not mean you will not be refused.

That said, let's look at the stays and their patterns -- still not talking about Turkey or visas: you want to enter for three days then want to enter the same country for six days more than a month later. Again a very primary rule for border officials is they want to make sure the person seeking to enter has a credible story of leaving on time and not becoming an illegal worker in the country. What you described does not, by any means, paint a picture where someone is planning to reside. As an example, if you entered for three months, stayed out for two days and then came back for another three month stay, that would be a very different picture and most places would refuse.

With all that said, don't do any complicated dance. Use one of your passports to enter and use the same to leave. You will be just fine. Since you already planned to enter with your visa free passport just use it both times and be done.

It’s important you remember that the passport you show the airline does not need to be the passport you show to exit passport control.

You should show the airline (when filling in API information online, during check-in, at the gate) the passport you intend to use when entering the destination country. What they are interested in is:

• that you are who you say you are - either passport would do
• That you are allowed to enter the destination country, based on citizenship, any visas or resident permits, or ETA/ESTA-like systems.

This is the information they will be submitted via API/APIS-like systems to the destination country, and which may result in Board/Do not board decisions for systems which implement it.

On the other hand, you should show exit passport control the passport which is relevant to exit the country you are leaving, most likely the one you used to enter, as this will allow them to match records and/or input stamps, and allow them to decide whether you were legally present in the country, did not overstay, etc.

If you show them a different passport, depending on the combination of countries (the one you are exiting, the one for the passport you present…) this could raise eyebrows as in “can’t find the entry stamp” or “can’t find your record”, etc.

There are a few peculiar cases, such as countries which do not have explicit exit controls (like the US or UK) where whatever you give the airline will also be sent to the authorities of the country you are leaving. They apparently have some way of matching your record for that case (but if you’re a foreigner in that country, it’s good to check that your records are properly updated, like your I-94 in the US).

You have to use the same passport to enter and exit each country. If you enter on passport A and try to leave on passport B, the immigration computer will go "ding" because there is no record of B entering Turkey, and you will need to explain to grumpy people where B came from and what you're trying to do etc etc.

The good news is, you can simply leave Turkey with passport A, use either passport A or B in your next destination, and then re-enter Turkey with passport B.

See also: I have two passports/nationalities. How do I use them when I travel?