I have 2 passports. Both passports are of the same citizenship, UK. In passport 1 have a visa for, let's say, 'country A'. In passport 2 I have a visa for 'country B'. I am living in country 'A' and want to travel to country 'B' (neither is UK). There are direct flights, it is not an issue to travel between these countries.
To leave country 'A' I must book the flight using passport 1 (same passport as I entered on and has the entry stamp / requires the exit stamp from country 'A').
When arriving in country 'B' I need to use passport 'B' as it has the correct visa. Will they question why my incoming flight booking was made using a different passport?
Thanks everyone for the answers.
Countries A and B are India and China. It appears China will be opening up again soon / reducing restrictions on flights. I just realised it actually becomes more complicated if I book a return ticket.
From my experience for flights to India and China I have always been required to submit passport details during booking flight tickets. And as I mentioned earlier when leaving a country (with visa / entry stamps in your passport) you must use the same passport as you entered with, otherwise their system will not link the different passport numbers and you could face an issue when returning (because it would look like you never left).