Most of us at one point or another have used miles to fly on partner airlines within the same alliance. One of my favorite redemptions include using my British Airways Avios for American Airlines flights (because they follow a distance-based award chart, often making it “cheaper” in miles to fly domestically).
When you book with miles of a particular airline, your reservation generates a 6-character record locator that is specific to that airline itself. The partner airline that you’re ticketed on has its own unique record locator that is tied to your ticket that could be used to access your reservation on the airline you’re flying to change seats, have your ticket recognize your elite status etc.
Up until recently, I found it easy to just tweet the airline that I was flying, asking if they could provide me the airline-specific record locator using my ticket number. In my experience, I would receive a response back in minutes.
I must have been living under a rock because my friend Jamison pointed me to an easier way: checkmytrip.com (for reservations from airlines using the Amadues reservation system).
With Check My Trip, all you have to do is simply input your record locator, and it will display the partner record locator (in my example below, the record locator on the top right is my British Airways one, the associated American Airlines one is all the way at the bottom).