New Ways to Save a QuidG 10

In the New Alexandria level you have a chance to get a side objective where you escort Sgt. Buck's Falcon across the map. If RNG is on your side, Buck will radio asking for assistance and the achievement will unlock.

You can increase your odds of encountering Buck by playing co-op with 3 or 4 players (according to the Halopedia)

https://www.halopedia.org/New_Ways_to_Save_a_Quid