This is a story related achievement and cannot be missed.
After doctor Rosenthal has been killed go the way back you came from. If you are next to the river a boat will wait for you. Jump in and drive as far as possible. Once on land again you won´t have to play very long on and VTOL will fly above your head. Clear out the landing zone which will be attacked by nanosuit soldiers (be aware that they sometimes make themselves invisible so check your radar). Once finished you can jump inside the vehicle and you will get your achievement.