There remains a locked flyer mission in my "play mini-games" menu.

There are 14 entries but the last one is locked:

Returning Home
Leaving the Town
Leaving the Workshop
Kang's First Mission
Kang's Second Mission
Spirit Journey
A Test for Hin Goo
Escort the Prefect
Rescue Mission
The Battle of Dirge
Encounter in the Skies #1
Encounter in the Skies #2
Encounter in the Skies #3
( locked )

Does anyone know how to access this last mission ? I finished the game (more than once, even on JM) and this still doesn't show up. I try to always "attack" when there is a flyer transition.