Landfall (achievement)
From Halopedia, the Halo wiki
Landfall
Landfall is an Achievement for Halo 3 on the Xbox 360.
It is earned when one finishes the campaign mission Sierra 117 on the Normal, Heroic, or Legendary difficulties. This achievement is worth 20 Gamerpoints.
Note: you must finish the level compleatly threw without quiting or it wont count.
References