Suspended Pelican

It is possible to see a Pelican dropship suspended in mid-air on the level, Metropolis.

Directions
Play through the level Metropolis until two Pelican dropships arrive, this is right before you meet Corporal Perez. The Pelican with the attached Scorpion Tank will fly above the building and freeze in place. If you shoot rockets or Wraith mortars at the pelican (with the Sputnik skull) until it moves about 50(?) ft. and then go up the staircases, the marines (and the sergeant) and the tank won't be there. The Scarab will still briefly pause, but it won't shoot at where the tank used to be.