How do you respawn and skydive onto a team deathmatch multiplayer map in battlefield 3?

Ive seen a lot of people free falling in team deathmatch and parachuting onto the map after they die but I thought the only way to free fall onto a multiplayer map was to bail out of a chopper or jet and I thought those vehicles are only on rush or conquest. How are they doing this???How do you respawn and skydive onto a team deathmatch multiplayer map in battlefield 3?
If someone on your team chooses the recon class and uses the mobile spawn point equipment. You can choose to spawn in the air and drop down. So if you have a super sneaky recon guy he can plant it in the enemies base and you can either spawn on the ground or the air.